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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2018	Feb. 28, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
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	No
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
Entity Common Stock, Shares Outstanding		38,189,052
Entity Public Float			$ 463.5

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 293,764	$ 196,754
Prepaid expenses and other current assets	7,273	1,428
Total current assets	301,037	198,182
Long-term investment-restricted	1,069
Property and equipment, net	13,453	838
Other assets		75
Total assets	315,559	199,095
Current liabilities:
Accounts payable	8,308	4,395
Accrued expenses and other current liabilities	14,248	9,233
Notes payable to related party	187	187
Total current liabilities	22,743	13,815
Notes payable to related party, net of current portion	1,107	1,294
Lease liability, net of current portion	11,347
Other long-term liabilities	381	13
Total liabilities	35,578	15,122
Commitments and contingencies (Note 11)
Stockholders' equity:
Preferred stock value
Common stock value	377	326
Additional paid-in capital	575,327	379,516
Accumulated deficit	(295,723)	(195,869)
Total stockholders' equity	279,981	183,973
Total liabilities and stockholders' equity	$ 315,559	$ 199,095

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	37,676,760	32,591,686
Common stock, shares outstanding	37,676,760	32,591,686

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue	$ 0	$ 0	$ 0
Operating expenses:
Research and development	82,887	39,514	20,163
General and administrative	21,212	11,421	5,675
Total operating expenses	104,099	50,935	25,838
Loss from operations	(104,099)	(50,935)	(25,838)
Other income (expense):
Interest expense	(84)	(95)	(106)
Interest and other income, net	4,329	746	4
Total other income (expense), net	4,245	651	(102)
Net loss and comprehensive loss	$ (99,854)	$ (50,284)	$ (25,940)
Net loss per share-basic and diluted	$ (2.82)	$ (2.99)	$ (2.23)
Weighted average common shares outstanding-basic and diluted	35,390,480	16,792,179	11,626,287

Consolidated Statements of Convertible Preferred Shares and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Series A, B-1, B-2 and C Convertible Preferred Stock [Member]
Beginning balance at Dec. 31, 2015	$ (115,307)	$ 0	$ 4,338	$ (119,645)
Beginning balance, shares at Dec. 31, 2015		0
Issuance of common stock upon exercise of stock options, shares	0
Share-based compensation expense	$ 1,487		1,487
Net loss	(25,940)			(25,940)
Ending balance at Dec. 31, 2016	(139,760)	$ 0	5,825	(145,585)
Ending balance, shares at Dec. 31, 2016		0
Convertible preferred shares, beginning balance at Dec. 31, 2015					$ 137,368
Convertible preferred shares, beginning balance, shares at Dec. 31, 2015					2,756,345
Issuance of convertible preferred shares, net of issuance costs					$ 55,299
Issuance of convertible preferred shares, shares					876,366
Ending balance, Convertible Preferred Shares at Dec. 31, 2016					$ 192,667
Ending balance, Convertible Preferred Shares, shares at Dec. 31, 2016					3,632,711
Effect of Conversion (Note 1)	244,538	$ 244	244,294
Effect of Conversion (Note 1), shares		24,425,190
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 sold in public offering, net of underwriting discounts, commissions and offering costs, shares		8,166,496
Issuance of common stock upon exercise of stock options, shares	0
Share-based compensation expense	$ 4,866		4,866
Net loss	(50,284)			(50,284)
Ending balance at Dec. 31, 2017	183,973	$ 326	379,516	(195,869)
Ending balance, shares at Dec. 31, 2017		32,591,686
Issuance of convertible preferred shares, net of issuance costs					$ 51,871
Issuance of convertible preferred shares, shares					690,333
Effect of Conversion (Note 1), convertible preferred shares					$ (244,538)
Effect of Conversion (Note 1), shares, Convertible preferred shares, shares					(4,323,044)
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 sold in public offering, net of underwriting discounts, commissions and offering costs, shares		4,945,000
Issuance of common stock upon exercise of stock options	$ 915	$ 1	914
Issuance of common stock upon exercise of stock options, shares	140,074	140,074
Share-based compensation expense	$ 9,688		9,688
Net loss	(99,854)			(99,854)
Ending balance at Dec. 31, 2018	$ 279,981	$ 377	$ 575,327	$ (295,723)
Ending balance, shares at Dec. 31, 2018		37,676,760

Consolidated Statements of Convertible Preferred Shares and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Series A, B-1, B-2 and C Convertible Preferred Stock [Member]
Issuance costs	$ 429	$ 25

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (99,854)	$ (50,284)	$ (25,940)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	9,688	4,866	1,487
Depreciation and amortization expense	317	150	90
Loss on disposal of property and equipment		10	6
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(5,770)	(637)	(185)
Accounts payable	3,991	2,904	(187)
Accrued expenses and other current liabilities	4,477	6,276	1,694
Other assets			(55)
Other long-term liabilities	368	13
Net cash used in operating activities	(86,783)	(36,702)	(23,090)
Cash flows from investing activities:
Purchases of property and equipment	(1,125)	(406)	(223)
Increase in restricted investments	(1,069)
Net cash used in investing activities	(2,194)	(406)	(223)
Cash flows from financing activities:
Proceeds from public offerings, net of underwriting discounts and commissions	185,933	129,112
Proceeds from issuance of convertible preferred shares		52,300	55,324
Repayment of notes payable to related party	(187)	(187)	(198)
Payments of public offering costs	(674)	(4,395)	(104)
Payments of convertible preferred share issuance costs		(429)	(25)
Proceeds from exercise of stock options	915
Net cash provided by financing activities	185,987	176,401	54,997
Net increase in cash and cash equivalents	97,010	139,293	31,684
Cash and cash equivalents at beginning of period	196,754	57,461	25,777
Cash and cash equivalents at end of period	293,764	196,754	57,461
Cash paid for interest	84	95	$ 106
Amounts capitalized under build-to-suit lease transaction	$ 11,885
Conversion of convertible preferred shares into common stock		244,538
Purchases of property and equipment included in accounts payable and accrued expenses		$ 78

Nature of the Business and Basis of Presentation	12 Months Ended
Nature of the Business and Basis of Presentation	Dec. 31, 2018
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Deciphera Pharmaceuticals, Inc. (the “Company”) is a clinical-stage biopharmaceutical company developing new drugs to improve the lives of cancer patients by addressing key mechanisms of drug resistance that limit the rate and durability of response of many cancer therapies. The Company’s targeted, small molecule drug candidates, designed using its proprietary kinase switch control inhibitor platform, inhibit the activation of kinases, an important family of enzymes, that, when mutated or over expressed, are known to be directly involved in the growth and spread of many cancers. The Company is subject to risks and uncertainties common to early-stage 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, 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 clinical testing and regulatory approval prior to commercialization. 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. 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 $99.9 million and $50.3 million for the years ended December 31, 2018 and 2017, respectively. As of December 31, 2018, the Company had an accumulated deficit of $295.7 million. The Company expects to continue to generate operating losses in the foreseeable future. The Company expects that its cash and cash equivalents of $293.8 million as of December 31, 2018 will be sufficient to fund its operating expenses, capital expenditure requirements and debt service payments 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 preclinical activities and clinical trials for its drug candidates in development. 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. These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”).

