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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2019	Apr. 30, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	DCPH
Entity Registrant Name	DECIPHERA PHARMACEUTICALS, INC.
Entity Central Index Key	0001654151
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Smaller Reporting Company	true
Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		38,189,052

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 82,228	$ 293,764
Marketable securities	180,114	0
Prepaid expenses and other current assets	4,103	7,273
Total current assets	266,445	301,037
Long-term investment-restricted	1,069	1,069
Property and equipment, net	1,504	13,453
Operating lease, right-of-use assets	670
Total assets	269,688	315,559
Current liabilities:
Accounts payable	10,937	8,308
Accrued expenses and other current liabilities	16,333	13,709
Operating lease liabilities	434	539
Notes payable to related party	187	187
Total current liabilities	27,891	22,743
Notes payable to related party, net of current portion	1,076	1,107
Operating lease liabilities, net of current portion	244	11,347
Other long-term liabilities	481	381
Total liabilities	29,692	35,578
Commitments and contingencies (Note 7)
Stockholders' equity:
Preferred stock value
Common stock value	382	377
Additional paid-in capital	582,700	575,327
Accumulated other comprehensive income	21
Accumulated deficit	(343,107)	(295,723)
Total stockholders' equity	239,996	279,981
Total liabilities and stockholders' equity	$ 269,688	$ 315,559

Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
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	38,189,052	37,676,760
Common stock, shares outstanding	38,189,052	37,676,760

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenue	$ 0	$ 0
Operating expenses:
Research and development	35,789	16,925
General and administrative	13,236	5,026
Total operating expenses	49,025	21,951
Loss from operations	(49,025)	(21,951)
Other income (expense):
Interest expense	(13)	(22)
Interest and other income, net	1,654	543
Total other income (expense), net	1,641	521
Net loss	$ (47,384)	$ (21,430)
Net loss per share-basic and diluted	$ (1.25)	$ (0.66)
Weighted average common shares outstanding-basic and diluted	38,057,018	32,594,074
Comprehensive loss:
Net loss	$ (47,384)	$ (21,430)
Other comprehensive income:
Unrealized gains on marketable securities	21
Total other comprehensive income	21
Total comprehensive loss	$ (47,363)	$ (21,430)

Consolidated Statements of Stockholders Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2017	$ 183,973	$ 326	$ 379,516		$ (195,869)
Beginning balance, shares at Dec. 31, 2017		32,591,686
Issuance of common stock upon exercise of stock options	10		10
Issuance of common stock upon exercise of stock options, Shares		2,442
Stock-based compensation expense	2,037		2,037
Net loss	(21,430)				(21,430)
Ending balance at Mar. 31, 2018	164,590	$ 326	381,563		(217,299)
Ending balance, shares at Mar. 31, 2018		32,594,128
Beginning balance at Dec. 31, 2017	183,973	$ 326	379,516		(195,869)
Beginning balance, shares at Dec. 31, 2017		32,591,686
Net loss	99,900
Ending balance at Dec. 31, 2018	279,981	$ 377	575,327		(295,723)
Ending balance, shares at Dec. 31, 2018		37,676,760
Issuance of common stock upon exercise of stock options	1,149	$ 5	1,144
Issuance of common stock upon exercise of stock options, Shares		512,292
Stock-based compensation expense	6,229		6,229
Unrealized gains on marketable securities	21			$ 21
Net loss	(47,384)				(47,384)
Ending balance at Mar. 31, 2019	$ 239,996	$ 382	$ 582,700	$ 21	$ (343,107)
Ending balance, shares at Mar. 31, 2019		38,189,052

- Definition

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

+ References + Details

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (47,384)	$ (21,430)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	6,229	2,037
Depreciation and amortization expense	104	56
Net accretion of discounts on marketable securities	(486)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	3,170	187
Operating lease, right-of-use assets	143
Accounts payable	2,629	1,142
Accrued expenses and other current liabilities	2,637	1,319
Operating lease liabilities	(148)
Other long-term liabilities	100	(5)
Net cash used in operating activities	(33,006)	(16,694)
Cash flows from investing activities:
Purchases of marketable securities	(179,607)
Purchases of property and equipment	(41)	(151)
Net cash used in investing activities	(179,648)	(151)
Cash flows from financing activities:
Repayment of notes payable to related party	(31)	(46)
Proceeds from exercise of stock options	1,149	10
Net cash provided by (used in) financing activities	1,118	(36)
Net decrease in cash and cash equivalents	(211,536)	(16,881)
Cash and cash equivalents at beginning of period	293,764	196,754
Cash and cash equivalents at end of period	82,228	179,873
Cash paid for interest	$ 13	22
Purchases of property and equipment included in accounts payable and accrued expenses		$ 97

