0001654151-20-000003 | 10-K | XBRL Viewer | Deciphera Pharmaceuticals INC

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2019	Feb. 28, 2020	Jun. 28, 2019
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Trading Symbol	DCPH
Entity Registrant Name	DECIPHERA PHARMACEUTICALS, INC.
Entity Central Index Key	0001654151
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Shell Company	false
Smaller Reporting Company	true
Emerging Growth Company	true
Entity Ex Transition Period	true
Document Transition Report	false
Entity Address, State or Province	MA
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		55,645,277
Entity Public Float			$ 445.5

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 120,320	$ 293,764
Marketable securities	459,256	0
Prepaid expenses and other current assets	13,832	7,273
Total current assets	593,408	301,037
Long-term investment—restricted	1,510	1,069
Property and equipment, net	6,333	13,453
Operating lease assets	21,158	0
Total assets	622,409	315,559
Current liabilities:
Accounts payable	19,575	8,308
Accrued expenses and other current liabilities	38,716	13,709
Operating lease liabilities	1,747	539
Notes payable to related party	0	187
Total current liabilities	60,038	22,743
Notes payable to related party, net of current portion	0	1,107
Operating lease liabilities, net of current portion	15,904	11,347
Other long-term liabilities	0	381
Total liabilities	75,942	35,578
Commitments and contingencies (Note 15)
Stockholders' equity:
Preferred stock, $0.01 par value per share; 5,000,000 shares authorized; no shares issued or outstanding	0	0
Common stock, $0.01 par value per share; 125,000,000 shares authorized; 51,617,639 shares and 37,676,760 shares issued and outstanding as of December 31, 2019 and 2018, respectively	516	377
Additional paid-in capital	1,033,819	575,327
Accumulated other comprehensive income (loss)	111	0
Accumulated deficit	(487,979)	(295,723)
Total stockholders' equity	546,467	279,981
Total liabilities and stockholders' equity	$ 622,409	$ 315,559

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	125,000,000	125,000,000
Common stock, shares issued (in shares)	51,617,639	37,676,760
Common stock, shares outstanding (in shares)	51,617,639	37,676,760

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenues	$ 25,000	$ 0	$ 0
Operating expenses:
Research and development	157,610	82,887	39,514
Selling, general, and administrative	68,116	21,212	11,421
Total operating expenses	225,726	104,099	50,935
Loss from operations	(200,726)	(104,099)	(50,935)
Other income (expense):
Interest and other income, net	8,537	4,329	746
Interest expense	(67)	(84)	(95)
Total other income (expense), net	8,470	4,245	651
Net loss	$ (192,256)	$ (99,854)	$ (50,284)
Weighted average common shares outstanding—basic and diluted (in dollars per share)	$ (4.48)	$ (2.82)	$ (2.99)
Weighted average common shares outstanding—basic and diluted (in shares)	42,869,058	35,390,480	16,792,179
Comprehensive loss:
Net loss	$ (192,256)	$ (99,854)	$ (50,284)
Other comprehensive income (loss):
Unrealized gains (losses) on marketable securities	111	0	0
Total other comprehensive income (loss)	111	0	0
Total comprehensive loss	$ (192,145)	$ (99,854)	$ (50,284)

CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED SHARES AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Shares	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Series A, B-1, B-2 and C Convertible Preferred Shares
Convertible preferred shares, beginning balance (in shares) at Dec. 31, 2016						3,632,711
Convertible preferred shares, beginning balance at Dec. 31, 2016						$ 192,667
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of Series C convertible preferred shares, net of issuance costs (in shares)						690,333
Issuance of Series C convertible preferred shares, net of issuance costs of $429	$ 0					$ 51,871
Effect of Conversion (Note 1), convertible preferred shares (in shares)						(4,323,044)
Effect of Conversion (Note 1), convertible preferred shares						$ (244,538)
Convertible preferred shares, ending balance (in shares) at Dec. 31, 2017						0
Convertible preferred shares, ending balance at Dec. 31, 2017						$ 0
Beginning balance (in shares) at Dec. 31, 2016		0
Beginning balance at Dec. 31, 2016	(139,760)	$ 0	$ 5,825	$ 0	$ (145,585)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of Conversion (Note 1) (in shares)		24,425,190
Effect of Conversion (Note 1)	244,538	$ 244	244,294
Issuance of common stock sold in public offering, net of underwriting discounts, commissions and offering costs (in shares)		8,166,496
Issuance of common stock sold in public offering, net of underwriting discounts, commissions, and offering costs	$ 124,613	$ 82	124,531
Issuance of common stock upon exercise of stock options (in shares)	0
Stock-based compensation expense	$ 4,866		4,866
Net loss	(50,284)				(50,284)
Ending balance (in shares) at Dec. 31, 2017		32,591,686
Ending balance at Dec. 31, 2017	183,973	$ 326	379,516	0	(195,869)
Convertible preferred shares, ending balance (in shares) at Dec. 31, 2018						0
Convertible preferred shares, ending balance at Dec. 31, 2018						$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock sold in public offering, net of underwriting discounts, commissions and offering costs (in shares)		4,945,000
Issuance of common stock sold in public offering, net of underwriting discounts, commissions, and offering costs	185,259	$ 50	185,209
Issuance of common stock upon exercise of stock options (in shares)		140,074
Issuance of common stock upon exercise of stock options	915	$ 1	914
Stock-based compensation expense	9,688		9,688
Net loss	(99,854)				(99,854)
Ending balance (in shares) at Dec. 31, 2018		37,676,760
Ending balance at Dec. 31, 2018	279,981	$ 377	575,327	0	(295,723)
Convertible preferred shares, ending balance (in shares) at Dec. 31, 2019						0
Convertible preferred shares, ending balance at Dec. 31, 2019						$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock sold in public offering, net of underwriting discounts, commissions and offering costs (in shares)		12,432,431
Issuance of common stock sold in public offering, net of underwriting discounts, commissions, and offering costs	$ 431,780	$ 124	431,656
Issuance of common stock upon exercise of stock options (in shares)	1,504,583	1,508,448
Issuance of common stock upon exercise of stock options	$ 6,441	$ 15	6,426
Stock-based compensation expense	20,410		20,410
Unrealized gains (losses) on marketable securities	111			111
Net loss	(192,256)				(192,256)
Ending balance (in shares) at Dec. 31, 2019		51,617,639
Ending balance at Dec. 31, 2019	$ 546,467	$ 516	$ 1,033,819	$ 111	$ (487,979)

CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED SHARES AND STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Series C Convertible Preferred Shares
Issuance costs	$ 429

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (192,256)	$ (99,854)	$ (50,284)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	20,410	9,688	4,866
Depreciation expense	830	317	150
Loss on disposal of property and equipment	0	0	10
Net accretion of discounts on marketable securities	(3,999)	0	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(10,321)	(5,770)	(637)
Operating lease assets	958
Accounts payable	10,862	3,991	2,904
Accrued expenses and other current liabilities	24,189	4,477	6,276
Operating lease liabilities	(319)
Other long-term liabilities	350	368	13
Net cash flows used in operating activities	(149,296)	(86,783)	(36,702)
Cash flows from investing activities:
Purchases of marketable securities	(817,142)	0	0
Maturities of marketable securities	261,216	0	0
Sales of marketable securities	100,780	0	0
Purchases of property and equipment	(4,935)	(1,125)	(406)
Increase in restricted investments	(441)	(1,069)	0
Net cash flows used in investing activities	(460,522)	(2,194)	(406)
Cash flows from financing activities:
Proceeds from public offerings, net of underwriting discounts and commissions	432,400	185,933	129,112
Proceeds from issuance of convertible preferred shares	0	0	52,300
Repayment of notes payable to related party	(1,294)	(187)	(187)
Payments of public offering costs	(620)	(674)	(4,395)
Payments of convertible preferred share issuance costs	0	0	(429)
Proceeds from exercise of stock options	5,888	915	0
Net cash flows provided by financing activities	436,374	185,987	176,401
Net increase (decrease) in cash and cash equivalents	(173,444)	97,010	139,293
Cash and cash equivalents at beginning of period	293,764	196,754	57,461
Cash and cash equivalents at end of period	120,320	293,764	196,754
Supplemental disclosure of cash flow information:
Cash paid for interest	67	84	95
Addition of operating lease asset included in accrued expenses and other current liabilities	562	0	0
Supplemental disclosure of non-cash investing and financing activities:
Amounts capitalized under build-to-suit lease transaction	0	11,885	0
Purchases of property and equipment included in accounts payable and accrued expenses and other current liabilities	661	0	78
Retirement of assets	217	0	0
Conversion of convertible preferred shares into common stock	0	0	244,538
Unsettled exercise of stock options	$ 553	$ 0	$ 0

Nature of the Business and Basis of Presentation	12 Months Ended
Nature of the Business and Basis of Presentation	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business and Basis of Presentation	Nature of the Business and Basis of Presentation Deciphera Pharmaceuticals, Inc. (the Company) is a clinical-stage biopharmaceutical company focused on improving the lives of cancer patients by tackling key mechanisms of drug resistance that limit the rate and/or durability of response to existing cancer therapies. The Company's small molecule drug candidates are directed against an important family of enzymes called kinases, known to be directly involved in the growth and spread of many cancers. The Company uses its understanding of kinase biology together with a proprietary chemistry library to purposefully design compounds that maintain kinases in a "switched off" or inactivated conformation. These investigational therapies comprise tumor-targeted agents designed to address therapeutic resistance causing mutations and immuno-targeted agents designed to control the activation of immunokinases that suppress critical immune system regulators, such as macrophages. The Company has used its platform to develop a pipeline of tumor-targeted and immuno-targeted drug candidates designed to improve outcomes for patients with cancer by improving the quality, rate, and/or durability of their responses to treatment that includes three clinical-stage, one preclinical-stage, and one research-stage program. The Company wholly owns all of its drug candidates with the exception of a development and commercialization out-license agreement for the Company's lead drug candidate, ripretinib, in Mainland China, Hong Kong, Macau, and Taiwan, each a Region and collectively the Territory, also referred to as Greater China or the Greater China region. The Company is subject to risks and uncertainties common to companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, ability to complete late-stage clinical trials, ability to obtain and maintain regulatory approvals, ability to prepare for and successfully launch drug candidates that are approved for marketing, compliance with government regulations, and the ability to secure additional capital to fund operations. Drug candidates currently under development will require significant additional research and development efforts, including extensive preclinical and/or clinical testing and regulatory approval, as well as continuing to build a commercial infrastructure, prior to commercialization for the Company's drug candidates, including ripretinib, if approved. These efforts require significant amounts of additional capital, adequate personnel and infrastructure, and extensive compliance-reporting capabilities. Even if the Company's drug development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. On October 2, 2017, immediately prior to the completion of its initial public offering (IPO), the Company engaged in a series of transactions whereby Deciphera Pharmaceuticals, LLC became a wholly owned subsidiary of Deciphera Pharmaceuticals, Inc., a Delaware corporation. As part of the transactions, shareholders of Deciphera Pharmaceuticals, LLC exchanged their shares of Deciphera Pharmaceuticals, LLC for shares of Deciphera Pharmaceuticals, Inc. on a one-for-5.65 basis (the Conversion). In October 2017, Deciphera Pharmaceuticals, Inc., completed the IPO, pursuant to which it issued and sold 8,166,496 shares of common stock at the IPO price of $17.00 per share, resulting in net proceeds of $124.6 million after deducting underwriting discounts and commissions and other offering expenses. Upon the closing of the IPO, the Company's outstanding convertible preferred shares automatically converted into shares of common stock. In June 2018, the Company issued and sold 4,945,000 shares of its common stock in a follow-on public offering at a public offering price of $40.00 per share, resulting in net proceeds of $185.3 million after deducting underwriting discounts and commissions and other offering expenses. In the third quarter of 2019, the Company issued and sold 12,432,431 shares of its common stock in a follow-on public offering at a public offering price of $37.00 per share, resulting in net proceeds of $431.8 million after deducting underwriting discounts and commissions and other offering expenses. In February 2020, the Company issued and sold 3,659,090 shares of its common stock in a follow-on public offering at a public offering price of $55.00 per share, resulting in net proceeds of $188.4 million after deducting underwriting discounts and commissions and other offering expenses. The accompanying consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities, and commitments in the ordinary course of business. Since inception, the Company has incurred recurring losses including net losses of $192.3 million, $99.9 million, and $50.3 million for the years ended December 31, 2019, 2018, and 2017, respectively. As of December 31, 2019, the Company had an accumulated deficit of $488.0 million. The Company expects to continue to generate operating losses in the foreseeable future. The Company expects that its cash, cash equivalents, and marketable securities of $579.6 million as of December 31, 2019, together with the proceeds from the recent follow-on offering of common stock in February 2020, will be sufficient to fund its operating expenses and capital expenditure requirements through at least 12 months from the issuance date of these consolidated financial statements. The future viability of the Company is dependent on its ability to raise additional capital to fund its operations. The Company expects its expenses to increase substantially in connection with ongoing activities, particularly as the Company advances its clinical trials for its drug candidates in development and engages in efforts to support commercialization should ripretinib receive regulatory approval. Accordingly, the Company will need to obtain substantial additional funding in connection with continuing operations. If the Company is unable to raise capital when needed, or on attractive terms, it could be forced to delay, reduce, or eliminate its research or drug development programs or any future commercialization efforts. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. These consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated. Certain prior year amounts have been reclassified to conform to current year presentation. These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (U.S.) (GAAP).