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. 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 revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, 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.

Cash Equivalents

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

Concentrations of Credit Risk and of Significant Suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company maintains all cash and cash equivalents at one accredited financial institution. 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.

Property and Equipment

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


		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 and amortization are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance are charged to expense as incurred.

Impairment of Long-Lived Assets

Long-lived assets consist of property and equipment. 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 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, 2018, 2017 or 2016.

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 are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). 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. The fair value of the Company’s outstanding notes payable to related party (see Note 6) as of December 31, 2018 and 2017 approximated $1.1 million and $1.2 million, respectively. 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 represents a Level 3 measurement.

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 designing, optimizing and introducing small molecule switch control inhibitors of protein kinases for human clinical trials and the global pharmaceutical marketplace through the use of its proprietary drug discovery technology platform. All of the Company’s tangible assets are held in the United States.

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.

Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. 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 United States. 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 general and administrative expenses.

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. The Company accounts for forfeitures as they occur.

The Company classifies stock-based compensation expense in its 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. There was no difference between net loss and comprehensive loss for each of the periods presented in the accompanying consolidated financial statements.

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, 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 year ended December 31, 2016 or for 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 (see Note 1).

Recently Adopted Accounting Pronouncements

In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), which supersedes existing revenue recognition guidance under GAAP. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The standard defines a five-step process to achieve this principle, and will require companies to use more judgment and make more estimates than under the current guidance. The Company expects that these judgments and estimates will include identifying performance obligations in the customer contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. ASU 2014-09 also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts. In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date, which delays the effective date of ASU 2014-09 such that the standard is effective for public entities for annual periods beginning after December 15, 2017 and for interim periods within those fiscal years. In March 2016, the FASB issued ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (“ASU 2016-08”), which further clarifies the implementation guidance on principal versus agent considerations in ASU 2014-09. In April 2016, the FASB issued ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, clarifying the implementation guidance on identifying performance obligations and licensing. Specifically, the amendments in this update reduce the cost and complexity of identifying promised goods or services and improve the guidance for determining whether promises are separately identifiable. The amendments in this update also provide implementation guidance on determining whether an entity’s promise to grant a license provides a customer with either a right to use the entity’s intellectual property (which is satisfied at a point in time) or a right to access the entity’s intellectual property (which is satisfied over time). In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients (“ASU 2016-12”), which clarifies the objective of the collectability criterion, presentation of taxes collected from customers, non-cash consideration, contract modifications at transition, completed contracts at transition and how guidance in ASU 2014-09 is retrospectively applied. ASU 2016-08, ASU 2016-10 and ASU 2016-12 have the same effective dates and transition requirements as ASU 2014-09. In 2018, the Company adopted these standards using the modified retrospective approach which did not have an impact on the Company’s financial position, results of operations or cash flows as the Company does not currently have any revenue-generating arrangements.

In May 2017, the FASB issued ASU No. 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting (“ASU 2017-09”), which clarifies when to account for a change to the terms or conditions of a share-based payment award as a modification. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award (as equity or liability) changes as a result of the change in terms or conditions. The standard is effective for annual periods beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted. The adoption of ASU 2017-09 did not have an impact on the Company’s financial position, results of operations or cash flows.

Recently Issued Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”). ASU 2016-02 will require lessees to recognize most leases on their balance sheet as a right-of-use asset and a lease liability. Leases will be classified as either operating or finance, and classification will be 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. ASU 2016-02 initially required adoption using a modified retrospective approach, under which all years presented in the financial statements would be prepared under the revised guidance. In July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842), which added an optional transition method under which financial statements may be prepared under the revised guidance for the year of adoption, but not for prior years. Under the latter method, entities will recognize a cumulative catch-up adjustment to the opening balance of retained earnings in the period of adoption. The Company intends to adopt the new leasing standards on the effective date of January 1, 2019 using a modified retrospective approach. The Company expects to elect 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 expects that the adoption of the new leasing standards will result in the recognition of material right-of-use assets and lease liabilities and the reversal of the build to suit asset and liabilities on the consolidated balance sheets but does not expect it to have a material impact on its results of operations or cash flows.

In June 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 does not expect that the adoption of ASU 2018-07 will have a material impact on its financial position, results of operations or cash flows.

Fair Value of Financial Assets

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets

3. Fair Value of Financial Assets

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 (in thousands):


	Fair Value Measurements at December 31, 2018 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	267,145	$	—	$	267,145

Total	$	—	$	267,145	$	—	$	267,145


	Fair Value Measurements at December 31, 2017 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	191,950	$	—	$	191,950

Total	$	—	$	191,950	$	—	$	191,950

The table above as of December 31, 2018 excludes a certificate of deposit of $1.1 million that the Company held to secure a letter of credit associated with a lease (see Note 11).

During the years ended December 31, 2018 and 2017, there were no transfers between Level 1, Level 2 and Level 3.

- 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, 2018

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

4. Property and Equipment, Net

Property and equipment, net consisted of the following (in thousands):


	December 31,
	2018			2017
Laboratory equipment	$	1,731		$	981
Computer equipment		465			300
Leasehold improvements		359			344
Furniture and fixtures		201			128
Construction in progress (Note 11)		11,914			—

		14,670			1,753
Less: Accumulated depreciation and amortization		(1,217	)		(915	)

	$	13,453		$	838

Depreciation and amortization expense was $0.3 million, $0.2 million and $0.1 million for the years ended December 31, 2018, 2017 and 2016, respectively.

Accrued Expenses

12 Months Ended

Dec. 31, 2018

Payables and Accruals [Abstract]

Accrued Expenses

5. Accrued Expenses

Accrued expenses consisted of the following (in thousands):


	December 31,
	2018		2017
Accrued external research and development expenses	$	8,761	$	6,625
Accrued payroll and related expenses		4,139		2,233
Accrued professional fees		747		353
Accrued other		601		22

	$	14,248	$	9,233

Notes Payable to Related Party

12 Months Ended

Dec. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Notes Payable to Related Party

6. Notes Payable to Related Party

In June 2010, the Company entered into a loan agreement and a security agreement (together, the “CRL Construction Loan”) with Clinical Reference Laboratory, Inc. (“CRL”), a related party (see Note 14), which provided for aggregate borrowings of up to $2.8 million to finance construction of the Company’s biology and chemistry laboratories. Borrowings under the CRL Construction Loan bear interest at a fixed rate equal to 6.0% per annum and interest accrues monthly. The CRL Construction Loan requires monthly payments of principal and interest commencing on January 1, 2011 and through the maturity date of January 1, 2026, based on a 15-year straight-line amortization schedule.