Nature of the Business and Basis of Presentation	3 Months Ended
Nature of the Business and Basis of Presentation	Mar. 31, 2019
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 $47.4 million and $99.9 million for the three months ended March 31, 2019 and the year ended December 31, 2018, respectively. As of March 31, 2019, the Company had an accumulated deficit of $343.1 million. The Company expects to continue to generate operating losses in the foreseeable future. The Company expects that its cash, cash equivalents and marketable securities 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 and engages in efforts to support commercialization should ripretinib receive regulatory approval. Accordingly, the Company will need to obtain substantial additional funding in connection with continuing operations. If the Company is unable to raise capital when needed, or on attractive terms, it could be forced to delay, reduce or eliminate its research or drug development programs or any future commercialization efforts. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. These consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated. 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

3 Months Ended

Mar. 31, 2019

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 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.

Unaudited Interim Financial Information

The consolidated balance sheet at December 31, 2018 was derived from audited financial statements, but does not include all disclosures required by U.S. GAAP. The accompanying unaudited consolidated financial statements as of March 31, 2019 and for the three months ended March 31, 2019 and 2018 have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. The Company believes, however, that the disclosures are adequate to make the information presented not misleading. These consolidated financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2018 included in the Company’s Annual Report on Form 10-K on file with the SEC. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s consolidated financial position as of March 31, 2019 and consolidated results of operations for the three months ended March 31, 2019 and 2018 and consolidated cash flows for the three months ended March 31, 2019 and 2018 have been made. The consolidated results of operations for the three months ended March 31, 2019 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2019.

Fair Value Measurements

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

•

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

•

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

•

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

The Company’s cash equivalents and marketable securities are carried at fair value, determined according to the fair value hierarchy described above (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 a related party (see Note 5) as of each of March 31, 2019 and December 31, 2018 approximated $1.1 million. 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.

Leases

The Company accounts for a contract as a lease when it has the right to control the asset for a period of time while obtaining substantially all of the asset’s economic benefits. The Company determines if an arrangement is a lease or contains an embedded lease at inception. For arrangements that meet the definition of a lease, the Company determines the initial classification and measurement of its operating right-of-use asset and operating lease liability at the lease commencement date and thereafter if modified. The lease term includes any renewal options that the Company is reasonably assured to exercise. The present value of lease payments is determined by using the interest rate implicit in the lease, if that rate is readily determinable; otherwise, the Company uses its estimated secured incremental borrowing rate for that lease term. The Company’s policy is to not record leases with an original term of twelve months or less on its consolidated balance sheets and recognizes those lease payments in the income statement on a straight-line basis over the lease term. The Company’s only existing leases are for office and laboratory space.

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

Comprehensive Loss

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

Net Loss per Share

Basic net income (loss) per share is computed by dividing the net income (loss) by the weighted average number of common shares outstanding for the period. 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 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 reported a net loss for each of the three months ended March 31, 2019 and 2018.

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 March 31,
	2019		2018
Options to purchase common stock		6,713,029		5,374,080
Unvested restricted common stock units		77,000		—

		6,790,029		5,374,080

Recently Adopted Accounting Pronouncements

In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (“ASU 2016-02”). ASU 2016-02 requires lessees to recognize most leases on their balance sheet as a right-of-use asset and a lease liability. Leases are classified as either operating or finance, and classification is based on criteria similar to current lease accounting, but without explicit bright lines. The guidance is effective for annual reporting periods beginning after December 15, 2018 and interim periods within those fiscal years, and early adoption is permitted. 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 recognize a cumulative catch-up adjustment to the opening balance of retained earnings in the period of adoption. The Company adopted the new leasing standards on the effective date of January 1, 2019 using a modified retrospective approach applied at the beginning of the period of adoption.