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, the accrual for research and development expenses, the valuation of common stock prior to the Company's IPO, and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.

Segment Information

The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company's singular focus is improving the lives of cancer patients by tackling key mechanisms of drug resistance that limit the rate and/or durability of response to existing cancer therapies. All of the Company's tangible assets are held in the U.S.

Revenues

The Company accounts for its one license arrangement, entered into in June 2019, under Accounting Standards Codification (ASC) Topic 606, Revenue From Contracts With Customers (ASC 606). For additional information on the Company's license agreement, please read Note 3, License Agreement, to these consolidated financial statements. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price, including variable consideration, if any; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration to which it is entitled in exchange for the goods or services it transfers to the customer.

The Company assesses the goods or services promised within each contract and determines those that are performance obligations. Arrangements that include rights to additional goods or services that are exercisable at a customer's discretion are generally considered options. The Company assesses if these options provide a material right to the customer and if so, they are considered performance obligations. The identification of material rights requires judgments related to the determination of the value of the underlying license relative to the option exercise price, including assumptions about technical feasibility and the probability of developing a candidate that would be subject to the option rights. The exercise of a material right is accounted for as a contract modification for accounting purposes.

The Company assesses whether each promised good or service is distinct for the purpose of identifying the performance obligations in the contract. This assessment involves subjective determinations and requires management to make judgments about the individual promised goods or services and whether such are separable from the other aspects of the contractual relationship. Promised goods and services are considered distinct provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer (that is, the good or service is capable of being distinct) and (ii) the entity's promise to transfer the good or service to the customer is separately identifiable from other promises in the contract (that is, the promise to transfer the good or service is distinct within the context of the contract). In assessing whether a promised good or service is distinct, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. The Company also considers the intended benefit of the contract in assessing whether a promised good or service is separately identifiable from other promises in the contract. If a promised good or service is not distinct, an entity is required to combine that good or service with other promised goods or services until it identifies a bundle of goods or services that is distinct.

The transaction price is then determined and allocated to the identified performance obligations in proportion to their standalone selling prices (SSP) on a relative SSP basis. SSP is determined at contract inception and is not updated to reflect changes between contract inception and when the performance obligations are satisfied. Determining the SSP for performance obligations requires significant judgment. In developing the SSP for a performance obligation, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. The Company validates the SSP for performance obligations by evaluating whether changes in the key assumptions used to determine the SSP will have a significant effect on the allocation of arrangement consideration between multiple performance obligations.

If the consideration promised in a contract includes a variable amount, the Company estimates the amount of consideration to which it will be entitled in exchange for transferring the promised goods or services to a customer. The Company determines the amount of variable consideration by using the expected value method or the most likely amount method. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. At the end of each subsequent reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis in the period of adjustment.

If an arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company's control or the licensee's control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received.

For arrangements with licenses of intellectual property that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes royalty revenue and sales-based milestones at the later of (i) when the related sales occur, or (ii) when the performance obligation to which the royalty has been allocated has been satisfied.

In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less.

The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied, either at a point in time or over time, and if over time, recognition is based on the use of an output or input method.

Cash Equivalents

The Company considers all highly liquid investments with original maturities of 90 days or less at the date of purchase to be cash equivalents.

Marketable Securities

Marketable securities consist of investments with original maturities greater than 90 days at the date of purchase. As of December 31, 2019, Company's marketable securities were comprised of debt securities and the Company considers its marketable securities portfolio to be available-for-sale.

Available-for-sale marketable debt securities are recorded at fair market value and unrealized gains and losses are included in accumulated other comprehensive income (loss) in equity, net of related tax effects. Unless the security has experienced a credit loss, the Company has determined that the Company has the intent to sell the security or the Company has determined that it is more likely than not that the Company will have to sell the security before its expected recovery. Realized gains and losses are reported in other income (expense), net, within the consolidated statements of operations and comprehensive loss on a specific identification basis.

The Company conducts periodic reviews to identify and evaluate each investment in the Company's portfolio that has an unrealized loss, in accordance with the meaning of other-than-temporary impairment and its application to certain investments. An unrealized loss exists when the current fair value of an individual security is less than its amortized cost basis. Unrealized losses on available-for-sale debt securities that are determined to be temporary, and not related to credit loss, are recorded, net of tax, in accumulated other comprehensive income (loss).

When determining whether a decline in value is other than temporary, the Company considers several factors, including whether the Company has the intent to sell the security and whether it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis. No declines in value were deemed to be other than temporary during the year ended December 31, 2019.

Concentrations of Credit Risk and of Significant Suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents, and marketable securities. The Company maintains all cash, cash equivalents, and marketable securities at one accredited financial institution. The Company attempts to minimize the risks related to cash, cash equivalents, and marketable securities by investing in a broad and diverse range of financial instruments as defined by the Company. The Company has established guidelines related to credit ratings and maturities intended to safeguard principal balances and maintain liquidity. The marketable securities portfolio is maintained in accordance with the Company's investment policy, which defines allowable investments, specifies credit quality standards and limits the credit exposure of any single issuer. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.

Long-Term Investment—Restricted

The Company's long-term investment—restricted balance is comprised of certificates of deposit. The certificates of deposit are held to secure letters of credit associated with the Company's lease for space at its headquarters location and to secure a credit card. The balances of such accounts are classified as non-current and are measured at carrying value in the consolidated balance sheets.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset as follows:


Asset Category			Estimated Useful Life
Lab equipment			5 to 7 years
Computer equipment			3 to 5 years
Furniture and fixtures			7 years
Leasehold improvements			Shorter of life of lease or 15 years

Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in the consolidated statements of operations and comprehensive loss. The cost of normal, recurring, or periodic repairs and maintenance activities are expensed as incurred.

Impairment of Long-Lived Assets

Long-lived assets consist of property, equipment, and operating lease assets. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets or asset group may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. The Company did not record any impairment losses on long-lived assets during the years ended December 31, 2019, 2018, or 2017.

Fair Value Measurements

Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

•Level 1—Quoted prices in active markets for identical assets or liabilities.

•Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

•Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies, and similar techniques.

The Company's cash equivalents and marketable securities are carried at fair value, determined according to the fair value hierarchy described above. For additional information on the Company's fair value hierarchy, please read Note 4, Marketable Securities and Fair Value Measurements, to these consolidated financial statements. The carrying values of the Company's accounts payable and accrued expenses approximate their fair values due to the short-term nature of these liabilities. Notes payable to a related party are measured at carrying value in the consolidated balance sheets. The fair value of the Company's outstanding notes payable to related party as of December 31, 2018 approximated $1.1 million. In December 2019, the Company repaid the outstanding balance of its notes payable to related party. The fair value of the outstanding debt was estimated using a discounted cash flow analysis based on current market interest rates for debt issuances with similar remaining years to maturity, adjusted for credit risk, which represented a Level 3 measurement. For additional information on the Company's notes payable to related party, please read Note 8, Related Party Transactions, to these consolidated financial statements.

Research and Development Costs

Research and development costs are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries, stock-based compensation and benefits, facilities costs, depreciation, manufacturing expenses, and external costs of outside vendors engaged to conduct preclinical development activities and trials. Prior to initial regulatory approval, the Company expenses costs relating to the production of inventory for the Company's drug candidates, including ripretinib, as research and development expenses within the Company's consolidated statements of operations and comprehensive loss in the period incurred, unless the Company believes regulatory approval and subsequent commercialization of the drug candidate is probable and the Company expects the future economic benefit from sales of the drug to be realized.

Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses within the Company's consolidated balance sheets. The prepaid amounts are expensed as the related goods are delivered or the services are performed.

Research Contract Costs and Accruals

The Company has entered into various research and development contracts with research institutions and other companies both inside and outside of the U.S. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or trials, including the phase or completion of events, invoices received, and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company's estimates. The Company's historical accrual estimates have not been materially different from the actual costs.

Patent Costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as selling, general, and administrative expenses in the consolidated statements of operations and comprehensive loss.

Stock-Based Compensation

The Company measures all stock options and other stock-based awards granted to employees and directors based on the fair value on the date of the grant and recognizes compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. The straight-line method of expense recognition is applied to all awards with service-only conditions while the graded-vesting method is applied to all awards with both service and performance conditions. During 2019, the Company granted performance-based awards under which the fair market value of the awards is expensed after assessing the probability that certain performance criteria will be met and the associated targeted payout level that is forecasted will be achieved. The Company accounts for forfeitures as they occur.

The Company classifies stock-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient's payroll costs are classified or in which the award recipient's service payments are classified.

Income Taxes

Upon consummation of the Conversion on October 2, 2017, the Company became subject to corporate U.S. federal and state income taxes. Prior to the Conversion, the Company was treated as a partnership for income tax purposes and was not subject to U.S. federal or state income taxation. As a result, the Company had not recorded any U.S. federal or state income tax benefits prior to October 2, 2017 for the net losses incurred in each reporting period or for any earned research and orphan drug credits as the operating losses incurred by the Company had been passed through to its members.

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company's tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in its consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than- not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than

50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in stockholders' equity (deficit) that result from transactions and economic events other than those with shareholders. For the year ended December 31, 2019, the Company's other comprehensive income (loss) consisted of unrealized gains (losses) on marketable securities. For the years ended December 31, 2018 and 2017, there was no difference between net loss and comprehensive loss.

Net Loss per Share

Basic net income (loss) per share is computed by dividing the net income (loss) by the weighted average number of common shares outstanding for the years ended December 31, 2019, 2018, and 2017. Diluted net income (loss) per share is computed by dividing the diluted net income (loss) by the weighted average number of common shares, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted common stock, as determined using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per common share is the same as basic net loss per common share, since dilutive common shares are not assumed to have been issued if their effect is antidilutive.

The Company did not have any common shares outstanding during the period from January 1, 2017 through the closing of its initial public offering on October 2, 2017. To determine the weighted average shares outstanding for purpose of calculating net loss per share during those periods, the Company used the weighted average number of Series A convertible preferred shares outstanding because such shares represented the most subordinate share class outstanding during those periods. Share amounts for periods prior to the IPO have been retrospectively adjusted to give effect to the exchange of Series A convertible preferred shares into shares of common stock upon the Conversion. For additional information, please read Note 1, Nature of the Business and Basis of Presentation, to these consolidated financial statements.

Recently Adopted Accounting Pronouncements

Leases

In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-02, Leases (Topic 842) (ASU 2016-02).

ASU 2016-02 requires lessees to recognize leases on their balance sheet as a right-of-use asset and a lease liability as well as provide disclosures with respect to certain qualitative and quantitative information related to a company's leasing arrangements to meet the objective of allowing users of financial statements to assess the amount, timing, and uncertainty of cash flows arising from leases. Leases are classified as either operating or finance, and classification is based on criteria similar to current lease accounting, but without explicit bright lines. The guidance is effective for annual reporting periods beginning after December 15, 2018 and interim periods within those fiscal years, and early adoption is permitted. The FASB subsequently issued the following amendments to ASU 2016-02 that have the same effective date and transition date: ASU No. 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842, ASU No. 2018-10, Codification Improvements to Topic 842, Leases, ASU No. 2018-11, Leases (Topic 842): Targeted Improvements, ASU No. 2018-20, Narrow-Scope Improvement for Lessors, and ASU No. 2019-01, Leases (Topic 842): Codification Improvements. The Company adopted these amendments with ASU 2016-02 (collectively, the new leasing standards) effective January 1, 2019.

The Company adopted the new leasing standards using a modified retrospective approach, as of January 1, 2019, with no restatement of prior periods or cumulative adjustment to retained earnings. The Company elected the package of practical expedients, which permits the Company not to reassess under the new standards for prior conclusions about lease identification, lease classification and initial direct costs. The Company did not apply the hindsight practical expedient when determining the lease term for existing leases and assessing impairment of expired or existing leases. The Company elected the practical expedient for short-term leases and does not apply the recognition requirements to leases with a term of 12 months or less and recognizes those lease payments in the consolidated statements of operations and comprehensive loss on a straight-line basis over the lease term. The Company elected the practical expedient to not separate lease and non-lease components for real estate leases. The Company elected to utilize its incremental borrowing rate based on the remaining lease term as of the date of adoption.

In connection with the adoption, the Company recognized right-of-use assets of $0.8 million and lease liabilities of $0.8 million on its consolidated balance sheet. The underlying assets of the Company's leases consist of office and laboratory space. In addition, the Company reversed its build to suit asset of $11.9 million and related liabilities of $11.9 million because under the new leasing standards, the Company was no longer deemed the owner of the leased space. The adoption of the new leasing standards did not have a material impact on the Company's results of operations or cash flows. For additional information, please read Note 6, Leases, to these consolidated financial statements.

The Company accounts for a contract as a lease when it has the right to control the asset for a period of time while obtaining substantially all of the asset's economic benefits. The Company determines if an arrangement is a lease or contains an embedded lease at inception. For arrangements that meet the definition of a lease, the Company determines the initial classification and measurement of its operating right-of-use asset and operating lease liability at the lease commencement date and thereafter if modified. The lease term includes any renewal options that the Company is reasonably assured to exercise. The present value of lease payments is determined by using the interest rate implicit in the lease, if that rate is readily determinable; otherwise, the Company uses its estimated secured incremental borrowing rate for that lease term.