The CRL Construction Loan is 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 has agreed to affirmative, negative and financial covenants to which it will remain subject until the loan has been paid off in full. These covenants include 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 include 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 include the ability to accelerate all amounts that are due under the CRL Construction Loan to become immediately due and payable. As of December 31, 2018 and 2017, the Company was in compliance with the financial covenants of the CRL Construction Loan.

Notes payable to related party as of December 31, 2018 and 2017 consisted only of outstanding borrowings under the CRL Construction Loan, as follows (in thousands):


	December 31,
	2018			2017
Notes payable to related party	$	1,294		$	1,481
Less: Current portion		(187	)		(187	)

Notes payable to related party, net of current portion	$	1,107		$	1,294

As of December 31, 2018, scheduled payments of principal and interest for the CRL Construction Loan are as follows (in thousands):


Year ending December 31,	Principal		Interest		Total
2019		187		73		260
2020		187		61		248
2021		187		50		237
2022		187		39		226
2023		187		28		215
Thereafter		359		21		380

	$	1,294	$	272	$	1,566

Total interest expense for each of the years ended December 31, 2018, 2017 and 2016 was $0.1 million.

Convertible Preferred Shares	12 Months Ended
Convertible Preferred Shares	Dec. 31, 2018
Text Block [Abstract]
Convertible Preferred Shares	7. Convertible Preferred Shares Prior to the completion of its IPO in October 2017 (Note 1), the Company had outstanding Series A, Series B-1, Series B-2 and Series C convertible preferred shares. The Conversion (Note 1) 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. 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. In July 2016, the Company issued and sold 876,366 Series B-2 Shares at a price of $63.13 per share for gross proceeds of $55.3 million. Issuance costs associated with the issuance of Series B-2 Shares were less than $0.1 million.

Common Stock	12 Months Ended
Common Stock	Dec. 31, 2018
Equity Abstract
Common Stock	8. 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.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Compensation

9. Stock-Based Compensation

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, 2018, 2,099,983 remained available for issuance under the 2017 Plan. The number of shares reserved for issuance under the 2017 Plan was increased by 1,507,070 shares effective January 1, 2019.

2015 Equity Incentive Plan

Under the Company’s 2015 Equity Incentive Plan (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, 2018, 632,666 remained available for issuance under the ESPP Plan. The number of shares reserved for issuance under the ESPP was increased by 376,767 shares effective January 1, 2019.

As of December 31, 2018, 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,
	2018			2017			2016
Risk-free interest rate		2.8	%		1.9	%		1.3	%
Expected term (in years)		6.1			6.0			6.1
Expected volatility		73.3	%		78.3	%		76.1	%
Expected dividend yield		0	%		0	%		0	%

The following table summarizes the Company’s option activity from January 1, 2018 to December 31, 2018:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)		(in thousands)
Outstanding as of December 31, 2017		4,598,352		$	4.99
Granted		1,472,600		$	29.64
Exercised		(140,074	)	$	6.54
Forfeited		(143,727	)	$	17.09

Outstanding as of December 31, 2018		5,787,151		$	10.92		7.7	$	70,479

Options vested and expected to vest as of December 31, 2018		5,787,151		$	10.92		7.7	$	70,479

Options exercisable as of December 31, 2018		3,312,447		$	5.20		6.8	$	53,742

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 year ended December 31, 2018 was $4.4 million. There were no option exercises during the years ended December 31, 2017 and 2016.

The weighted average grant-date fair value per share of options granted during the years ended December 31, 2018, 2017 and 2016 was $19.68, $7.63 and $2.43, respectively.

Restricted Stock Units

The 2017 Plan provides for the award of restricted stock units. During 2018, the Company granted restricted stock units to employees that were subject to time-based vesting conditions that lapse over two years from date of grant. 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 vesting conditions are valued on the grant date using the grant date market price of the underlying shares. The Company did not grant restricted stock units in 2017 or 2016.

The table below summarizes the Company’s restricted stock unit activity from January 1, 2018 to December 31, 2018:


	Number of Shares		Weighted Average Grant Date Fair Value
Outstanding as of December 31, 2017		—	$	—
Granted		25,000	$	33.43
Vested		—	$	—
Forfeited		—	$	—

Outstanding as of December 31, 2018		25,000	$	33.43

Stock-Based Compensation

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


	Year Ended December 31,
	2018		2017		2016
Research and development expenses	$	4,021	$	1,320	$	541
General and administrative expenses		5,667		3,546		946

	$	9,688	$	4,866	$	1,487

As of December 31, 2018, total unrecognized compensation cost related to the unvested share-based awards was $27.2 million, which is expected to be recognized over a weighted average of 2.2 years.

Net Loss per Share

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Net Loss per Share

10. Net Loss per Share

Basic and diluted net loss per share was calculated as follows (in thousands, except share and per share amounts):


	Year Ended December 31,
	2018			2017			2016
Numerator:
Net loss	$	(99,854	)	$	(50,284	)	$	(25,940	)

Denominator:
Weighted average common shares outstanding—basic and diluted		35,390,480			16,792,179			11,626,287


Net loss per share—basic and diluted	$	(2.82	)	$	(2.99	)	$	(2.23	)

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 (see Note 1). 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 year ended December 31, 2016 or 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 those periods, 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,
	2018		2017		2016
Options to purchase common stock		5,787,151		4,598,352		3,214,452
Unvested restricted common stock units		25,000		—		—
Series B convertible preferred shares (as converted to common shares)		—		—		8,898,527

		5,812,151		4,598,352		12,112,979

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

11. Commitments and Contingencies

Leases

The Company has a three-year sublease agreement for office space in Waltham, Massachusetts that began in September 2016 and expires in September 2019. In addition, in August 2018, the Company entered into a nine-month sublease for additional office space in Waltham, Massachusetts that expires in May 2019.

The Company has 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.

Payment escalations specified in the lease agreements are accrued, and rent expense is recognized on a straight-line basis over the terms of occupancy.

The Company recorded rent expense of $1.1 million, $0.6 million and $0.4 million during the years ended December 31, 2018, 2017 and 2016, respectively.

The following table summarizes the future minimum lease payments due under the operating leases as of December 31, 2018 (in thousands):


Year Ending December 31,
2019	$	726
2020		333

	$	1,059

Build-to-suit lease

In May 2018, the Company entered into a lease for office space in Waltham, Massachusetts. The lease term is expected to commence on May 1, 2019 and expires 10 years and 7 months from the commencement date, 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. 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 certificate of deposit 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, 2018. The lease agreement allows for a landlord-provided tenant improvement allowance of $2.7 million to be applied to the costs of the construction of the leasehold improvements.

The Company is not the legal owner of the leased space. However, in accordance with ASC 840, Leases, the Company is deemed to be the owner of the 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 and recorded a corresponding build-to-suit facility lease financing obligation. As of December 31, 2018, the current portion of the lease financing obligation of $0.5 million was classified within accrued expenses and other current liabilities and the remaining $11.4 million was classified as a long-term lease liability, net of current portion, on its consolidated balance sheet. The construction is expected to be completed in the second quarter of 2019.