The Company elected the “package of practical expedients”, which permits the Company not to reassess under the new standards for prior conclusions about lease identification, lease classification and initial direct costs. The Company did not apply the hindsight practical expedient when determining the lease term for existing leases and assessing impairment of expired or existing leases. The Company did not apply the recognition requirements to short-term leases and recognizes those lease payments in the consolidated statements of operations and comprehensive loss on a straight-line basis over the lease term. The Company elected the practical expedient to not separate lease andnon-lease components for real estate leases. The Company elected to utilize its incremental borrowing rate based on the remaining lease term as of the date of adoption.

In connection with the adoption, the Company recognized right-of-use assets of $0.8 million and lease liabilities of $0.8 million on its consolidated balance sheet. The underlying assets of the Company’s leases consist of office and laboratory space. In addition, the Company reversed its build to suit asset of $11.9 million and related liabilities of $11.9 million under the new guidance as the Company is no longer deemed the owner of the leased space (see Note 7). The adoption of the standard did not have a material impact on the Company’s 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 adopted ASU 2018-07 as of January 1, 2019 and it had no impact on the Company’s financial position, results of operations or cash flows.

Marketable Securities and Fair Value Measurements

3 Months Ended

Mar. 31, 2019

Investments, All Other Investments [Abstract]

Marketable Securities and Fair Value Measurements

3. Marketable Securities and Fair Value Measurements

As of March 31, 2019, marketable securities by security type consisted of (in thousands):


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Commercial paper (due within one year)	$	99,108	$	6	$	(23	)	$	99,091
U.S. Government securities (due within one year)		42,616		28		—			42,644
Certificates of deposit (due within one year)		38,369		10		—			38,379

Total	$	180,093	$	44	$	(23	)	$	180,114

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

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


	Fair Value Measurements at March 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	5,403	$	—	$	5,403
Commercial paper		—		49,219		—		49,219
Certificates of deposit		—		19,002		—		19,002
Marketable securities:
Commercial paper		—		99,091		—		99,091
U.S. Government securities		—		42,644		—		42,644
Certificates of deposit		—		38,379		—		38,379

Total	$	—	$	253,738	$	—	$	253,738


	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

The table above as of March 31, 2019 and December 31, 2018 excludes a certificate of deposit in the amount of $1.1 million that the Company held to secure a letter of credit associated with a lease (see Note 7).

During the three months ended March 31, 2019 and 2018, there were no transfers between Level 1, Level 2 and Level 3.

Accrued Expenses and Other Current Liabilities

3 Months Ended

Mar. 31, 2019

Payables and Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

4. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	March 31, 2019		December 31, 2018
Accrued external research and development expenses	$	11,653	$	8,761
Accrued payroll and related expenses		3,030		4,139
Accrued professional fees		1,468		747
Accrued other		182		62

	$	16,333	$	13,709

Notes Payable to Related Party

3 Months Ended

Mar. 31, 2019

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Notes Payable to Related Party

5. Notes Payable to Related Party

Notes payable to related party as of March 31, 2019 and December 31, 2018 consisted of outstanding borrowings under a loan agreement and a security agreement (together, the “CRL Construction Loan”) with Clinical Reference Laboratory, Inc. (“CRL”), a related party (see Note 9), as follows (in thousands):


	March 31, 2019			December 31, 2018
Notes payable to related party	$	1,263		$	1,294
Less: Current portion		(187	)		(187	)

Notes payable to related party, net of current portion	$	1,076		$	1,107

Total interest expense was less than $0.1 million for each of the three months ended March 31, 2019 and 2018.

Stock-Based Awards

3 Months Ended

Mar. 31, 2019

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

Stock-Based Awards

6. Stock-Based Awards

The Company grants stock-based awards under its 2017 Stock Option and Incentive Plan (the “2017 Plan”) and is authorized to issue common stock under its 2017 Employee Stock Purchase Plan (“ESPP”). The Company also has outstanding stock options under its 2015 Equity Incentive Plan but is no longer granting awards under this plan. As of March 31, 2019, 2,116,883 shares of common stock were available for issuance under the 2017 Plan. As of March 31, 2019, 1,009,433 shares of common stock were available for issuance to participating employees under the ESPP.