In addition to rent, the leases may require the Company to pay additional amounts for taxes, insurance, maintenance, and other expenses, which are generally referred to as non-lease components. The Company has elected to not separate lease and non-lease components. Only the fixed costs for lease components and their associated non-lease components are accounted for as a single lease component and recognized as part of a right-of-use asset and liability. Rent expense is recognized on a straight-line basis over the reasonably assured lease term based on the total lease payments and is included in operating expenses in the consolidated statements of operations and comprehensive loss.

Stock-Based Awards

In September 2018, the FASB issued ASU No. 2018-07, Compensation-Stock Compensation (Topic 718) – Improvements to Nonemployee Share-Based Payment Accounting (ASU 2018-07). This ASU is intended to simplify aspects of share-based compensation issued to non-employees by making the guidance consistent with the accounting for employee share-based compensation. The guidance is effective for annual reporting periods beginning after December 15, 2018 and interim periods within those fiscal years, and early adoption is permitted. The Company adopted ASU 2018-07 as of January 1, 2019, which had no impact on the Company's financial position, results of operations or cash flows.

License Agreement	12 Months Ended
License Agreement	Dec. 31, 2019
License Agreement [Abstract]
License Agreement	License Agreement Zai Lab (Shanghai) Co., Ltd. (Zai) License Agreement In June 2019, the Company entered into a License Agreement (the Zai License Agreement) with an affiliate of Zai Lab (Shanghai) Co., Ltd. (Zai), pursuant to which the Company granted Zai exclusive rights to develop and commercialize ripretinib, including certain follow-on compounds (the Licensed Products), in the Territory. The Company retains exclusive rights to, among other things, develop, manufacture, and commercialize the Licensed Products outside the Territory. Pursuant to the terms of the Zai License Agreement, the Company received an upfront cash payment of $20.0 million and became eligible to receive up to $185.0 million in potential development and commercial milestone payments, consisting of up to $50.0 million of development milestones and up to $135.0 million of commercial milestones. In addition, during the term of the Zai License Agreement, Zai will be obligated to pay the Company tiered percentage royalties ranging from low to high teens on potential annual net sales of the Licensed Products in the Territory, subject to adjustments in specified circumstances. Under the Zai License Agreement, the Company recognized revenue of $25.0 million during the year ended December 31, 2019, which consisted of the $20.0 million upfront payment and a $5.0 million INTRIGUE study-related development milestone payment, which the Company believed to be probable of achievement in the second quarter of 2019 and was achieved in July 2019. Subject to the terms and conditions of the Zai License Agreement, Zai will be responsible for conducting the development and commercialization activities in the Territory related to the Licensed Products. Subject to specified exceptions, during the term of the Zai License Agreement, each party has agreed that neither it nor its affiliates nor, with respect to Zai, its sublicensees, will conduct any development, manufacturing, and commercialization activities in the Territory that may be deemed competitive with the Licensed Products. In addition, under the Zai License Agreement, each party has granted the other party specified intellectual property licenses to enable the other party to perform its obligations and exercise its rights under the Zai License Agreement, including license grants to enable each party to conduct research, development and commercialization activities pursuant to the terms of the Zai License Agreement. The Company will supply or have supplied to Zai the Licensed Product pursuant to a supply agreement and for agreed upon consideration. The Zai License Agreement will continue on a Licensed Product-by-Licensed Product and region-by-region basis until the later of (i) the abandonment, expiry or final determination of invalidity of the last valid claim within the Company's patent rights that covers the Licensed Product in such region in the Territory; (ii) the expiry of the regulatory exclusivity for such Licensed Product in such region; or (iii) the close of business of the day that is exactly ten (10) years after the date of the first commercial sale of such Licensed Product in such region. Subject to the terms of the Zai License Agreement, Zai may terminate the Zai License Agreement for convenience by providing written notice to the Company, which termination will be effective following a prescribed notice period. In addition, the Company may terminate the Zai License Agreement under specified circumstances if Zai or certain other parties challenge our patent rights or if Zai or its affiliates do not conduct certain development activities with respect to one or more Licensed Products for a specified period of time, subject to specified exceptions. Either party may terminate the Zai License Agreement for the other party's uncured material breach of a material term of the Zai License Agreement, with a customary notice and cure period, or insolvency. After termination (but not natural expiration), the Company is entitled to retain a worldwide and perpetual license from Zai to exploit the Licensed Products. On a region-by-region and a Licensed Product-by-Licensed Product basis, upon the natural expiration of the Zai License Agreement as described above, the licenses granted by the Company to Zai under the Zai License Agreement in such region with respect to the Licensed Product become fully paid-up, perpetual and irrevocable. The Company identified the following promises under the Zai License Agreement: (1) the exclusive license, with the right to grant sublicenses, granted in the Territory for the Licensed Products; (2) initial and continuing know-how transfer for the Licensed Products; (3) clinical supply of the Licensed Products; (4) participation in the joint steering committee (JSC); and (5) regulatory and technical assistance responsibilities. The Company determined that the exclusive license is distinct and constitutes one performance obligation that is a right to use the Company's intellectual property. The Company determined that the promises under the Zai License Agreement related to the know-how transfer, clinical supply, participation in the JSC, and the assistance responsibilities are immaterial in the context of the Zai License Agreement and therefore are excluded from the assessment of performance obligations. The Company also evaluated certain options and contingent obligations contained within the Zai License Agreement to determine if they provide Zai with any material rights. The Company concluded that the options and contingent obligations were not issued at a significant and incremental discount, and therefore do not provide Zai with a material right. As such, these options and contingent obligations were excluded as performance obligations and will be accounted for if and when they occur or are exercised. The Company determined that the upfront payment of $20.0 million and the $5.0 million INTRIGUE study-related development milestone were probable of achievement and that a significant reversal of cumulative revenue would not occur upon resolution of the uncertainty, and constitutes the consideration to be included in the transaction price as of the commencement of the arrangement. The transaction price, totaling $25.0 million, was allocated to the one performance obligation, which was satisfied at a point in time upon delivery of the license in June 2019, and therefore the Company recognized license revenue in the full amount of the transaction price during the second quarter of 2019. The remaining potential milestone payments that the Company is eligible to receive were excluded from the transaction price and were fully constrained based on the probability of achievement. The Company will reevaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and if necessary, the Company will adjust its estimate of the transaction price. Because the performance obligation has been satisfied, any additions to the transaction price would be reflected in the period as a cumulative revenue catch-up. The Company assessed the Zai License Agreement to determine whether a significant financing component exists and concluded that a significant financing component does not exist.

Marketable Securities and Fair Value Measurements

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Marketable Securities and Fair Value Measurements

As of December 31, 2019, marketable securities by security type consisted of:


(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Commercial paper (due within one year)	$	314,292	$	74	$	(23)	$	314,343
U.S. Government securities (due within one year)	78,612		48		(3)		78,657
Certificates of deposit (due within one year)	66,241		17		(2)		66,256
Total	$	459,145	$	139	$	(28)	$	459,256

The Company had no marketable securities as of December 31, 2018.

The following tables present information about the Company's financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values:


As of December 31, 2019 (in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	28,192	$	—	$	28,192
Certificates of deposit	—		20,500		—		20,500
Marketable securities:
Commercial paper	—		314,343		—		314,343
U.S. Government securities	—		78,657		—		78,657
Certificates of deposit	—		66,256		—		66,256
Total	$	—	$	507,948	$	—	$	507,948


As of December 31, 2018 (in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	267,145	$	—	$	267,145
Total	$	—	$	267,145	$	—	$	267,145

The tables above exclude certificates of deposit of $1.5 million and $1.1 million as of December 31, 2019 and December 31, 2018, respectively, that the Company held to secure a letter of credit associated with a lease and to secure a credit card account in 2019. The certificates of deposit are measured at carrying value in the consolidated balance sheets in long-term investment—restricted and approximate fair value. For additional information on the letter of credit associated with a lease, please read Note 6, Leases, to these consolidated financial statements.

During the years ended December 31, 2019 and 2018, there were no transfers between Level 1, Level 2 and Level 3. The fair value of Level 2 instruments classified as cash equivalents and marketable securities were determined through third-party pricing services. The pricing services use many observable market inputs to determine value, including reportable trades, benchmark yields, credit spreads, broker/dealer quotes, bids, offers, current spot rates, and other industry and economic events.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Property and Equipment, Net

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

Property and equipment, net consisted of the following:


	December 31,
(in thousands)	2019		2018
Laboratory equipment	$	2,195	$	1,731
Computer equipment	2,950		465
Furniture and fixtures	1,941		201
Leasehold improvements	908		359
Construction in progress	169		11,914
Total cost	8,163		14,670
Less: Accumulated depreciation	(1,830)		(1,217)
Total property and equipment, net	$	6,333	$	13,453

Depreciation expense was $0.8 million, $0.3 million, and $0.2 million for the years ended December 31, 2019, 2018, and 2017, respectively.

For the year ended December 31, 2018, the construction in progress balance was related to the capitalization of leased space prior to the adoption of ASU 2016-02. For additional information, please read Note 6, Leases, to these consolidated financial statements.

Leases

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

Leases

The Company leases real estate, including office and laboratory space. During the year ended, and as of, December 31, 2019, there were no arrangements in which the Company was considered a lessor.

In May 2018, the Company entered into a lease for office space at 200 Smith Street in Waltham, Massachusetts (the Premises). The initial term of the lease expires in November 2029, unless terminated earlier in accordance with the terms of the lease. The Company is entitled to two five-year options to extend. The initial annual base rent is approximately $2.0 million and will increase annually for a total of $22.4 million over the lease term. The Company is obligated to pay its portion of real estate taxes and costs related to the premises, including costs of operations, maintenance, repair, replacement, and management of the new leased premises. The Company is required to maintain a cash balance of $1.1 million to secure a letter of credit associated with the lease. This amount was classified as long-term investment—restricted in the consolidated balance sheet as of December 31, 2019.

Prior to the adoption of ASU 2016-02, the Company was deemed to be the owner of this leased space during the construction period because of certain provisions within the lease agreement. As a result, as of December 31, 2018, the Company capitalized approximately $11.9 million (equal to the estimated cost of its leased portion of the premises) as construction-in-progress within property and equipment, net and recorded a corresponding build-to-suit facility lease financing obligation. Under ASU 2016-02, the Company was no longer considered the owner of the leased space and therefore the build-to suit asset and corresponding liabilities at December 31, 2018 were reversed as of the date of adoption on January 1, 2019 as the lease commencement date had not yet been met. In October 2019, the lease commencement date under ASU 2016-02 was met and resulted in the addition of an operating lease asset of $21.2 million and corresponding lease liability of $17.0 million in the fourth quarter of 2019. The Premises became the Company's new headquarters location in October 2019.

As of December 31, 2019, the Company had two five-year lease agreements for office and laboratory space in Lawrence, Kansas that began on January 1, 2016 and expire on December 31, 2020, and the Company had three leases for additional office space in Lawrence, Kansas that expire in December 2020. The lease agreements contain options to extend the lease terms however these extensions were not included in the right-of-use assets and lease liabilities as they were not reasonably certain of being exercised.

The Company is also currently subject to the remainder of a six-month lease extension that expires in March 2020 in Waltham, Massachusetts to accommodate short-term temporary needs, which was entered into during 2019. In addition, in August 2018, the Company entered into a nine-month sublease for additional temporary office space in Waltham, Massachusetts that expired in June 2019. The Company also had a three-year sublease agreement for office space in Waltham, Massachusetts that began in September 2016 and expired in September 2019. The expense related to these subleases are included in short-term lease costs for the year ended December 31, 2019.

The Company's leases require the Company to pay for certain operating expenses based on actual costs incurred and therefore, as the amounts are variable in nature, are expensed in the period incurred and included in variable lease costs for the year ended December 31, 2019. Payment escalations specified in the lease are recognized on a straight-line basis over the lease terms.

All of the Company's leases qualify as operating leases. The following table summarizes the presentation of the Company's operating leases in the consolidated balance sheet:


(in thousands)	As of December 31, 2019
Operating lease assets	$	21,158

Current operating lease liabilities	$	1,747
Operating lease liabilities, net of current portion	15,904
Total operating lease liabilities	$	17,651

The components of lease expense were as follows:


	Year Ended December 31,
(in thousands)	2019
Operating lease cost	$	1,223
Short-term lease cost	520
Variable lease cost	427
Total lease expense	$	2,170

Future annual minimum lease payments under operating leases are as follows:


(in thousands)	As of December 31, 2019
2020	$	2,646
2021	2,088
2022	2,132
2023	2,177
2024	2,221
Thereafter	11,562
Total future minimum lease payments	22,826
Less: imputed interest	(5,175)
Total operating lease liabilities	$	17,651

As previously disclosed in the Company's 2018 Annual Report on Form 10-K and under the previous lease accounting standard, ASC 840, Leases, the Company recorded rent expense of $1.1 million and $0.6 million during the years ended December 31, 2018 and 2017, respectively, and the following table summarizes the future minimum lease payments due under the operating leases as of December 31, 2018:


(in thousands)	As of December 31, 2018
2019	$	726
2020	333
Total	$	1,059

The weighted-average remaining lease term and weighted-average discount rate of the Company's operating leases are as follows:


	As of December 31, 2019
Weighted-average remaining lease term in years	9.63
Weighted-average discount rate	5.36	%

Supplemental disclosure of cash flow information related to the Company's operating leases included in cash flows used in operating activities in the consolidated statement of cash flows were as follows:


	Year Ended December 31,
(in thousands)	2019
Cash paid for amounts included in the measurement of operating lease liabilities	$	532
Operating lease liabilities arising from obtaining operating lease assets	$	17,144

In April 2019, the Company amended its lease for office space at the Premises to add an additional 38,003 square feet of space for a total of 82,346 square feet of space, which is expected to commence in the second quarter of 2020. The initial term of the lease for the additional space will expire in November 2029 unless terminated earlier in accordance with the terms of the lease and the Company is entitled to two five-year options to extend the lease. The initial annual base rent for the additional space is approximately $1.9 million and will increase annually for a total of $18.2 million over the lease term. The Company will be required to pay its share of operating expenses, taxes, and other expenses related to the additional leased premises. The Company will be required to increase the amount of cash to secure the letter of credit by $0.9 million upon substantial completion of the additional premises. As of December 31, 2019, the lease commencement date under ASU 2016-02 had not yet been met.