As of December 31, 2018, minimum commitments under this lease are as follows (in thousands):


Year Ending December 31,
2019	$	170
2020		2,043
2021		2,088
2022		2,132
2023		2,177
Thereafter		13,783

	$	22,393

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. 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.

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, 2018 or 2017.

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

12. 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 year ended December 31, 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,
	2018			2017
Federal statutory income tax rate		21.0	%		34.0	%
State taxes, net of federal benefit		6.1			1.6
Research and orphan drug credit		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		0.7			(0.3	)
Increase in deferred tax asset valuation allowance		(37.4	)		(21.6	)

Effective income tax rate		—	%		—	%

Net deferred tax assets consisted of the following (in thousands):


	December 31,
	2018			2017
Deferred tax assets (liabilities):
Net operating loss carryforwards	$	28,906		$	4,030
Research and orphan drug credit carryforwards		13,457			3,888
Stock-based compensation		4,681			2,366
Accrued expenses and lease liability		4,470			672
Property and equipment		(3,200	)		(129	)
Other		(123	)		8

Total gross deferred tax assets		48,191			10,835
Valuation allowance		(48,191	)		(10,835	)

Net deferred tax assets	$	—		$	—

On December 22, 2017, the Tax Cuts and Jobs Act (the “TCJA”) was signed into United States 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, 2017 (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 related to the re-measurement of the Company’s deferred tax balance was a reduction of $3.1 million for the year ended December 31, 2017. 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.

Upon the Conversion in October 2017, the Company became subject to U.S. federal and state income taxes. The change in the valuation allowance was as follows (in thousands):


	Year Ended December 31,
	2018			2017
Valuation allowance as of beginning of year	$	(10,835	)	$	—
Net increases recorded to income tax provision		(37,356	)		(10,835	)

Valuation allowance as of end of year	$	(48,191	)	$	(10,835	)

As of December 31, 2018, the Company had net operating loss carryforwards for federal income tax purposes of $107.1 million, of which $14.5 million begin to expire in 2037 and $92.6 million may be carried forward indefinitely. As of December 31, 2018, the Company had net operating loss carryforwards for state income tax purposes of $107.7 million, which begin to expire in 2027. As of December 31, 2018, the Company also had available research and orphan drug credit carryforwards for federal and state income tax purposes of $12.8 million and $0.9 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, 2018. 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, 2018.

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.

401(k) Savings Plan	12 Months Ended
401(k) Savings Plan	Dec. 31, 2018
Retirement Benefits [Abstract]
401(k) Savings Plan	13. 401(k) Savings Plan Effective January 1, 2018, the Company adopted the Deciphera Pharmaceuticals 401(k) Plan (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 CRL, a related party (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 $0.4 million, $0.1 million and less than $0.1 million respectively, for the years ended December 31, 2018, 2017 and 2016.

Related Parties	12 Months Ended
Related Parties	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Parties	14. Related Parties *Clinical Reference Laboratory, Inc.* One of the members of the Company’s board of directors is the Chief Executive Officer of CRL. CRL is the owner of approximately 31% of Brightstar, a holder of more than 5% of the Company’s common stock. The Company is a party to a loan agreement and a security agreement, each dated as of June 11, 2010, with CRL. 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 2016, the loan was assigned to CHC, Inc., a related party, which owns 100% of CRL. Borrowings under the loan bear interest at a fixed rate equal to 6.0% per annum and the Company is required to make monthly payments of principal and interest, based on a 15-year straight-line amortization schedule. For each of the years ended December 31, 2018, 2017 and 2016, the Company recorded $0.1 million of interest expense related to this loan. For each of the years ended December 31, 2018, 2017 and 2016, the Company made $0.3 million in principal and interest payments under the loan. As of December 31, 2018 and 2017, principal amounts owed under the loan agreement totaled $1.3 million and $1.5 million, respectively (see Note 6). The Company is party to a master services agreement, effective as of May 20, 2013, with CRL under which the Company purchased and expects to continue to purchase laboratory services. Under the agreement, the Company has agreed to use CRL on an exclusive basis for laboratory testing needs. For the years ended December 31, 2018, 2017 and 2016, the Company recorded $0.9 million, $0.4 million and $0.2 million, respectively, of research and development expense incurred under this agreement, of which $0.8 million, $0.4 million and $0.1 million, respectively, was paid to CRL during those same periods. As of December 31, 2018 and 2017, total amounts owed to CRL for laboratory services were $0.2 million and $0.1 million, respectively, which amounts were included in accounts payable and accrued expenses. The Company is not committed to purchase any minimum amounts under the agreement. In 2015, the Company entered into an agreement with CRL under which the Company became a participating employer in CRL’s 401(k) plan. Effective January 1, 2018, the Company adopted the 2018 401(k) Plan to which employees’ and former employees’ accounts were transitioned from the CRL 401(k) Plan. For the year ended December 31, 2018, no contributions were made by employees of the Company to the CRL 401(k) Plan. For the years ended December 31, 2017 and 2016, the total amount of contributions made by employees of the Company under the CRL 401(k) Plan was $0.6 million and $0.2 million, respectively.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

15. 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 (in thousands except per share data):


	Three Months Ended
	Dec. 31, 2018			Sept. 30, 2018			June 30, 2018			March 31, 2018			Dec. 31, 2017			Sept. 30, 2017			June 30, 2017			March 31, 2017
Statements of Operations Data:
Revenue	$	—		$	—		$	—		$	—		$	—		$	—		$	—		$	—
Loss from operations		(33,830	)		(25,889	)		(22,429	)		(21,951	)		(20,338	)		(12,181	)		(10,691	)		(7,725	)
Net loss		(32,299	)		(24,435	)		(21,690	)		(21,430	)		(19,912	)		(12,038	)		(10,626	)		(7,708	)
Net loss per share—basic and diluted		(0.86	)		(0.65	)		(0.65	)		(0.66	)		(0.62	)		(1.04	)		(0.91	)		(0.66	)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Use of Estimates

Use of Estimates

Cash Equivalents

Cash Equivalents

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

Concentrations of Credit Risk and of Significant Suppliers

Concentrations of Credit Risk and of Significant Suppliers

Property and Equipment

Property and Equipment


		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

Impairment of Long-Lived Assets

Fair Value Measurements

Fair Value Measurements

•

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

•

Segment Information

Segment Information

Research and Development Costs

Research and Development Costs

Research Contract Costs and Accruals

Research Contract Costs and Accruals

Patent Costs

Patent Costs

Stock-Based Compensation

Stock-Based Compensation

Income Taxes

Income Taxes

Comprehensive Loss

Comprehensive Loss

Net Loss per Share

Net Loss per Share

Recently Adopted and Recently Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements

Recently Issued Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Summary of Estimated Useful life of Assets

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


		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

Fair Value of Financial Assets (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

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


	Fair Value Measurements at December 31, 2018 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	267,145	$	—	$	267,145

Total	$	—	$	267,145	$	—	$	267,145


	Fair Value Measurements at December 31, 2017 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	191,950	$	—	$	191,950

Total	$	—	$	191,950	$	—	$	191,950

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Summary of Property and Equipment, Net

Property and equipment, net consisted of the following (in thousands):


	December 31,
	2018			2017
Laboratory equipment	$	1,731		$	981
Computer equipment		465			300
Leasehold improvements		359			344
Furniture and fixtures		201			128
Construction in progress (Note 11)		11,914			—

		14,670			1,753
Less: Accumulated depreciation and amortization		(1,217	)		(915	)

	$	13,453		$	838

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2018

Payables and Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consisted of the following (in thousands):


	December 31,
	2018		2017
Accrued external research and development expenses	$	8,761	$	6,625
Accrued payroll and related expenses		4,139		2,233
Accrued professional fees		747		353
Accrued other		601		22

	$	14,248	$	9,233

Notes Payable to Related Party (Tables)

12 Months Ended

Dec. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Notes Payable to Related Party

Notes payable to related party as of December 31, 2018 and 2017 consisted only of outstanding borrowings under the CRL Construction Loan, as follows (in thousands):


	December 31,
	2018			2017
Notes payable to related party	$	1,294		$	1,481
Less: Current portion		(187	)		(187	)

Notes payable to related party, net of current portion	$	1,107		$	1,294

Schedules Payments of Principal and Interest

As of December 31, 2018, scheduled payments of principal and interest for the CRL Construction Loan are as follows (in thousands):


Year ending December 31,	Principal		Interest		Total
2019		187		73		260
2020		187		61		248
2021		187		50		237
2022		187		39		226
2023		187		28		215
Thereafter		359		21		380

	$	1,294	$	272	$	1,566

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

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


	Year Ended December 31,
	2018			2017			2016
Risk-free interest rate		2.8	%		1.9	%		1.3	%
Expected term (in years)		6.1			6.0			6.1
Expected volatility		73.3	%		78.3	%		76.1	%
Expected dividend yield		0	%		0	%		0	%

Summary of Option Activity

The following table summarizes the Company’s option activity from January 1, 2018 to December 31, 2018:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)		(in thousands)
Outstanding as of December 31, 2017		4,598,352		$	4.99
Granted		1,472,600		$	29.64
Exercised		(140,074	)	$	6.54
Forfeited		(143,727	)	$	17.09

Outstanding as of December 31, 2018		5,787,151		$	10.92		7.7	$	70,479

Options vested and expected to vest as of December 31, 2018		5,787,151		$	10.92		7.7	$	70,479

Options exercisable as of December 31, 2018		3,312,447		$	5.20		6.8	$	53,742

Summary of RSU Activity

The table below summarizes the Company’s restricted stock unit activity from January 1, 2018 to December 31, 2018:


	Number of Shares		Weighted Average Grant Date Fair Value
Outstanding as of December 31, 2017		—	$	—
Granted		25,000	$	33.43
Vested		—	$	—
Forfeited		—	$	—

Outstanding as of December 31, 2018		25,000	$	33.43

Classification of Stock-Based Compensation Expense

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


	Year Ended December 31,
	2018		2017		2016
Research and development expenses	$	4,021	$	1,320	$	541
General and administrative expenses		5,667		3,546		946

	$	9,688	$	4,866	$	1,487

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Summary of Basic and Diluted Net Loss per Share

Basic and diluted net loss per share was calculated as follows (in thousands, except share and per share amounts):


	Year Ended December 31,
	2018			2017			2016
Numerator:
Net loss	$	(99,854	)	$	(50,284	)	$	(25,940	)

Denominator:
Weighted average common shares outstanding—basic and diluted		35,390,480			16,792,179			11,626,287


Net loss per share—basic and diluted	$	(2.82	)	$	(2.99	)	$	(2.23	)

Summary of Potential Dilutive Securities


	As of December 31,
	2018		2017		2016
Options to purchase common stock		5,787,151		4,598,352		3,214,452
Unvested restricted common stock units		25,000		—		—
Series B convertible preferred shares (as converted to common shares)		—		—		8,898,527

		5,812,151		4,598,352		12,112,979

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Summary of Future Minimum Lease Payments under Operating Leases

The following table summarizes the future minimum lease payments due under the operating leases as of December 31, 2018 (in thousands):


Year Ending December 31,
2019	$	726
2020		333

	$	1,059

Summary of Future Minimum Lease Payments

As of December 31, 2018, minimum commitments under this lease are as follows (in thousands):


Year Ending December 31,
2019	$	170
2020		2,043
2021		2,088
2022		2,132
2023		2,177
Thereafter		13,783

	$	22,393

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

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,
	2018			2017
Federal statutory income tax rate		21.0	%		34.0	%
State taxes, net of federal benefit		6.1			1.6
Research and orphan drug credit		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		0.7			(0.3	)
Increase in deferred tax asset valuation allowance		(37.4	)		(21.6	)

Effective income tax rate		—	%		—	%

Schedule of Net Deferred Tax Assets

Net deferred tax assets consisted of the following (in thousands):


	December 31,
	2018			2017
Deferred tax assets (liabilities):
Net operating loss carryforwards	$	28,906		$	4,030
Research and orphan drug credit carryforwards		13,457			3,888
Stock-based compensation		4,681			2,366
Accrued expenses and lease liability		4,470			672
Property and equipment		(3,200	)		(129	)
Other		(123	)		8

Total gross deferred tax assets		48,191			10,835
Valuation allowance		(48,191	)		(10,835	)

Net deferred tax assets	$	—		$	—

Schedule of Changes in Valuation Allowance for Deferred Tax Assets

The change in the valuation allowance was as follows (in thousands):


	Year Ended December 31,
	2018			2017
Valuation allowance as of beginning of year	$	(10,835	)	$	—
Net increases recorded to income tax provision		(37,356	)		(10,835	)

Valuation allowance as of end of year	$	(48,191	)	$	(10,835	)

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Schedule of Selected Quarterly Financial Data


	Three Months Ended
	Dec. 31, 2018			Sept. 30, 2018			June 30, 2018			March 31, 2018			Dec. 31, 2017			Sept. 30, 2017			June 30, 2017			March 31, 2017
Statements of Operations Data:
Revenue	$	—		$	—		$	—		$	—		$	—		$	—		$	—		$	—
Loss from operations		(33,830	)		(25,889	)		(22,429	)		(21,951	)		(20,338	)		(12,181	)		(10,691	)		(7,725	)
Net loss		(32,299	)		(24,435	)		(21,690	)		(21,430	)		(19,912	)		(12,038	)		(10,626	)		(7,708	)
Net loss per share—basic and diluted		(0.86	)		(0.65	)		(0.65	)		(0.66	)		(0.62	)		(1.04	)		(0.91	)		(0.66	)