Accrued Expenses and Other Current Liabilities

12 Months Ended

Dec. 31, 2019

Payables and Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:


	December 31,
(in thousands)	2019		2018
External research and development expenses	$	20,462	$	8,761
Payroll and related expenses	12,902		4,139
Professional fees	3,810		747
Other	1,542		62
Total accrued expenses and other current liabilities	$	38,716	$	13,709

Related Party Transactions

12 Months Ended

Dec. 31, 2019

Related Party Transactions

8. Related Party Transactions

Clinical Reference Laboratory, Inc.

One of the members of the Company's board of directors was the Chief Executive Officer of Clinical Reference Laboratory, Inc. (CRL) during the years ended December 31, 2019, 2018, and 2017. CRL is owned by CHC, Inc., which owns

approximately 31% of Brightstar, a holder of more than 5% of the Company's common stock. The Company has entered into various agreements and transactions with CRL.

Notes Payable to Related Party

The Company was party to a loan agreement and a security agreement, each dated as of June 11, 2010, with CRL (the CRL Construction Loan). The Company borrowed an aggregate of $2.8 million under the loan agreement to finance improvements to the Company's biology and chemistry laboratories in Lawrence, Kansas. In December 2017, the loan was assigned to CHC, Inc., a related party, which owns 100% of CRL.

Borrowings under the loan bore interest at a fixed rate equal to 6.0% per annum and the Company was required to make monthly payments of principal and interest, based on a straight-line amortization schedule of 15 years, which commenced on January 1, 2011. For the years ended December 31, 2019, 2018, and 2017, the Company recorded $0.1 million of interest expense related to this loan. For the year ended December 31, 2019, the Company made $1.4 million in principal and interest payments under the loan and for the years ended December 31, 2018 and 2017, the Company made $0.3 million in principal and interest payments under the loan.

In December 2019, the Company repaid the outstanding balance of the loan, and as such, as of December 31, 2019, there were no principal amounts owed under the loan agreement. As of December 31, 2018, principal amounts owed under the loan agreement totaled $1.3 million as described in the table below:


(in thousands)	As of December 31, 2018
Notes payable to related party	$	1,294
Less: Current portion	(187)
Notes payable to related party, net of current portion	$	1,107

The CRL Construction Loan was collateralized by a security interest in all of the equipment and fixtures at the Company's laboratories in Lawrence, Kansas. Under the loan and security agreements, the Company agreed to affirmative, negative and financial covenants to which it remained subject until the loan was paid off in full. These covenants included limitations on the Company's ability to incur additional indebtedness and engage in certain fundamental business transactions, such as mergers or acquisitions of other businesses, as well as requirements that the Company comply with a maximum liabilities-to-assets ratio, a minimum working capital threshold, and a maximum debt-to-equity ratio. Events of default under the loan agreement included failure to make payments when due, insolvency events, failure to comply with covenants and material adverse effects with respect to the Company. The lender's remedies upon an event of default included the ability to accelerate all amounts that are due under the CRL Construction Loan to become immediately due and payable. As of December 31, 2019, the Company was no longer subject to such covenants, and as of December 31, 2018, the Company was in compliance with the financial covenants of the CRL Construction Loan.

Master Services Agreement with Related Party

The Company is party to a master services agreement, effective as of May 20, 2013, with CRL under which the Company purchased laboratory services. Under the agreement, the Company agreed to use CRL for laboratory testing needs. For the years ended December 31, 2019, 2018, and 2017, the Company recorded $0.7 million, $0.9 million, and $0.4 million, respectively, of research and development expense incurred under this agreement, of which $0.7 million, $0.8 million, and $0.4 million, respectively, was paid to CRL during those same periods. As of December 31, 2019 and 2018, total amounts owed to CRL for laboratory services were less than $0.1 million and $0.2 million, respectively, of which amounts were included in accounts payable and accrued expenses and other current liabilities in the consolidated balance sheets. The Company is not committed to purchase any minimum amounts under the agreement.

401(k) Plan with Related Party

In 2015, the Company entered into an agreement with CRL under which the Company became a participating employer in a defined contribution plan that was managed by CRL (the CRL 401(k) Plan). Effective January 1, 2018, the Company adopted the Deciphera Pharmaceuticals 401(k) Plan (the 2018 401(k) Plan) to which employees' and former employees' accounts were transitioned from the CRL 401(k) Plan. For the years ended December 31, 2019 and 2018, no contributions were made by employees of the Company to the CRL 401(k) Plan. For the year ended December 31, 2017, the total amount of contributions made by employees of the Company under the CRL 401(k) Plan was $0.6 million.

Convertible Preferred Shares	12 Months Ended
Convertible Preferred Shares	Dec. 31, 2019
Temporary Equity Disclosure [Abstract]
Convertible Preferred Shares	Convertible Preferred Shares Prior to the completion of its IPO in October 2017, the Company had outstanding Series A, Series B-1, Series B-2 and Series C convertible preferred shares. The Conversion included the exchange of all outstanding Series A, Series B and Series C preferred shares of Deciphera Pharmaceuticals, LLC for an aggregate of 24,425,190 shares of common stock of Deciphera Pharmaceuticals, Inc. For additional information on the IPO and conversion, please read Note 1, Nature of the Business and Basis of Presentation, to these consolidated financial statements. In May 2017, the Company entered into a Series C preferred shares purchase agreement, pursuant to which the Company sold 690,333 Series C Shares at a price of $75.76 per share for proceeds of $51.9 million, net of issuance costs of $0.4 million.

Common Stock	12 Months Ended
Common Stock	Dec. 31, 2019
Equity [Abstract]
Common Stock	Common Stock On October 2, 2017, immediately prior to the completion of the IPO, the Company engaged in a series of transactions whereby Deciphera Pharmaceuticals, LLC became a wholly owned subsidiary of Deciphera Pharmaceuticals, Inc. As part of the transactions, shareholders of Deciphera Pharmaceuticals, LLC exchanged their shares of Deciphera Pharmaceuticals, LLC for shares of Deciphera Pharmaceuticals, Inc. on a one-for-5.65 basis and exchanged their outstanding equity incentive awards of Deciphera Pharmaceuticals, LLC for options to purchase the same number of shares of common stock of Deciphera Pharmaceuticals, Inc. multiplied by 5.65, with a corresponding adjustment to divide the exercise price by 5.65 (the Conversion). The Conversion included the exchange of all outstanding series A, series B, and series C preferred shares of Deciphera Pharmaceuticals, LLC for an aggregate of 24,425,190 shares of common stock of Deciphera Pharmaceuticals, Inc. and the exchange of all outstanding options and share appreciations rights of Deciphera Pharmaceuticals, LLC for options to purchase common stock of Deciphera Pharmaceuticals, Inc. On October 2, 2017, Deciphera Pharmaceuticals, Inc., completed the IPO, pursuant to which it issued and sold 7,500,000 shares of common stock at the IPO price of $17.00 per share, resulting in net proceeds of $114.1 million after deducting underwriting discounts and commissions and other offering expenses. On October 4, 2017, the Company issued and sold an additional 666,496 shares of common stock at the IPO price of $17.00 per share pursuant to the underwriters' partial exercise of their option to purchase additional shares of common stock, resulting in additional net proceeds of $10.5 million after deducting underwriting discounts and commissions. Upon the closing of the IPO, the Company's outstanding convertible preferred shares automatically converted into shares of common stock. On June 11, 2018, the Company issued and sold 4,300,000 shares of its common stock in a follow-on public offering at a public offering price of $40.00 per share, resulting in net proceeds of $161.0 million after deducting underwriting discounts and commissions and other offering expenses. On June 20, 2018, the Company issued and sold an additional 645,000 shares of its common stock at the offering price of $40.00 per share, pursuant to the underwriters' full exercise of their option to purchase additional shares of common stock, resulting in additional net proceeds of $24.3 million after deducting underwriting discounts and commissions. On August 19, 2019, the Company issued and sold 10,810,810 shares of its common stock in a follow-on public offering at a public offering price of $37.00 per share, resulting in net proceeds of $375.4 million after deducting underwriting discounts and commissions and other offering expenses. On September 3, 2019, the Company issued and sold an additional 1,621,621 shares of its common stock at the offering price of $37.00 per share, pursuant to the underwriters' full exercise of their option to purchase additional shares of common stock, resulting in additional net proceeds of $56.4 million after deducting underwriting discounts and commissions. On February 19, 2020, the Company issued and sold 3,181,818 shares of its common stock in a follow-on public offering at a public offering price of $55.00 per share, resulting in net proceeds of $163.7 million after deducting underwriting discounts and commissions and other offering expenses. On February 25, 2020, the Company issued and sold an additional 477,272 shares of its common stock at the offering price of $55.00 per share, pursuant to the underwriters' full exercise of their option to purchase additional shares of common stock, resulting in additional net proceeds of $24.7 million after deducting underwriting discounts and commissions.

Stock-Based Awards

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Stock-Based Awards

2017 Equity Incentive Plan

The Company's 2017 Stock Option and Incentive Plan (the 2017 Plan) provides for the grant of equity-based incentive awards. The number of shares initially reserved for issuance of awards under the 2017 Plan was 2,655,831 shares of common stock and may be increased by the number of shares under the 2015 Equity Incentive Plan (the 2015 Plan) and the 2017 Plan

that are forfeited, cancelled, repurchased by the Company, or otherwise surrendered. The 2017 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1, beginning on January 1, 2018, by 4% of the outstanding number of shares of our common stock on the immediately preceding December 31, or such lesser number of shares as determined by the Compensation Committee of the Company's Board of Directors. As of December 31, 2019, 994,282 remained available for issuance under the 2017 Plan. The number of shares reserved for issuance under the 2017 Plan was increased by 2,064,706 shares effective January 1, 2020.

2015 Equity Incentive Plan

Under the 2015 Plan the Company was authorized to sell or issue common shares or restricted common shares, or to grant options for the purchase of common shares, share appreciation rights (SARs) and other awards, to employees, members of the board of directors, consultants, and advisors of the Company. Upon effectiveness of the 2017 Plan no further awards were available to be issued under the 2015 Plan.

Both the 2017 and 2015 Plans provide that they be administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The exercise prices for stock options may not be less than 100% of the fair market value of the common stock on the date of grant and the term of awards may not be greater than ten years. The Company bases fair value of common stock on the quoted market price. Vesting periods are determined at the discretion of the board of directors. Awards granted to employees and directors typically vest over four years.

2017 Employee Stock Purchase Plan

The 2017 Employee Stock Purchase Plan (the ESPP) initially reserved and authorized the issuance of up to 306,750 shares of common stock to participating employees. The ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2018 and each January 1 thereafter through January 1, 2027, by the least of (i) 1% of the outstanding number of shares of common stock on the immediately preceding December 31; (ii) 400,000; shares or (iii) such number of shares as determined by the ESPP administrator. As of December 31, 2019, 1,009,433 remained available for issuance under the ESPP Plan. The number of shares reserved for issuance under the ESPP was increased by 400,000 shares effective January 1, 2020.

As of December 31, 2019, no offering periods have commenced under the ESPP.

Stock Option Valuation

The fair value of each stock option award is estimated on the date of grant using the Black-Scholes option-pricing model, which uses as inputs the fair value of the Company's common stock and assumptions for the volatility of its common stock, the expected term of stock-based awards, the risk-free interest rate for a period that approximates the expected term of stock-based awards, and the expected dividend yield. Prior to October 2017, the Company was privately-held and lacked company-specific historical and implied volatility information. Therefore, it estimates its expected share volatility based on the historical volatility of a set of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The Company estimated the expected term of its options using the "simplified" method for awards that qualify as "plain-vanilla" options. For options that do not qualify as "plain-vanilla", the Company estimated the expected term using the average of vesting date and expiration date as it believes there is no better estimate of expected term. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends on common shares and does not expect to pay any cash dividends in the foreseeable future.

The assumptions that the Company used to determine the fair value of options granted to employees and directors were as follows, presented on a weighted average basis:


	Year Ended December 31,
	2019		2018		2017
Risk-free interest rate	2.2	%	2.8	%	1.9	%
Expected term (in years)	6.2		6.1		6.0
Expected volatility	74.5	%	73.3	%	78.3	%
Expected dividend yield	0	%	0	%	0	%

The following table summarizes the Company's option activity from January 1, 2019 to December 31, 2019:


	Number of Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2018	5,787,151	$	10.92
Granted	3,067,718	$	28.77
Exercised	(1,504,583)	$	4.49
Forfeited/Expired	(599,347)	$	23.40
Outstanding as of December 31, 2019	6,750,939	$	19.36	8.0	$	289,615
Options vested and expected to vest as of December 31, 2019	6,750,939	$	19.36	8.0	$	289,615
Options exercisable as of December 31, 2019	3,052,876	$	10.62	6.9	$	157,592

The aggregate intrinsic value of options is calculated as the difference between the exercise price of the options and the fair value of the Company's common shares for those options that had exercise prices lower than the fair value of the Company's common shares. The aggregate intrinsic value of options exercised during the years ended December 31, 2019 and 2018 was $53.2 million and $4.4 million, respectively. There were no option exercises during the year ended December 31, 2017.

The weighted average grant-date fair value per share of options granted during the years ended December 31, 2019, 2018, and 2017 was $19.22, $19.68, and $7.63, respectively.

Restricted Stock Units

The 2017 Plan provides for the award of restricted stock units. During 2019 and 2018, the Company granted restricted stock units to employees that were subject to time-based vesting conditions that lapse between one year and four years from date of grant, assuming continued employment.

During 2019, the Company also granted 57,400 restricted stock units at a weighted average grant date fair value of $34.43 that were subject to performance-based vesting conditions. Vesting of the performance-based restricted stock units are contingent upon meeting certain performance obligations and continued employment through the service period. No performance-based restricted units vested and no performance-based restricted units were forfeited during 2019.

All restricted stock units currently granted have been classified as equity instruments as their terms require settlement in shares. Restricted stock units with time-based and performance-based vesting conditions are valued on the grant date using the grant date market price of the underlying shares. The Company granted no performance-based restricted units in 2018 and granted no restricted stock units in 2017.

The table below summarizes the Company's time-based restricted stock unit activity from January 1, 2019 to December 31, 2019:


	Number of Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2018	25,000	$	33.43
Granted	87,000	$	29.03
Vested	(12,500)	$	33.43
Forfeited	—	$	—
Unvested at December 31, 2019	99,500	$	29.58

The fair value of time-based restricted stock units that vested during the year ended December 31, 2019 was $0.5 million. No restricted stock units vested during the years ended December 31, 2018 and 2017.

Stock-Based Compensation Expense

Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows:


	Year Ended December 31,
(in thousands)	2019		2018		2017
Research and development	$	7,934	$	4,021	$	1,320
Selling, general, and administrative	12,476		5,667		3,546
Total stock-based compensation	$	20,410	$	9,688	$	4,866

The following table summarizes share-based compensation expense associated with each of our share-based compensation arrangements:


	Year Ended December 31,
(in thousands)	2019		2018		2017
Stock options	$	19,328	$	9,578	$	4,866
Time-based restricted stock units	1,082		110		—
Total stock-based compensation expense	$	20,410	$	9,688	$	4,866

As of December 31, 2019, total unrecognized compensation cost related to the unvested share-based awards was $60.8 million, which is expected to be recognized over a weighted average of 2.7 years.

During the year ended December 31, 2019, the Company recorded $2.4 million of stock-based compensation expense related to the modification of stock options pursuant to the transition agreement with its former President and Chief Executive Officer, which was classified within selling, general, and administrative expenses in the statements of operations and comprehensive loss.

As of December 31, 2019, no expenses had been incurred related to performance-based restricted stock awards as the achievement of the related performance criteria was not probable.

401(k) Savings Plan	12 Months Ended
401(k) Savings Plan	Dec. 31, 2019
Retirement Benefits [Abstract]
401(k) Savings Plan	401(k) Savings Plan Effective January 1, 2018, the Company adopted the 2018 401(k) Plan, a defined contribution plan under Section 401(k) of the Internal Revenue Code, whereby the Company provides matching contributions of 100% of each employee's contribution up to a maximum matching contribution of 3% of the employee's eligible compensation and at a rate of 50% of each employee's contribution in excess of 3% up to a maximum of 5% of the employee's eligible compensation. Prior to January 1, 2018, the Company had a defined contribution plan that was managed by the CRL 401(k) Plan. Effective January 1, 2018, employees' and former employees' accounts were transitioned from the CRL 401(k) Plan to the 2018 401(k) Plan. Under the CRL 401(k) Plan, the Company provided matching contributions up to 50% of actual dollars contributed, not to exceed a maximum of 6% of gross wages, subject to certain time-based vesting requirements. Total employer matching contributions related to these plans were $0.9 million, $0.4 million, and $0.1 million respectively, for the years ended December 31, 2019, 2018, and 2017.

Net Loss per Share

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Net Loss per Share

Basic and diluted net loss per share was calculated as follows:


	Year Ended December 31,
(in thousands, except share and per share amounts)	2019		2018		2017
Numerator:
Net loss	$	(192,256)	$	(99,854)	$	(50,284)
Denominator:
Weighted average common shares outstanding—basic and diluted	42,869,058		35,390,480		16,792,179
Net loss per share—basic and diluted	$	(4.48)	$	(2.82)	$	(2.99)

On October 2, 2017, in connection with the closing of the IPO, all outstanding convertible preferred shares of Deciphera Pharmaceuticals, LLC were exchanged for shares of common stock of Deciphera Pharmaceuticals, Inc. upon the Conversion. For additional information, please read Note 1, Nature of the Business and Basis of Presentation, to these consolidated financial statements. In addition, because the Company had a net loss in each of the periods presented, diluted net loss per share attributable to common shareholders has not been presented as the effect of including common share equivalents in the calculations would have had an anti-dilutive impact.

The Company did not have any common shares outstanding during the period from January 1, 2017 through the closing of its initial public offering on October 2, 2017. Because the Series A convertible preferred shares represented the most subordinate share class outstanding during that period, in determining weighted average common shares outstanding for purposes of calculating net loss per share for periods prior to the IPO, the Company utilized Series A convertible preferred shares. Such shares have also been retrospectively adjusted to give effect to the exchange of Series A convertible preferred shares into shares of common stock upon the Conversion.

Common Stock Equivalents

The following potential dilutive securities, presented based on amounts outstanding at the end of each reporting period, have been excluded from the calculation of diluted net loss per share because including them would have had an anti-dilutive impact:


	As of December 31,
	2019	2018	2017
Options to purchase common stock	6,750,939	5,787,151	4,598,352
Unvested time-based restricted common stock units	99,500	25,000	—
Unvested performance-based restricted common stock units	57,400	—	—
Total	6,907,839	5,812,151	4,598,352

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

Prior to the Conversion in October 2017, the Company had been treated as a partnership for tax purposes and had not been subject to U.S. federal or state income taxation. As a result, the Company had not recorded any U.S. federal or state income tax benefits for the net losses incurred prior to October 2017 or for earned research and orphan drug credits. Upon the Conversion in October 2017, the Company became subject to Corporate U.S. federal and state income taxes.

During the years ended December 31, 2019 and 2018, and the period from October 2, 2017 to December 31, 2017, the Company recorded no income tax benefits for the net operating losses, due to its uncertainty of realizing a benefit from those items.

A reconciliation of the U.S. federal statutory income tax rate to the Company's effective income tax rate is as follows:


	Year Ended December 31,
	2019		2018		2017
Federal statutory income tax rate	21.0	%	21.0	%	34.0	%
State taxes, net of federal benefit	7.0		6.1		1.6
Research and orphan drug credit	5.4		9.6		7.7
Research and orphan drug credit addback	—		—		(6.6)
Impact of change in tax status	—		—		(8.7)
Effect of federal tax law change	—		—		(6.1)
Permanent adjustments and other	3.8		0.7		(0.3)
Increase in deferred tax asset valuation allowance	(37.2)		(37.4)		(21.6)
Effective income tax rate	—	%	—	%	—	%

Net deferred tax assets consisted of the following:


	December 31,
(in thousands)	2019		2018
Deferred tax assets (liabilities):
Net operating loss carryforwards	$	85,632	$	28,906
Research and orphan drug credit carryforwards	25,267		13,457
Stock-based compensation	5,535		4,681
Accrued expenses	2,951		1,270
Operating lease liabilities	5,841		3,200
Operating lease assets	(5,515)		—
Property and equipment	—		(3,200)
Other	(64)		(123)
Total gross deferred tax assets	119,647		48,191
Valuation allowance	(119,647)		(48,191)
Net deferred tax assets	$	—	$	—

On December 22, 2017, the Tax Cuts and Jobs Act (TCJA) was signed into U.S. law. The TCJA includes a number of changes to existing tax law, including, among other things, a permanent reduction in the federal corporate income tax rate from a top marginal rate of 35% to a flat rate of 21%, effective as of January 1, 2018, as well as limitation of the deduction for net operating losses to 80% of annual taxable income and elimination of net operating loss carrybacks, in each case, for losses arising in taxable years beginning after December 31, 2018 (though any such net operating losses may be carried forward indefinitely).

The Company remeasured certain deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future. In December 2017, the SEC staff issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Job Act (SAB 118) which allowed the Company to record provisional amounts during a measurement period not to extend beyond one year of the enactment date. The provisional amount was finalized during the year ended December 31, 2018, and did not result in a material change to the amount previously recorded. Due to the corresponding valuation allowance fully offsetting deferred taxes, there was no impact to the statement of operations and comprehensive loss.

The change in the valuation allowance was as follows:


	Year Ended December 31,
(in thousands)	2019		2018
Valuation allowance as of beginning of year	$	(48,191)	$	(10,835)
Net increases recorded to income tax provision	(71,456)		(37,356)
Valuation allowance as of end of year	$	(119,647)	$	(48,191)

As of December 31, 2019, the Company had net operating loss carryforwards for federal income tax purposes of $324.2 million, of which $14.5 million begin to expire in 2037 and $309.7 million may be carried forward indefinitely. As of December 31, 2019, the Company had net operating loss carryforwards for state income tax purposes of $288.6 million, which begin to expire in 2037. As of December 31, 2019, the Company also had available research and orphan drug credit carryforwards for federal and state income tax purposes of $23.1 million and $2.8 million, respectively, which begin to expire in 2037 and 2032, respectively. Utilization of the net operating loss carryforwards and research and orphan drug credit

carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986, as amended (the Code), and similar state law due to ownership changes that have occurred previously or that could occur in the future.

These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. The Company has not conducted a formal study to assess whether a change of control has occurred or whether there have been multiple changes of control since the IPO due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382 of the Code and similar state law, at any time since the IPO, utilization of the net operating loss carryforwards or research and orphan drug credit carryforwards may be subject to an annual limitation under Section 382 of the Code, which is determined by first multiplying the value of the Company's stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and orphan drug credit carryforwards before utilization.

The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company's history of cumulative net losses incurred since inception and its lack of commercialization of any products since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the deferred tax assets as of December 31, 2019. Management reevaluates the positive and negative evidence at each reporting period.

The Company has not recorded any amounts for unrecognized tax benefits as of December 31, 2019. The Company will recognize interest and penalties related to uncertain tax positions in income tax expense when, if ever, it is in a taxable income position. As of December 31, 2019 and 2018, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company's statement of operations and comprehensive loss.

The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending income tax examinations. The Company's tax years that are open under statute are from October 2, 2017 to the present. The Company's policy is to record interest and penalties related to income taxes as part of its income tax provision.

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies KBA Grants Prior to 2014, the Company received funding from two research and development grants from the KBA totaling $2.0 million and no further amounts will be received under these grants. Pursuant to Kansas law, the Company may be required to repay some or all of the financial assistance received from the KBA, subject to the discretion of the KBA, if the Company relocates the operations in which the KBA invested outside of the State of Kansas, if the Company initiates procedures to dissolve and wind up or cease operations within ten years after receiving such financial assistance, or upon certain significant changes to ownership of the Company. If any of these stipulations occur before 2024, the Company may be required to repay some or all of the financial assistance received. The Company will only account for the repayment of the grants if it becomes probable that the Company will be required to repay any funds previously received. Letter of Credit Associated with Lease In April 2019, the Company amended its lease for office space at the Premises, which will require the Company to increase the amount of cash to secure its letter of credit upon substantial completion of the additional premises. For additional information, please read Note 6, Leases, to these consolidated financial statements. As of December 31, 2019, the Company had not been required to increase the amount of cash related to the letter of credit. Legal Proceedings The Company is not currently a party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses the costs related to its legal proceedings as they are incurred. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners, and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and senior management that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not aware of any claims under indemnification arrangements, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of December 31, 2019 or 2018.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Data [Abstract]

Selected Quarterly Financial Data (Unaudited)

The following information has been derived from unaudited consolidated financial statements that, in the opinion of management, include all recurring adjustments necessary for a fair statement of such information:


	Three Months Ended
(in thousands except per share data)	Dec 31, 2019		Sep 30, 2019		Jun 30, 2019		Mar 31, 2019		Dec 31, 2018		Sep 30, 2018		Jun 30, 2018		Mar 31, 2018
Statements of Operations Data:
Revenues	$	—	$	—	$	25,000	$	—	$	—	$	—	$	—	$	—
Loss from operations	(70,373)		(58,353)		(22,975)		(49,025)		(33,830)		(25,889)		(22,429)		(21,951)
Net loss	(67,216)		(56,196)		(21,460)		(47,384)		(32,299)		(24,435)		(21,690)		(21,430)
Net loss per share—basic and diluted	$	(1.31)	$	(1.28)	$	(0.56)	$	(1.25)	$	(0.86)	$	(0.65)	$	(0.65)	$	(0.66)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

The Company considers all highly liquid investments with original maturities of 90 days or less at the date of purchase to be cash equivalents.