Nature of the Business and Basis of Presentation - Additional Information (Detail) $ / shares in Units, $ in Thousands				1 Months Ended		3 Months Ended								12 Months Ended
	Jun. 20, 2018 USD ($) $ / shares shares	Jun. 11, 2018 USD ($) $ / shares shares	Oct. 02, 2017 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	Oct. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Nature Of Business And Basis Of Presentation [Line Items]
Share conversion ratio			5.65
Accumulated deficit						$ (295,723)				$ (195,869)				$ (295,723)	$ (195,869)
Cash and cash equivalents						293,764				196,754				293,764	196,754	$ 57,461	$ 25,777
Net loss						$ (32,299)	$ (24,435)	$ (21,690)	$ (21,430)	$ (19,912)	$ (12,038)	$ (10,626)	$ (7,708)	$ (99,854)	$ (50,284)	$ (25,940)
Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Number of shares issued and sold \| shares														4,945,000	8,166,496
Net proceeds from initial public offering	$ 24,300	$ 161,000		$ 185,300
IPO [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Number of shares issued and sold \| shares			7,500,000		8,166,496
Additional offering price of common stock \| $ / shares			$ 17.00		$ 17.00
Net proceeds from initial public offering			$ 114,100		$ 124,600
IPO [Member] \| Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Number of shares issued and sold \| shares	645,000	4,300,000		4,945,000
Additional offering price of common stock \| $ / shares	$ 40.00	$ 40.00		$ 40.00				$ 40.00

Summary of Significant Accounting Policies - Summary of Estimated Useful life of Assets (Detail)	12 Months Ended
	Dec. 31, 2018
Lab Equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful lives	5 years
Lab Equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful lives	7 years
Computer Equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful lives	3 years
Computer Equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful lives	5 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful lives	7 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful lives	Shorter of life of lease or 15 years

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Significant Accounting Policies [Line Items]
Method of depreciation and amortization expense calculation	Straight-line method
Impairment losses on long-lived assets	$ 0	$ 0	$ 0
Common stock, shares outstanding	37,676,760	32,591,686
No Par Value Common Stock [Member]
Significant Accounting Policies [Line Items]
Common stock, shares outstanding	0	0	0
CRL Construction Loan [Member]
Significant Accounting Policies [Line Items]
Fair value of outstanding notes payable to related party	$ 1,100,000	$ 1,200,000
Minimum [Member]
Significant Accounting Policies [Line Items]
Income tax examination, likelihood percentage	50

Fair Value of Financial Assets - Schedule of Financial Assets Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Cash equivalents:
Total Cash equivalents	$ 267,145	$ 191,950
Money Market Funds [Member]
Cash equivalents:
Total Cash equivalents	267,145	191,950
Level 2 [Member]
Cash equivalents:
Total Cash equivalents	267,145	191,950
Level 2 [Member] \| Money Market Funds [Member]
Cash equivalents:
Total Cash equivalents	$ 267,145	$ 191,950

Fair Value of Financial Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value of Assets and Liabilities Measured on Non Recurring Basis [Line Items]
Transfers between Level 1, Level 2 and Level 3	$ 0	$ 0
Certificates of Deposit [Member] \| Letter of Credit [Member]
Fair Value of Assets and Liabilities Measured on Non Recurring Basis [Line Items]
Cash balance held to secure letter of credit associated with lease	$ 1,100,000

Property and Equipment, Net - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 14,670	$ 1,753
Less: Accumulated depreciation and amortization	(1,217)	(915)
Property and equipment, net	13,453	838
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,731	981
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	465	300
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	359	344
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	201	$ 128
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 11,914

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 317	$ 150	$ 90

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts Payable and Accrued Liabilities [Abstract]
Accrued external research and development expenses	$ 8,761	$ 6,625
Accrued payroll and related expenses	4,139	2,233
Accrued professional fees	747	353
Accrued other	601	22
Accrued Expenses	$ 14,248	$ 9,233

Notes Payable to Related Parties - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2010
Clinical Reference Laboratory, Inc. [Member] \| Loan and Security Agreement [Member]
Related Party Transaction [Line Items]
Aggregate borrowings	$ 2.8			$ 2.8
Fixed interest rate				6.00%
Debt instrument payment term		15-year straight-line amortization schedule.
CRL Construction Loan [Member]
Related Party Transaction [Line Items]
Total interest expense	$ 0.1	$ 0.1	$ 0.1

Notes Payable to Related Party - Schedule of Notes Payable to Related Party (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Less: Current portion	$ (187)	$ (187)
Notes payable to related party, net of current portion	1,107	1,294
CRL Construction Loan [Member]
Related Party Transaction [Line Items]
Notes payable to related party	1,294	1,481
Less: Current portion	(187)	(187)
Notes payable to related party, net of current portion	$ 1,107	$ 1,294

Notes Payable to Related Parties - Schedules Payments of Principal and Interest (Detail) - CRL Construction Loan [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Principal	$ 1,294	$ 1,481
Interest	272
Total	1,566
2019 [Member]
Related Party Transaction [Line Items]
Principal	187
Interest	73
Total	260
2020 [Member]
Related Party Transaction [Line Items]
Principal	187
Interest	61
Total	248
2021 [Member]
Related Party Transaction [Line Items]
Principal	187
Interest	50
Total	237
2022 [Member]
Related Party Transaction [Line Items]
Principal	187
Interest	39
Total	226
2023 [Member]
Related Party Transaction [Line Items]
Principal	187
Interest	28
Total	215
Thereafter [Member]
Related Party Transaction [Line Items]
Principal	359
Interest	21
Total	$ 380

Convertible Preferred Shares - Additional Information (Detail) - USD ($)		1 Months Ended			12 Months Ended
	Oct. 02, 2017	Oct. 31, 2017	May 31, 2017	Jul. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Redeemable Noncontrolling Interest [Line Items]
Conversion of preferred stock to common stock	24,425,190	24,425,190
Proceeds from issuance of convertible preferred shares					$ 52,300,000	$ 55,324,000
Payments of convertible preferred share issuance costs					$ 429,000	$ 25,000
Series C Convertible Preferred Shares [Member]
Redeemable Noncontrolling Interest [Line Items]
Number of convertible preferred shares sold under share purchase agreement			690,333
Convertible preferred shares sold under share purchase agreement, price per share			$ 75.76
Proceeds from issuance of convertible preferred shares			$ 51,900,000
Payments of convertible preferred share issuance costs			$ 400,000
Series B-2 Convertible Preferred Stock [Member]
Redeemable Noncontrolling Interest [Line Items]
Number of convertible preferred shares sold under share purchase agreement				876,366
Convertible preferred shares sold under share purchase agreement, price per share				$ 63.13
Proceeds from issuance of convertible preferred shares				$ 55,300,000
Series B-2 Convertible Preferred Stock [Member] \| Maximum [Member]
Redeemable Noncontrolling Interest [Line Items]
Payments of convertible preferred share issuance costs				$ 100,000