Marketable Securities

Concentrations of Credit Risk and of Significant Suppliers

Long-Term Investment-Restricted

Long-Term Investment—Restricted

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset as follows:


Asset Category			Estimated Useful Life
Lab equipment			5 to 7 years
Computer equipment			3 to 5 years
Furniture and fixtures			7 years
Leasehold improvements			Shorter of life of lease or 15 years

Impairment of Long-Lived Assets

Fair Value Measurements

•Level 1—Quoted prices in active markets for identical assets or liabilities.

Research and Development Costs

Research Contract Costs and Accruals

Patent Costs

Stock-Based Compensation

Income Taxes

Comprehensive Loss

Net Loss per Share

Recently Adopted Accounting Pronouncements

Leases

In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-02, Leases (Topic 842) (ASU 2016-02).

Stock-Based Awards

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Estimated Useful life of Assets

Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset as follows:


Asset Category			Estimated Useful Life
Lab equipment			5 to 7 years
Computer equipment			3 to 5 years
Furniture and fixtures			7 years
Leasehold improvements			Shorter of life of lease or 15 years

Marketable Securities and Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Schedule of Marketable Securities

As of December 31, 2019, marketable securities by security type consisted of:


(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Commercial paper (due within one year)	$	314,292	$	74	$	(23)	$	314,343
U.S. Government securities (due within one year)	78,612		48		(3)		78,657
Certificates of deposit (due within one year)	66,241		17		(2)		66,256
Total	$	459,145	$	139	$	(28)	$	459,256

Schedule of Financial Assets Measured at Fair Value on a Recurring Basis


As of December 31, 2019 (in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	28,192	$	—	$	28,192
Certificates of deposit	—		20,500		—		20,500
Marketable securities:
Commercial paper	—		314,343		—		314,343
U.S. Government securities	—		78,657		—		78,657
Certificates of deposit	—		66,256		—		66,256
Total	$	—	$	507,948	$	—	$	507,948


As of December 31, 2018 (in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	267,145	$	—	$	267,145
Total	$	—	$	267,145	$	—	$	267,145

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

Summary of Property and Equipment, Net

Property and equipment, net consisted of the following:


	December 31,
(in thousands)	2019		2018
Laboratory equipment	$	2,195	$	1,731
Computer equipment	2,950		465
Furniture and fixtures	1,941		201
Leasehold improvements	908		359
Construction in progress	169		11,914
Total cost	8,163		14,670
Less: Accumulated depreciation	(1,830)		(1,217)
Total property and equipment, net	$	6,333	$	13,453

Leases (Tables)

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

Operating Leases in the Consolidated Balance Sheet and Weight-Average Remaining Lease Term and Discount Rate

All of the Company's leases qualify as operating leases. The following table summarizes the presentation of the Company's operating leases in the consolidated balance sheet:


(in thousands)	As of December 31, 2019
Operating lease assets	$	21,158

Current operating lease liabilities	$	1,747
Operating lease liabilities, net of current portion	15,904
Total operating lease liabilities	$	17,651

The weighted-average remaining lease term and weighted-average discount rate of the Company's operating leases are as follows:


	As of December 31, 2019
Weighted-average remaining lease term in years	9.63
Weighted-average discount rate	5.36	%

Components of Lease Expense and Supplemental Cash Flow Information

The components of lease expense were as follows:


	Year Ended December 31,
(in thousands)	2019
Operating lease cost	$	1,223
Short-term lease cost	520
Variable lease cost	427
Total lease expense	$	2,170


	Year Ended December 31,
(in thousands)	2019
Cash paid for amounts included in the measurement of operating lease liabilities	$	532
Operating lease liabilities arising from obtaining operating lease assets	$	17,144

Summary of Future Annual Minimum Lease Payments Under Operating Leases

Future annual minimum lease payments under operating leases are as follows:


(in thousands)	As of December 31, 2019
2020	$	2,646
2021	2,088
2022	2,132
2023	2,177
2024	2,221
Thereafter	11,562
Total future minimum lease payments	22,826
Less: imputed interest	(5,175)
Total operating lease liabilities	$	17,651

Summary of Future Minimum Lease Payments under Operating Leases


(in thousands)	As of December 31, 2018
2019	$	726
2020	333
Total	$	1,059

Accrued Expenses and Other Current Liabilities (Tables)

12 Months Ended

Dec. 31, 2019

Payables and Accruals [Abstract]

Schedule of Accrued Expenses


	December 31,
(in thousands)	2019		2018
External research and development expenses	$	20,462	$	8,761
Payroll and related expenses	12,902		4,139
Professional fees	3,810		747
Other	1,542		62
Total accrued expenses and other current liabilities	$	38,716	$	13,709

Related Party Disclosures (Tables)

12 Months Ended

Dec. 31, 2019

Schedule of Notes Payable to Related Party

As of December 31, 2018, principal amounts owed under the loan agreement totaled $1.3 million as described in the table below:


(in thousands)	As of December 31, 2018
Notes payable to related party	$	1,294
Less: Current portion	(187)
Notes payable to related party, net of current portion	$	1,107

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Summary of Assumptions used to Determine the Fair Value of Options Granted to Employees and Directors

The assumptions that the Company used to determine the fair value of options granted to employees and directors were as follows, presented on a weighted average basis:


	Year Ended December 31,
	2019		2018		2017
Risk-free interest rate	2.2	%	2.8	%	1.9	%
Expected term (in years)	6.2		6.1		6.0
Expected volatility	74.5	%	73.3	%	78.3	%
Expected dividend yield	0	%	0	%	0	%

Summary of Option Activity

The following table summarizes the Company's option activity from January 1, 2019 to December 31, 2019:


	Number of Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2018	5,787,151	$	10.92
Granted	3,067,718	$	28.77
Exercised	(1,504,583)	$	4.49
Forfeited/Expired	(599,347)	$	23.40
Outstanding as of December 31, 2019	6,750,939	$	19.36	8.0	$	289,615
Options vested and expected to vest as of December 31, 2019	6,750,939	$	19.36	8.0	$	289,615
Options exercisable as of December 31, 2019	3,052,876	$	10.62	6.9	$	157,592

Summary of RSU Activity

The table below summarizes the Company's time-based restricted stock unit activity from January 1, 2019 to December 31, 2019:


	Number of Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2018	25,000	$	33.43
Granted	87,000	$	29.03
Vested	(12,500)	$	33.43
Forfeited	—	$	—
Unvested at December 31, 2019	99,500	$	29.58

Classification of Stock-Based Compensation Expense

Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows:


	Year Ended December 31,
(in thousands)	2019		2018		2017
Research and development	$	7,934	$	4,021	$	1,320
Selling, general, and administrative	12,476		5,667		3,546
Total stock-based compensation	$	20,410	$	9,688	$	4,866

The following table summarizes share-based compensation expense associated with each of our share-based compensation arrangements:


	Year Ended December 31,
(in thousands)	2019		2018		2017
Stock options	$	19,328	$	9,578	$	4,866
Time-based restricted stock units	1,082		110		—
Total stock-based compensation expense	$	20,410	$	9,688	$	4,866

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Summary of Basic and Diluted Net Loss per Share

Basic and diluted net loss per share was calculated as follows:


	Year Ended December 31,
(in thousands, except share and per share amounts)	2019		2018		2017
Numerator:
Net loss	$	(192,256)	$	(99,854)	$	(50,284)
Denominator:
Weighted average common shares outstanding—basic and diluted	42,869,058		35,390,480		16,792,179
Net loss per share—basic and diluted	$	(4.48)	$	(2.82)	$	(2.99)

Summary of Potential Dilutive Securities


	As of December 31,
	2019	2018	2017
Options to purchase common stock	6,750,939	5,787,151	4,598,352
Unvested time-based restricted common stock units	99,500	25,000	—
Unvested performance-based restricted common stock units	57,400	—	—
Total	6,907,839	5,812,151	4,598,352

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Reconciliation of U.S. Federal Statutory Income Tax Rate to Effective Income Tax Rate

A reconciliation of the U.S. federal statutory income tax rate to the Company's effective income tax rate is as follows:


	Year Ended December 31,
	2019		2018		2017
Federal statutory income tax rate	21.0	%	21.0	%	34.0	%
State taxes, net of federal benefit	7.0		6.1		1.6
Research and orphan drug credit	5.4		9.6		7.7
Research and orphan drug credit addback	—		—		(6.6)
Impact of change in tax status	—		—		(8.7)
Effect of federal tax law change	—		—		(6.1)
Permanent adjustments and other	3.8		0.7		(0.3)
Increase in deferred tax asset valuation allowance	(37.2)		(37.4)		(21.6)
Effective income tax rate	—	%	—	%	—	%

Schedule of Net Deferred Tax Assets

Net deferred tax assets consisted of the following:


	December 31,
(in thousands)	2019		2018
Deferred tax assets (liabilities):
Net operating loss carryforwards	$	85,632	$	28,906
Research and orphan drug credit carryforwards	25,267		13,457
Stock-based compensation	5,535		4,681
Accrued expenses	2,951		1,270
Operating lease liabilities	5,841		3,200
Operating lease assets	(5,515)		—
Property and equipment	—		(3,200)
Other	(64)		(123)
Total gross deferred tax assets	119,647		48,191
Valuation allowance	(119,647)		(48,191)
Net deferred tax assets	$	—	$	—

Schedule of Changes in Valuation Allowance for Deferred Tax Assets

The change in the valuation allowance was as follows:


	Year Ended December 31,
(in thousands)	2019		2018
Valuation allowance as of beginning of year	$	(48,191)	$	(10,835)
Net increases recorded to income tax provision	(71,456)		(37,356)
Valuation allowance as of end of year	$	(119,647)	$	(48,191)

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Data [Abstract]

Schedule of Selected Quarterly Financial Data


	Three Months Ended
(in thousands except per share data)	Dec 31, 2019		Sep 30, 2019		Jun 30, 2019		Mar 31, 2019		Dec 31, 2018		Sep 30, 2018		Jun 30, 2018		Mar 31, 2018
Statements of Operations Data:
Revenues	$	—	$	—	$	25,000	$	—	$	—	$	—	$	—	$	—
Loss from operations	(70,373)		(58,353)		(22,975)		(49,025)		(33,830)		(25,889)		(22,429)		(21,951)
Net loss	(67,216)		(56,196)		(21,460)		(47,384)		(32,299)		(24,435)		(21,690)		(21,430)
Net loss per share—basic and diluted	$	(1.31)	$	(1.28)	$	(0.56)	$	(1.25)	$	(0.86)	$	(0.65)	$	(0.65)	$	(0.66)

Nature of the Business and Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Thousands								1 Months Ended			3 Months Ended								12 Months Ended
	Feb. 25, 2020 USD ($) $ / shares shares	Feb. 19, 2020 USD ($) $ / shares shares	Sep. 03, 2019 USD ($) $ / shares shares	Aug. 19, 2019 USD ($) $ / shares shares	Jun. 20, 2018 USD ($) $ / shares shares	Jun. 11, 2018 USD ($) $ / shares shares	Oct. 02, 2017 USD ($) $ / shares shares	Feb. 29, 2020 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	Oct. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares
Nature Of Business And Basis Of Presentation [Line Items]
Share conversion ratio							5.65
Net loss											$ (67,216)	$ (56,196)	$ (21,460)	$ (47,384)	$ (32,299)	$ (24,435)	$ (21,690)	$ (21,430)	$ (192,256)	$ (99,854)	$ (50,284)
Accumulated deficit											(487,979)				$ (295,723)				(487,979)	$ (295,723)
Cash, cash equivalents and marketable securities											$ 579,600								$ 579,600
Common Shares
Nature Of Business And Basis Of Presentation [Line Items]
Issuance of common stock sold in public offering, net of underwriting discounts, commissions and offering costs (in shares) \| shares																			12,432,431	4,945,000	8,166,496
IPO
Nature Of Business And Basis Of Presentation [Line Items]
Issuance of common stock sold in public offering, net of underwriting discounts, commissions and offering costs (in shares) \| shares							7,500,000			8,166,496
Additional offering price of common stock (in dollars per share) \| $ / shares										$ 17.00
Net proceeds from initial public offering							$ 114,100			$ 124,600
IPO \| Common Shares
Nature Of Business And Basis Of Presentation [Line Items]
Additional offering price of common stock (in dollars per share) \| $ / shares							$ 17.00
Follow On Offering \| Common Shares
Nature Of Business And Basis Of Presentation [Line Items]
Issuance of common stock sold in public offering, net of underwriting discounts, commissions and offering costs (in shares) \| shares			1,621,621	10,810,810	645,000	4,300,000			4,945,000			12,432,431
Additional offering price of common stock (in dollars per share) \| $ / shares			$ 37.00	$ 37.00	$ 40.00	$ 40.00			$ 40.00			$ 37.00					$ 40.00
Net proceeds from initial public offering			$ 56,400	$ 375,400	$ 24,300	$ 161,000			$ 185,300			$ 431,800
Follow On Offering \| Common Shares \| Subsequent Event
Nature Of Business And Basis Of Presentation [Line Items]
Issuance of common stock sold in public offering, net of underwriting discounts, commissions and offering costs (in shares) \| shares	477,272	3,181,818						3,659,090
Additional offering price of common stock (in dollars per share) \| $ / shares	$ 55.00	$ 55.00						$ 55.00
Net proceeds from initial public offering	$ 24,700	$ 163,700						$ 188,400