Common Stock - Additional Information (Detail) $ / shares in Units, $ in Thousands					1 Months Ended		12 Months Ended
	Jun. 20, 2018 USD ($) $ / shares shares	Jun. 11, 2018 USD ($) $ / shares shares	Oct. 04, 2017 USD ($) $ / shares shares	Oct. 02, 2017 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	Oct. 31, 2017 USD ($) $ / shares 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				24,425,190		24,425,190
Proceeds from additional offering of shares \| $							$ 185,933	$ 129,112
Common Stock [Member]
Class of Stock [Line Items]
Number of additional shares issued and sold							4,945,000	8,166,496
Net proceeds from initial public offering \| $	$ 24,300	$ 161,000			$ 185,300
IPO [Member]
Class of Stock [Line Items]
Number of additional shares issued and sold				7,500,000		8,166,496
Additional offering price of common stock \| $ / shares				$ 17.00		$ 17.00
Net proceeds from initial public offering \| $				$ 114,100		$ 124,600
IPO [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Number of additional shares issued and sold	645,000	4,300,000			4,945,000
Additional offering price of common stock \| $ / shares	$ 40.00	$ 40.00			$ 40.00
Over-Allotment Option [Member]
Class of Stock [Line Items]
Number of additional shares issued and sold			666,496
Additional offering price of common stock \| $ / shares			$ 17.00
Proceeds from additional offering of shares \| $			$ 10,500

Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Millions				12 Months Ended
	Jan. 01, 2019 shares	Dec. 31, 2018 USD ($) shares	Sep. 21, 2017 shares	Dec. 31, 2018 USD ($) OfferingPeriods $ / shares shares	Dec. 31, 2017 $ / shares shares	Dec. 31, 2016 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of offering periods \| OfferingPeriods				0
Intrinsic value of stock options exercised \| $				$ 4.4
Number of shares, exercised				140,074	0	0
Weighted average grant-date fair value per share of options granted \| $ / shares				$ 19.68	$ 7.63	$ 2.43
Unrecognized compensation cost related to unvested share-based awards \| $		$ 27.2		$ 27.2
Unrecognized compensation cost related to unvested share-based awards, period for recognition		2 years 2 months 12 days
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation, vesting period				2 years
Restricted stock units, granted				25,000	0	0
2015 Equity Incentive Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of fair market value of common stock				100.00%
2015 Equity Incentive Plan [Member] \| Employees and Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation, vesting period				4 years
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, exercised				140,074
Common Stock [Member] \| 2017 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares reserved for issuance		2,099,983	2,655,831	2,099,983
Percentage of automatic annual increase in number of shares reserved for future issuance			4.00%
Effective date from which automatic annual increase in number of shares reserved for future issuance			Jan. 01, 2018
Common Stock [Member] \| 2017 Stock Option and Incentive Plan [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in shares reserved for issuance	1,507,070
Common Stock [Member] \| 2017 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares reserved for issuance		632,666	306,750	632,666
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			400,000
Common Stock [Member] \| 2017 Employee Stock Purchase Plan [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in shares reserved for issuance	376,767
Common Stock [Member] \| 2017 Employee Stock Purchase Plan [Member] \| Minimum [Member]
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 Compensation - Summary of Assumptions used to Determine the Fair Value of Options Granted to Employees and Directors (Detail) - Common Share Option and Stock Appreciation Right Activity [Member]	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.80%	1.90%	1.30%
Expected term (in years)	6 years 1 month 6 days	6 years	6 years 1 month 6 days
Expected volatility	73.30%	78.30%	76.10%
Expected dividend yield	0.00%	0.00%	0.00%

Stock-Based Compensation - Summary of Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, Beginning Balance, Number of Shares	4,598,352
Granted, Number of Shares	1,472,600
Exercised, Number of Shares	(140,074)	0	0
Forfeited, Number of Shares	(143,727)
Outstanding, Ending Balance, Number of Shares	5,787,151	4,598,352
Options vested and expected to vest, Ending Balance, Number of Shares	5,787,151
Options exercisable, Ending Balance, Number of Shares	3,312,447
Outstanding, Beginning Balance, Weighted Average Exercise Price	$ 4.99
Granted, Weighted Average Exercise Price	29.64
Exercised, Weighted Average Exercise Price	6.54
Forfeited, Weighted Average Exercise Price	17.09
Outstanding, Ending Balance, Weighted Average Exercise Price	10.92	$ 4.99
Options vested and expected to vest, Ending Balance, Weighted Average Exercise Price	10.92
Options exercisable, Ending Balance, Weighted Average Exercise Price	$ 5.20
Outstanding, Beginning Balance, Weighted Average Remaining Contractual Term	7 years 8 months 12 days
Options vested and expected to vest, Ending Balance, Weighted Average Remaining Contractual Term	7 years 8 months 12 days
Options exercisable, Ending Balance, Weighted Average Remaining Contractual Term	6 years 9 months 18 days
Outstanding, Beginning Balance, Aggregate Intrinsic Value	$ 70,479
Options vested and expected to vest, Ending Balance, Aggregate Intrinsic Value	70,479
Options exercisable, Ending Balance, Aggregate Intrinsic Value	$ 53,742

Stock-Based Compensation - Summary of RSU Activity (Detail) - Restricted Stock Units (RSUs) [Member] - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	25,000	0	0
Vested	0
Forfeited	0
Outstanding shares, ending balance	25,000
Weighted average grant date fair value, granted	$ 33.43
Weighted average grant date fair value, vested	0
Weighted average grant date fair value, forfeited	0
Weighted average grant date fair value, ending balance	$ 33.43

Stock-Based Compensation - Classification of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 9,688	$ 4,866	$ 1,487
Research and Development Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	4,021	1,320	541
General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 5,667	$ 3,546	$ 946

Net Loss per Share - Summary of Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net loss									$ (99,854)	$ (50,284)	$ (25,940)
Denominator:
Weighted average common shares outstanding-basic and diluted									35,390,480	16,792,179	11,626,287
Net loss per share-basic and diluted	$ (0.86)	$ (0.65)	$ (0.65)	$ (0.66)	$ (0.62)	$ (1.04)	$ (0.91)	$ (0.66)	$ (2.82)	$ (2.99)	$ (2.23)

Net Loss per Share - Additional Information (Detail) - shares	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Line Items]
Common stock, shares outstanding	37,676,760	32,591,686
No Par Value Common Stock [Member]
Earnings Per Share [Line Items]
Common stock, shares outstanding	0	0	0

Net Loss per Share - Summary of Potential Dilutive Securities (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share	5,812,151	4,598,352	12,112,979
Series B Convertible Preferred Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share			8,898,527
Unvested Restricted Common Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share	25,000
Options to Purchase Common Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share	5,787,151	4,598,352	3,214,452