Summary of Significant Accounting Policies - Summary of Estimated Useful life of Assets (Details)	12 Months Ended
	Dec. 31, 2019
Lab equipment \| Minimum
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful lives	5 years
Lab equipment \| Maximum
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful lives	7 years
Computer equipment \| Minimum
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful lives	3 years
Computer equipment \| Maximum
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful lives	5 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful lives	7 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful lives	Shorter of life of leaseor 15 years

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Oct. 31, 2019	Jan. 01, 2019
Significant Accounting Policies [Line Items]
Impairment losses on long-lived assets	$ 0	$ 0	$ 0
Common stock, shares outstanding (in shares)	51,617,639	37,676,760
Operating lease assets	$ 21,158,000	$ 0
Total operating lease liabilities	17,651,000				$ 11,900,000
Build to suit asset	$ 8,163,000	14,670,000
Minimum
Significant Accounting Policies [Line Items]
Income tax examination, likelihood percentage	50.00%
Construction in progress
Significant Accounting Policies [Line Items]
Build to suit asset	$ 169,000	11,914,000			11,900,000
Accounting Standards Update 2016-02
Significant Accounting Policies [Line Items]
Operating lease assets				$ 21,200,000	800,000
Total operating lease liabilities				$ 17,000,000.0	$ 800,000
CRL Construction Loan
Significant Accounting Policies [Line Items]
Fair value of outstanding notes payable to related party		$ 1,100,000

License Agreement - Additional Information (Details) - Zai License Agreement - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2019
License Agreement Transactions [Line Items]
Upfront cash payment receivable	$ 20.0	$ 20.0
Agreement continuation period	10 years
Upfront payment recognized revenue			$ 20.0
License
License Agreement Transactions [Line Items]
Revenues			$ 25.0
Development And Commercial Milestone \| Maximum
License Agreement Transactions [Line Items]
License agreement milestone	$ 185.0
Development Milestone \| INTRIGUE Study Related Milestone
License Agreement Transactions [Line Items]
License agreement milestone		5.0
Development Milestone \| Maximum
License Agreement Transactions [Line Items]
License agreement milestone	50.0
Commercial Milestone \| Maximum
License Agreement Transactions [Line Items]
License agreement milestone	$ 135.0
Development And Regulatory Milestone
License Agreement Transactions [Line Items]
License agreement milestone		$ 5.0

Marketable Securities and Fair Value Measurements - Schedule of Marketable Securities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Marketable Securities [Line Items]
Amortized Cost	$ 459,145,000
Gross Unrealized Gains	139,000
Gross Unrealized Losses	(28,000)
Estimated Fair Value	459,256,000	$ 0
Commercial paper
Marketable Securities [Line Items]
Amortized Cost	314,292,000
Gross Unrealized Gains	74,000
Gross Unrealized Losses	(23,000)
Estimated Fair Value	314,343,000
U.S. Government securities
Marketable Securities [Line Items]
Amortized Cost	78,612,000
Gross Unrealized Gains	48,000
Gross Unrealized Losses	(3,000)
Estimated Fair Value	78,657,000
Certificates of deposit
Marketable Securities [Line Items]
Amortized Cost	66,241,000
Gross Unrealized Gains	17,000
Gross Unrealized Losses	(2,000)
Estimated Fair Value	$ 66,256,000

Marketable Securities and Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	May 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	$ 459,256,000	$ 0
Transfers between Level 1, Level 2 and Level 3	0	0
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	66,256,000
Certificates of deposit \| Letter of Credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash balance held to secure letter of credit associated with lease	$ 1,500,000	$ 1,100,000	$ 1,100,000

Marketable Securities and Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Cash equivalents:
Total Cash equivalents		$ 267,145,000
Marketable securities:
Total Marketable securities	$ 459,256,000	0
Assets, Fair Value Disclosure	507,948,000
U.S. Government securities
Marketable securities:
Total Marketable securities	78,657,000
Money market funds
Cash equivalents:
Total Cash equivalents	28,192,000	267,145,000
Certificates of deposit
Cash equivalents:
Total Cash equivalents	20,500,000
Marketable securities:
Total Marketable securities	66,256,000
Commercial paper
Marketable securities:
Total Marketable securities	314,343,000
Level 1
Cash equivalents:
Total Cash equivalents		0
Marketable securities:
Assets, Fair Value Disclosure	0
Level 1 \| U.S. Government securities
Marketable securities:
Total Marketable securities	0
Level 1 \| Money market funds
Cash equivalents:
Total Cash equivalents	0	0
Level 1 \| Certificates of deposit
Cash equivalents:
Total Cash equivalents	0
Marketable securities:
Total Marketable securities	0
Level 1 \| Commercial paper
Marketable securities:
Total Marketable securities	0
Level 2
Cash equivalents:
Total Cash equivalents		267,145,000
Marketable securities:
Assets, Fair Value Disclosure	507,948,000
Level 2 \| U.S. Government securities
Marketable securities:
Total Marketable securities	78,657,000
Level 2 \| Money market funds
Cash equivalents:
Total Cash equivalents	28,192,000	267,145,000
Level 2 \| Certificates of deposit
Cash equivalents:
Total Cash equivalents	20,500,000
Marketable securities:
Total Marketable securities	66,256,000
Level 2 \| Commercial paper
Marketable securities:
Total Marketable securities	314,343,000
Level 3
Cash equivalents:
Total Cash equivalents		0
Marketable securities:
Assets, Fair Value Disclosure	0
Level 3 \| U.S. Government securities
Marketable securities:
Total Marketable securities	0
Level 3 \| Money market funds
Cash equivalents:
Total Cash equivalents	0	$ 0
Level 3 \| Certificates of deposit
Cash equivalents:
Total Cash equivalents	0
Marketable securities:
Total Marketable securities	0
Level 3 \| Commercial paper
Marketable securities:
Total Marketable securities	$ 0

Property and Equipment, Net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total cost	$ 8,163		$ 14,670
Less: Accumulated depreciation	(1,830)		(1,217)
Total property and equipment, net	6,333		13,453
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total cost	2,195		1,731
Computer equipment
Property, Plant and Equipment [Line Items]
Total cost	2,950		465
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total cost	1,941		201
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total cost	908		359
Construction in progress
Property, Plant and Equipment [Line Items]
Total cost	$ 169	$ 11,900	$ 11,914

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 830	$ 317	$ 150

Leases - Operating Leases in the Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease assets	$ 21,158		$ 0
Operating lease liabilities	1,747		539
Operating lease liabilities, net of current portion	15,904		$ 11,347
Total operating lease liabilities	$ 17,651	$ 11,900
Weighted-average remaining lease term in years	9 years 7 months 17 days
Weighted-average discount rate	5.36%

Leases - Components of Lease Expense (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Leases [Abstract]
Operating lease cost	$ 1,223
Short-term lease cost	520
Variable lease cost	427
Total lease expense	$ 2,170

Leases - Summary of Future Minimum Lease Payments under Operating Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Operating Leases, After Adoption
2020	$ 2,646
2021	2,088
2022	2,132
2023	2,177
2024	2,221
Thereafter	11,562
Total future minimum lease payments	22,826
Less: imputed interest	(5,175)
Total operating lease liabilities	$ 17,651	$ 11,900
Operating Leases, Before Adoption
2019			$ 726
2020			333
Future minimum lease payments due			$ 1,059

Leases - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Leases [Abstract]
Addition of operating lease asset included in accrued expenses and other current liabilities	$ 532	$ 562	$ 0	$ 0
Operating lease liabilities arising from obtaining operating lease assets	$ 17,144

Leases - Additional Information (Details) $ in Thousands	1 Months Ended			12 Months Ended
Leases - Additional Information (Details) $ in Thousands	Apr. 30, 2019 USD ($) ft²	Aug. 30, 2018	May 31, 2018 USD ($)	Dec. 31, 2019 USD ($) contract offering_period renewal_option	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Initial annual base rent	$ 1,900		$ 2,000
Initial annual base rent increase	$ 18,200		22,400
Amounts capitalized under build-to-suit lease transaction				$ 0	$ 11,885	$ 0
Rent expense					1,100	$ 600
Additional office space \| ft²	38,003
Operating lease area \| ft²	82,346
Operating lease assets				21,158	0
Total operating lease liabilities				$ 17,651				$ 11,900
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease assets							$ 21,200	800
Total operating lease liabilities							$ 17,000	$ 800
Massachusetts
Lessee, Lease, Description [Line Items]
Lease renewal term				5 years
Remainder of lease extension term				6 months
Sublease term		9 months		3 years
Number of lease options \| renewal_option				2
Kansas
Lessee, Lease, Description [Line Items]
Number of lease agreement \| contract				2
Term of lease agreements				5 years
Number of additional lease agreements \| offering_period				3
Certificates of deposit \| Letter of Credit
Lessee, Lease, Description [Line Items]
Cash balance held to secure letter of credit associated with lease			$ 1,100	$ 1,500	$ 1,100
Additional Amount \| Certificates of deposit
Lessee, Lease, Description [Line Items]
Cash balance held to secure letter of credit associated with lease	$ 900

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts Payable and Accrued Liabilities [Abstract]
External research and development expenses	$ 20,462	$ 8,761
Payroll and related expenses	12,902	4,139
Professional fees	3,810	747
Other	1,542	62
Total accrued expenses and other current liabilities	$ 38,716	$ 13,709

Related Party Transactions - Notes Payable to Related Party (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Less: Current portion	$ 0	$ (187)
Notes payable to related party, net of current portion	$ 0	1,107
CRL Construction Loan \| Clinical Reference Laboratory, Inc.
Related Party Transaction [Line Items]
Notes payable to related party		1,294
Less: Current portion		(187)
Notes payable to related party, net of current portion		$ 1,107

Related Party Transactions - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Research and development expense	$ 157,610,000	$ 82,887,000	$ 39,514,000
Brightstar \| CHC, Inc. \| Loan and Security Agreement
Related Party Transaction [Line Items]
Ownership percentage	31.00%
Clinical Reference Laboratory, Inc.
Related Party Transaction [Line Items]
Laboratory services	$ 100,000
Clinical Reference Laboratory, Inc. \| Loan and Security Agreement
Related Party Transaction [Line Items]
Principal amount owed under loan agreement	0	1,300,000
Clinical Reference Laboratory, Inc. \| Service Agreement
Related Party Transaction [Line Items]
Research and development expense	700,000	900,000	400,000
Payments for research and development expense	700,000	800,000	400,000
Laboratory services		200,000
Employees contributions under 401(K) plan	0	0	$ 600,000
Clinical Reference Laboratory, Inc. \| CHC, Inc. \| Loan and Security Agreement
Related Party Transaction [Line Items]
Ownership percentage			100.00%
Aggregate borrowings	$ 2,800,000
Fixed interest rate	6.00%
Debt instrument term	15 years
Interest expense on borrowings	$ 100,000	100,000	$ 100,000
Debt instrument principal and interest payment	$ 1,400,000
Principal amount owed under loan agreement		$ 300,000	$ 300,000
Clinical Reference Laboratory, Inc. \| Brightstar \| Minimum
Related Party Transaction [Line Items]
Percentage of common stock holding	5.00%

Convertible Preferred Shares - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Oct. 31, 2017	May 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Redeemable Noncontrolling Interest [Line Items]
Conversion of preferred stock to common stock (in shares)	24,425,190
Proceeds from issuance of convertible preferred shares			$ 0	$ 0	$ 52,300
Payments of convertible preferred share issuance costs			$ 0	$ 0	$ 429
Series C Convertible Preferred Shares
Redeemable Noncontrolling Interest [Line Items]
Number of convertible preferred shares sold under share purchase agreement (in shares)		690,333
Convertible preferred shares sold under share purchase agreement (in dollars per share)		$ 75.76
Proceeds from issuance of convertible preferred shares		$ 51,900
Payments of convertible preferred share issuance costs		$ 400

Common Stock - Additional Information (Details) $ / shares in Units, $ in Thousands									1 Months Ended			3 Months Ended	12 Months Ended
	Feb. 25, 2020 USD ($) $ / shares shares	Feb. 19, 2020 USD ($) $ / shares shares	Sep. 03, 2019 USD ($) $ / shares shares	Aug. 19, 2019 USD ($) $ / shares shares	Jun. 20, 2018 USD ($) $ / shares shares	Jun. 11, 2018 USD ($) $ / shares shares	Oct. 04, 2017 USD ($) $ / shares shares	Oct. 02, 2017 USD ($) $ / shares shares	Feb. 29, 2020 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	Oct. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares
Class of Stock [Line Items]
Share conversion ratio								5.65
Conversion of preferred stock to common stock (in shares)											24,425,190
Proceeds from additional offering of shares \| $													$ 432,400	$ 185,933	$ 129,112
Common Shares
Class of Stock [Line Items]
Number of additional shares issued and sold (in shares)													12,432,431	4,945,000	8,166,496
IPO
Class of Stock [Line Items]
Number of additional shares issued and sold (in shares)								7,500,000			8,166,496
Additional offering price of common stock (in dollars per share) \| $ / shares											$ 17.00
Net proceeds from initial public offering \| $								$ 114,100			$ 124,600
IPO \| Common Shares
Class of Stock [Line Items]
Conversion of preferred stock to common stock (in shares)								24,425,190
Additional offering price of common stock (in dollars per share) \| $ / shares								$ 17.00
Over-Allotment Option
Class of Stock [Line Items]
Number of additional shares issued and sold (in shares)							666,496
Proceeds from additional offering of shares \| $							$ 10,500
Over-Allotment Option \| Common Shares
Class of Stock [Line Items]
Additional offering price of common stock (in dollars per share) \| $ / shares							$ 17.00
Follow On Offering \| Common Shares
Class of Stock [Line Items]
Number of additional shares issued and sold (in shares)			1,621,621	10,810,810	645,000	4,300,000				4,945,000		12,432,431
Additional offering price of common stock (in dollars per share) \| $ / shares			$ 37.00	$ 37.00	$ 40.00	$ 40.00				$ 40.00		$ 37.00
Net proceeds from initial public offering \| $			$ 56,400	$ 375,400	$ 24,300	$ 161,000				$ 185,300		$ 431,800
Follow On Offering \| Common Shares \| Subsequent Event
Class of Stock [Line Items]
Number of additional shares issued and sold (in shares)	477,272	3,181,818							3,659,090
Additional offering price of common stock (in dollars per share) \| $ / shares	$ 55.00	$ 55.00							$ 55.00
Net proceeds from initial public offering \| $	$ 24,700	$ 163,700							$ 188,400