Commitments and Contingencies - Additional Information (Detail) $ in Thousands		1 Months Ended	12 Months Ended
	Dec. 31, 2013 USD ($) award	Aug. 30, 2018	Dec. 31, 2018 USD ($) Lease	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015
Other Commitments [Line Items]
Rent expense			$ 1,100	$ 600	$ 400
Lease term			10 years 7 months
Lease commencement period			2019-05
Lessee, finance lease, existence of option to extend			true
Lessee, finance lease, existence of option to terminate			true
Options to extend terms of the lease			Two five-year
Initial annual base rent			$ 2,000
Payments for Tenant Improvements			2,700
Company capitalized construction-in-progress lease financing obligation			11,885
Current portion of the lease financing obligation			500
Long-term lease liability, net of current portion			11,347
Certificates of Deposit [Member] \| Letter of Credit [Member]
Other Commitments [Line Items]
Cash balance to secure letter of credit associated with lease			$ 1,100
KBA Grants [Member]
Other Commitments [Line Items]
Number of awards grants \| award	2
Amount of grants awarded	$ 2,000
Kansas(KS) [Member]
Other Commitments [Line Items]
Number of lease agreement \| Lease			2
Operating lease expiry date			Dec. 31, 2020
Lease term						5 years
Massachusetts (MA) [Member]
Other Commitments [Line Items]
Sublease term		9 months	3 years
Sublease expiration date		May 31, 2019	Sep. 30, 2019

Commitments and Contingencies - Summary of Future Minimum Lease Payments under Operating Leases (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019	$ 726
2020	333
Future minimum lease payments due	$ 1,059

Commitments and Contingencies - Future Minimum Lease Payments Commitments Lease (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Contractual Obligation, Fiscal Year Maturity Schedule [Abstract]
2019	$ 170
2020	2,043
2021	2,088
2022	2,132
2023	2,177
Thereafter	13,783
Total	$ 22,393

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Income tax benefits	$ 0
Federal statutory income tax rate	21.00%	34.00%
Percentage of net operating loss carry forward deductible from current year taxable income		80.00%
Decrease in deferred tax asset due to Tax Cuts and Jobs Act		$ 3,100,000
Tax Cuts And Jobs Act, incomplete accounting, provisional income tax expense (benefit)		0
Research and orphan drug credit carryforwards	$ 13,457,000	$ 3,888,000
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.
Maximum [Member]
Income Tax Disclosure [Line Items]
Federal statutory income tax rate		35.00%
Scenario, Plan [Member]
Income Tax Disclosure [Line Items]
Federal statutory income tax rate	21.00%
Earliest Tax Year [Member]
Income Tax Disclosure [Line Items]
Open tax year	2018
Latest Tax Year [Member]
Income Tax Disclosure [Line Items]
Open tax year	2018
Federal [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 107.1
Net operating loss carryforwards expiration year	2037
Research and orphan drug credit carryforwards	$ 12,800,000
Tax credit carryforwards expiration year	2037
Operating Loss Carryforwards, Subject to Expiration	$ 14.5
Operating Loss Carryforwards, Not Subject to Expiration	92.6
State [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 107.7
Net operating loss carryforwards expiration year	2027
Research and orphan drug credit carryforwards	$ 900,000
Tax credit carryforwards expiration year	2032

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

Income Taxes - Schedule of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets (liabilities):
Net operating loss carryforwards	$ 28,906	$ 4,030
Research and orphan drug credit carryforwards	13,457	3,888
Stock-based compensation	4,681	2,366
Accrued expenses and lease liability	4,470	672
Property and equipment	(3,200)	(129)
Other	(123)	8
Total gross deferred tax assets	48,191	10,835
Valuation allowance	(48,191)	(10,835)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Schedule of Changes in Valuation Allowance for Deferred Tax Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Valuation allowance as of beginning of year	$ (10,835)
Net increases recorded to income tax provision	(37,356)	$ (10,835)
Valuation allowance as of end of year	$ (48,191)	$ (10,835)

401(k) Savings Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Percentage of matching contribution to plan	50.00%
Clinical Reference Laboratory, Inc. [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan description	Effective January 1, 2018, the Company adopted the Deciphera Pharmaceuticals 401(k) plan (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.
Percentage of matching contribution to plan	100.00%
Matching contributions to the plan by employer	$ 400,000	$ 100,000
Maximum [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of salary for matching contribution per employee on time-based vesting	5.00%
Maximum [Member] \| Clinical Reference Laboratory, Inc. [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of matching contribution to plan	50.00%
Employee earnings subject to employer match	3.00%
Percentage of salary for matching contribution per employee	6.00%
Matching contributions to the plan by employer			$ 100,000
Minimum [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of salary for matching contribution per employee on time-based vesting	3.00%

Related Parties - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2010
Related Party Transaction [Line Items]
Research and development expense	$ 82,887,000	$ 39,514,000	$ 20,163,000
CRL Construction Loan [Member]
Related Party Transaction [Line Items]
Interest expense on borrowings	100,000	100,000	100,000
Principal amount owed under loan agreement	1,294,000	1,481,000
Clinical Reference Laboratory, Inc. [Member]
Related Party Transaction [Line Items]
Laboratory services	200,000	$ 100,000
Clinical Reference Laboratory, Inc. [Member] \| Loan and Security Agreement [Member]
Related Party Transaction [Line Items]
Aggregate borrowings	2,800,000			$ 2,800,000
Fixed interest rate				6.00%
Debt instrument payment term		15-year straight-line amortization schedule.
Debt instrument principal and interest payment	300,000	$ 300,000	300,000
Principal amount owed under loan agreement	1,300,000	1,500,000
Clinical Reference Laboratory, Inc. [Member] \| Service Agreement [Member]
Related Party Transaction [Line Items]
Research and development expense	900,000	400,000	200,000
Payments for research and development expense	$ 800,000	400,000	100,000
Employees contributions under 401(K) plan		600,000	$ 200,000
Clinical Reference Laboratory, Inc. [Member] \| CHC, Inc. [Member] \| Loan and Security Agreement [Member]
Related Party Transaction [Line Items]
Ownership percentage			100.00%
Fixed interest rate			6.00%
Debt instrument payment term	15-year straight-line amortization schedule
Debt instrument term	15 years
Clinical Reference Laboratory, Inc. [Member] \| Maximum [Member] \| CRL Construction Loan [Member]
Related Party Transaction [Line Items]
Interest expense on borrowings	$ 100,000	$ 100,000	$ 100,000
Clinical Reference Laboratory, Inc. [Member] \| Brightstar [Member]
Related Party Transaction [Line Items]
Ownership percentage	31.00%
Clinical Reference Laboratory, Inc. [Member] \| Brightstar [Member] \| Minimum [Member]
Related Party Transaction [Line Items]
Percentage of common stock holding	5.00%

Selected Quarterly Financial Data (Unaudited) - Schedule of Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statements of Operations Data:
Revenue	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Loss from operations	(33,830)	(25,889)	(22,429)	(21,951)	(20,338)	(12,181)	(10,691)	(7,725)	(104,099)	(50,935)	(25,838)
Net loss	$ (32,299)	$ (24,435)	$ (21,690)	$ (21,430)	$ (19,912)	$ (12,038)	$ (10,626)	$ (7,708)	$ (99,854)	$ (50,284)	$ (25,940)
Net loss per share - basic and diluted	$ (0.86)	$ (0.65)	$ (0.65)	$ (0.66)	$ (0.62)	$ (1.04)	$ (0.91)	$ (0.66)	$ (2.82)	$ (2.99)	$ (2.23)

- Definition

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

+ References + Details