Stock-Based Awards - Additional Information (Details)			12 Months Ended
Stock-Based Awards - Additional Information (Details)	Jan. 01, 2020 shares	Sep. 21, 2017 shares	Dec. 31, 2019 USD ($) offering_period $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of offering periods \| offering_period			0
Intrinsic value of stock options exercised \| $			$ 53,200,000	$ 4,400,000
Exercised (in shares)			1,504,583		0
Weighted average grant-date fair value per share of options granted (in dollars per share) \| $ / shares			$ 19.22	$ 19.68	$ 7.63
Unrecognized compensation cost related to unvested share-based awards \| $			$ 60,800,000
Unrecognized compensation cost related to unvested share-based awards, period for recognition			2 years 8 months 12 days
Expenses incurred \| $			$ 20,410,000	$ 9,688,000	$ 4,866,000
President And Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense \| $			$ 2,400,000
Time-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units, granted (in shares)			87,000
Weighted average grant date fair value, granted (in dollars per share) \| $ / shares			$ 29.03
Fair-value of units \| $			$ 500,000
Vested (in shares)			12,500	0	0
Forfeited (in shares)			0
Expenses incurred \| $			$ 1,082,000	$ 110,000	$ 0
Time-based restricted stock units \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation, vesting period			4 years	4 years
Time-based restricted stock units \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation, vesting period			1 year	1 year
Performance-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units, granted (in shares)			57,400
Weighted average grant date fair value, granted (in dollars per share) \| $ / shares			$ 34.43
Vested (in shares)			0	0
Forfeited (in shares)			0
Expenses incurred \| $			$ 0
2015 Equity Incentive Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of fair market value of common stock			100.00%
Expected term (in years)			10 years
2015 Equity Incentive Plan \| Employees and Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation, vesting period			4 years
Common Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised (in shares)			1,508,448	140,074
Common Shares \| 2017 Stock Option and Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares reserved for issuance (in shares)		2,655,831	994,282
Effective date from which automatic annual increase in number of shares reserved for future issuance		Jan. 01, 2018
Percentage of automatic annual increase in number of shares reserved for future issuance		4.00%
Common Shares \| 2017 Stock Option and Incentive Plan \| Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in shares reserved for issuance (in shares)	2,064,706
Common Shares \| 2017 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares reserved for issuance (in shares)		306,750	1,009,433
Effective date from which automatic annual increase in number of shares reserved for future issuance		Jan. 01, 2018
Date until which automatic annual increase in number of shares reserved for future issuance		Jan. 01, 2027
Automatic annual increase in number of shares reserved for future issuance (in shares)		400,000
Common Shares \| 2017 Employee Stock Purchase Plan \| Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in shares reserved for issuance (in shares)	400,000
Common Shares \| 2017 Employee Stock Purchase Plan \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of automatic annual increase in number of shares reserved for future issuance		1.00%

Stock-Based Awards - Summary of Assumptions used to Determine the Fair Value of Options Granted to Employees and Directors (Details) - Common Share Option and Stock Appreciation Right Activity	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.20%	2.80%	1.90%
Expected term (in years)	6 years 2 months 12 days	6 years 1 month 6 days	6 years
Expected volatility	74.50%	73.30%	78.30%
Expected dividend yield	0.00%	0.00%	0.00%

Stock-Based Awards - Summary of Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2017
Number of Shares
Outstanding, beginning balance, number of shares (in shares)	5,787,151
Granted (in shares)	3,067,718
Exercised (in shares)	(1,504,583)	0
Forfeited/Expired (in shares)	(599,347)
Outstanding, ending balance, number of shares (in shares)	6,750,939
Options vested and expected to vest (in shares)	6,750,939
Options exercisable (in shares)	3,052,876
Weighted Average Exercise Price
Outstanding, beginning balance (in dollars per share)	$ 10.92
Granted (in dollars per share)	28.77
Exercised (in dollars per share)	4.49
Forfeited/Expired (in dollars per share)	23.40
Outstanding, ending balance (in dollars per share)	19.36
Options vested and expected to vest (in dollars per share)	19.36
Options exercisable (in dollars per share)	$ 10.62
Additional Disclosures
Outstanding, weighted average remaining contractual term	8 years
Options vested and expected to vest, weighted average remaining contractual term	8 years
Options exercisable, weighted average remaining contractual term	6 years 10 months 24 days
Outstanding, aggregate intrinsic value	$ 289,615
Options vested and expected to vest, aggregate intrinsic value	289,615
Options exercisable, aggregate intrinsic value	$ 157,592

Stock-Based Awards - Summary of RSU Activity (Details) - Time-based restricted stock units - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Number of Shares
Outstanding shares, beginning balance (in shares)	25,000
Granted (in shares)	87,000
Vested (in shares)	(12,500)	0	0
Forfeited (in shares)	0
Outstanding shares, ending balance (in shares)	99,500	25,000
Weighted Average Exercise Price
Weighted average grant date fair value, beginning balance (in dollars per share)	$ 33.43
Weighted average grant date fair value, granted (in dollars per share)	29.03
Weighted average grant date fair value, vested (in dollars per share)	33.43
Weighted average grant date fair value, forfeited (in dollars per share)	0
Weighted average grant date fair value, ending balance (in dollars per share)	$ 29.58	$ 33.43

Stock-Based Awards - Classification of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	$ 20,410	$ 9,688	$ 4,866
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	7,934	4,021	1,320
Selling, general, and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	12,476	5,667	3,546
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	19,328	9,578	4,866
Time-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	$ 1,082	$ 110	$ 0

401(k) Savings Plan - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan description		Effective January 1, 2018, the Company adopted the 2018 401(k) Plan, a defined contribution plan under Section 401(k) of the Internal Revenue Code, whereby the Company provides matching contributions of 100% of each employee's contribution up to a maximum matching contribution of 3% of the employee's eligible compensation and at a rate of 50% of each employee's contribution in excess of 3% up to a maximum of 5% of the employee's eligible compensation.
Matching contributions to the plan by employer	$ 0.9		$ 0.4	$ 0.1
Up to Three Percent of Compensation
Defined Contribution Plan Disclosure [Line Items]
Percentage of matching contribution to plan		100.00%
Three to Five Percent of Compensation
Defined Contribution Plan Disclosure [Line Items]
Percentage of matching contribution to plan		50.00%
Clinical Reference Laboratory, Inc.
Defined Contribution Plan Disclosure [Line Items]
Percentage of salary for matching contribution per employee				6.00%
Maximum \| First Tier of Matching
Defined Contribution Plan Disclosure [Line Items]
Employee earnings subject to employer match		3.00%
Maximum \| Second Tier of Matching
Defined Contribution Plan Disclosure [Line Items]
Percentage of salary for matching contribution per employee on time-based vesting		5.00%
Maximum \| Clinical Reference Laboratory, Inc.
Defined Contribution Plan Disclosure [Line Items]
Percentage of matching contribution to plan				50.00%
Minimum \| Second Tier of Matching
Defined Contribution Plan Disclosure [Line Items]
Percentage of salary for matching contribution per employee on time-based vesting		3.00%

Net Loss per Share - Summary of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net loss									$ (192,256)	$ (99,854)	$ (50,284)
Denominator:
Weighted average common shares outstanding—basic and diluted (in shares)									42,869,058	35,390,480	16,792,179
Net loss per share—basic and diluted (in dollars per share)	$ (1.31)	$ (1.28)	$ (0.56)	$ (1.25)	$ (0.86)	$ (0.65)	$ (0.65)	$ (0.66)	$ (4.48)	$ (2.82)	$ (2.99)

Net Loss per Share - Additional Information (Details) - shares	Dec. 31, 2019	Dec. 31, 2018	Oct. 02, 2017
Earnings Per Share [Line Items]
Common stock, shares outstanding (in shares)	51,617,639	37,676,760
No Par Value Common Stock
Earnings Per Share [Line Items]
Common stock, shares outstanding (in shares)			0

Net Loss per Share - Summary of Potential Dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share (in shares)	6,907,839	5,812,151	4,598,352
Unvested time-based restricted common stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share (in shares)	99,500	25,000	0
Unvested performance-based restricted common stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share (in shares)	57,400	0	0
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share (in shares)	6,750,939	5,787,151	4,598,352

Income Taxes - Additional Information (Details) - USD ($)			3 Months Ended	12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Income tax benefits			$ 0	$ 0	$ 0
Federal statutory income tax rate	21.00%	35.00%		21.00%	21.00%	34.00%
Percentage of net operating loss carry forward deductible from current year taxable income					80.00%
Research and orphan drug credit carryforwards				$ 25,267,000	$ 13,457,000
Unrecognized tax benefits				$ 0
Income tax examination, description				There are currently no pending income tax examinations. The Company's tax years that are open under statute are from October 2, 2017 to the present.
Accrued interest or penalties related to uncertain tax positions				$ 0	0
Interest Expense
Income Tax Disclosure [Line Items]
Accrued interest or penalties related to uncertain tax positions				0	$ 0
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards				324,200,000
Net operating loss carryforwards, subject to expiration				$ 14,500,000
Tax credit carryforwards expiration year				2037
Net operating loss carryforwards, carried forward indefinitely				$ 309,700,000
Research and orphan drug credit carryforwards				23,100,000
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards				$ 288,600,000
Tax credit carryforwards expiration year				2032	2032
Net operating loss carryforwards expiration year				2037
Research and orphan drug credit carryforwards				$ 2,800,000

Income Taxes - Reconciliation of U.S. Federal Statutory Income Tax Rate to Effective Income Tax Rate (Details)			12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%	35.00%	21.00%	21.00%	34.00%
State taxes, net of federal benefit			7.00%	6.10%	1.60%
Research and orphan drug credit			5.40%	9.60%	7.70%
Research and orphan drug credit addback			0.00%	0.00%	(6.60%)
Impact of change in tax status			0.00%	0.00%	(8.70%)
Effect of federal tax law change			0.00%	0.00%	(6.10%)
Permanent adjustments and other			3.80%	0.70%	(0.30%)
Increase in deferred tax asset valuation allowance			(37.20%)	(37.40%)	(21.60%)
Effective income tax rate			0.00%	0.00%	0.00%

Income Taxes - Schedule of Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets (liabilities):
Net operating loss carryforwards	$ 85,632	$ 28,906
Research and orphan drug credit carryforwards	25,267	13,457
Stock-based compensation	5,535	4,681
Accrued expenses	2,951	1,270
Operating lease liabilities	5,841	3,200
Operating lease assets	(5,515)	0
Property and equipment	0	(3,200)
Other	(64)	(123)
Total gross deferred tax assets	119,647	48,191
Valuation allowance	(119,647)	(48,191)	$ (10,835)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Schedule of Changes in Valuation Allowance for Deferred Tax Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Valuation allowance as of beginning of year	$ (48,191)	$ (10,835)
Net increases recorded to income tax provision	(71,456)	(37,356)
Valuation allowance as of end of year	$ (119,647)	$ (48,191)

Commitments and Contingencies - Additional Information (Details) - KBA Grants $ in Millions		12 Months Ended
	Dec. 31, 2013 USD ($) award	Dec. 31, 2019
Other Commitments [Line Items]
Number of awards grants \| award	2
Amount of grants awarded \| $	$ 2.0
Period of time after which would be required to repay		10 years

Selected Quarterly Financial Data (Unaudited) - Schedule of Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statements of Operations Data:
Revenues	$ 0	$ 0	$ 25,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 25,000	$ 0	$ 0
Operating Income (Loss)	(70,373)	(58,353)	(22,975)	(49,025)	(33,830)	(25,889)	(22,429)	(21,951)	(200,726)	(104,099)	(50,935)
Net loss	$ (67,216)	$ (56,196)	$ (21,460)	$ (47,384)	$ (32,299)	$ (24,435)	$ (21,690)	$ (21,430)	$ (192,256)	$ (99,854)	$ (50,284)
Net loss per share—basic and diluted (in dollars per share)	$ (1.31)	$ (1.28)	$ (0.56)	$ (1.25)	$ (0.86)	$ (0.65)	$ (0.65)	$ (0.66)	$ (4.48)	$ (2.82)	$ (2.99)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details