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


	Three Months Ended March 31,
	2019		2018
Research and development expenses	$	1,692	$	962
General and administrative expenses		4,537		1,075

	$	6,229	$	2,037

As of March 31, 2019, total unrecognized compensation cost related to the unvested share-based awards was $46.8 million, which is expected to be recognized over a weighted average of 2.9 years. During the three months ended March 31, 2019, the Company recorded $2.4 million of stock-based compensation expense related to the modification of stock options pursuant to the transition agreement with its former President and Chief Executive Officer.

Commitments and Contingencies

3 Months Ended

Mar. 31, 2019

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

7. 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. 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. The Company has two leases for additional office space in Lawrence, Kansas, that expire in December 2020. The lease agreements contain options to extend the lease terms however these extensions were not included in the right-of-use assets and lease liabilities as they were not reasonably certain of being exercised.

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 expense related to this sublease is included in short-term lease costs for the three months ended March 31, 2019. The Company’s leases require the Company to pay for certain operating expenses based on actual costs incurred and therefore as the amounts are variable in nature are expensed in the period incurred and included in variable lease costs for the three months ended March 31, 2019. Payment escalations specified in the lease are recognized on a straight-line basis over the lease terms.

The components of lease expense were as follows (in thousands):


	Three Months Ended March 31, 2019
Operating lease cost	$	155
Short-term lease cost		94
Variable lease cost		92

	$	341

Other information
Cash paid for amounts included in the measurement of operating lease liabilities	$	160
Operating lease liabilities arising from obtaining new right-of-use assets	$	—
Weighted-average remaining lease term—operating leases (in years)		1.51
Weighted-average discount rate—operating leases		5.91	%

Future annual minimum lease payments under operating leases as of March 31, 2019 were as follows (in thousands):


Remainder of 2019 (nine months)	$	378
2020		333

Total future minimum lease payments		711
Less: imputed interest		(33	)

Total operating lease liabilities	$	678

Included in the consolidated balance sheet:
Current operating lease liabilities	$	434
Operating lease liabilities, net of current portion		244

Total operating lease liabilities	$	678

As previously disclosed in the Company’s 2018 Annual Report on Form 10-K and under the previous lease accounting standard, ASC 840, Leases, the 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

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

Prior to the adoption of ASC 2016-02, the Company was deemed to be the owner of this leased space during the construction period because of certain provisions within the lease agreement. As a result, as of December 31, 2018, the Company capitalized approximately $11.9 million (equal to the estimated cost of its leased portion of the premises) as construction-in-progress within property and equipment and recorded a corresponding build-to-suitfacility lease financing obligation. Under ASC 2016-02, the Company is no longer considered the owner of the leased space and therefore the build-to suit asset and corresponding liabilities at December 31, 2018 were reversed as of the date of adoption on January 1, 2019. The Company expects to occupy this space in the third quarter of 2019 and is currently evaluating the lease commencement date and associated right-of-use asset and operating lease liabilities under ASC 2016-02.

As previously disclosed in the Company’s 2018 Annual Report on Form 10-K and under the previous lease accounting standard, ASC 840, Leases, as of December 31, 2018, minimum commitments under this lease were 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 Kansas Bioscience Authority, or 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 March 31, 2019 or December 31, 2018.

401(k) Savings Plan	3 Months Ended
401(k) Savings Plan	Mar. 31, 2019
Retirement Benefits [Abstract]
401(k) Savings Plan	8. 401(k) Savings Plan Effective January 1, 2018, the Company adopted the Deciphera Pharmaceuticals 401(k) Plan (the “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. Total employer matching contributions related to the 401(k) Plan were $0.3 million and $0.2 million, for the three months ended March 31, 2019 and 2018, respectively.

Related Parties	3 Months Ended
Related Parties	Mar. 31, 2019
Related Party Transactions [Abstract]
Related Parties	9. 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 three months ended March 31, 2019 and 2018, the Company recorded less than $0.1 million of interest expense related to this loan. For each of the three months ended March 31, 2019 and 2018, the Company made less than $0.1 million in principal and interest payments under the loan. As of March 31, 2019 and December 31, 2018, principal amounts owed under the loan agreement totaled $1.3 million (see Note 5). 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 certain laboratory testing needs. For each of the three months ended March 31, 2019 and 2018, the Company recorded $0.2 million of research and development expense incurred under this agreement, of which $0.2 million and less than $0.1 million, respectively, was paid to CRL during those same periods. As of March 31, 2019 and December 31, 2018, total amounts owed to CRL for laboratory services were $0.1 million and $0.2 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.

Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	10. Subsequent Events On April 29, 2019, the Company amended its lease for office space in Waltham, Massachusetts to add an additional 38,003 square feet of space for a total of 82,346 square feet of space. The lease term for the additional space is expected to commence on January 1, 2020 and expire on November 30, 2029. The Company is entitled to two five-year options to extend. The initial annual base rent for the additional space is approximately $1.9 million and will increase annually for a total of $18.2 million over the lease term. The Company will be required pay its share of operating expenses, taxes and other expenses related to the additional leased premises.

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Use of Estimates

Use of Estimates

Unaudited Interim Financial Information

Unaudited Interim Financial Information

Fair Value Measurements

Fair Value Measurements

•

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

•

Leases

Leases

Comprehensive Loss

Comprehensive Loss

Net Loss per Share

Net Loss per Share


	As of March 31,
	2019		2018
Options to purchase common stock		6,713,029		5,374,080
Unvested restricted common stock units		77,000		—

		6,790,029		5,374,080

Recently Adopted Accounting Pronouncements

Recently Adopted Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Summary of Potential Dilutive Securities


	As of March 31,
	2019		2018
Options to purchase common stock		6,713,029		5,374,080
Unvested restricted common stock units		77,000		—

		6,790,029		5,374,080

Marketable Securities and Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2019

Investments, All Other Investments [Abstract]

Schedule of Marketable Securities

As of March 31, 2019, marketable securities by security type consisted of (in thousands):


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Commercial paper (due within one year)	$	99,108	$	6	$	(23	)	$	99,091
U.S. Government securities (due within one year)		42,616		28		—			42,644
Certificates of deposit (due within one year)		38,369		10		—			38,379

Total	$	180,093	$	44	$	(23	)	$	180,114

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


	Fair Value Measurements at March 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	5,403	$	—	$	5,403
Commercial paper		—		49,219		—		49,219
Certificates of deposit		—		19,002		—		19,002
Marketable securities:
Commercial paper		—		99,091		—		99,091
U.S. Government securities		—		42,644		—		42,644
Certificates of deposit		—		38,379		—		38,379

Total	$	—	$	253,738	$	—	$	253,738


	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

Accrued Expenses and Other Current Liabilities (Tables)

3 Months Ended

Mar. 31, 2019

Payables and Accruals [Abstract]

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	March 31, 2019		December 31, 2018
Accrued external research and development expenses	$	11,653	$	8,761
Accrued payroll and related expenses		3,030		4,139
Accrued professional fees		1,468		747
Accrued other		182		62

	$	16,333	$	13,709

Notes Payable to Related Party (Tables)

3 Months Ended

Mar. 31, 2019

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Notes Payable to Related Party


	March 31, 2019			December 31, 2018
Notes payable to related party	$	1,263		$	1,294
Less: Current portion		(187	)		(187	)

Notes payable to related party, net of current portion	$	1,076		$	1,107

Stock-Based Awards (Tables)

3 Months Ended

Mar. 31, 2019

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

Classification of Stock-Based Compensation Expense

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


	Three Months Ended March 31,
	2019		2018
Research and development expenses	$	1,692	$	962
General and administrative expenses		4,537		1,075

	$	6,229	$	2,037

Commitments and Contingencies (Tables)

3 Months Ended

Mar. 31, 2019

Components of Lease Expense

The components of lease expense were as follows (in thousands):


	Three Months Ended March 31, 2019
Operating lease cost	$	155
Short-term lease cost		94
Variable lease cost		92

	$	341

Other information
Cash paid for amounts included in the measurement of operating lease liabilities	$	160
Operating lease liabilities arising from obtaining new right-of-use assets	$	—
Weighted-average remaining lease term—operating leases (in years)		1.51
Weighted-average discount rate—operating leases		5.91	%

Summary of Future Minimum Lease Payments under Operating Leases

Future annual minimum lease payments under operating leases as of March 31, 2019 were as follows (in thousands):


Remainder of 2019 (nine months)	$	378
2020		333

Total future minimum lease payments		711
Less: imputed interest		(33	)

Total operating lease liabilities	$	678

Included in the consolidated balance sheet:
Current operating lease liabilities	$	434
Operating lease liabilities, net of current portion		244

Total operating lease liabilities	$	678

Accounting Standards Update 2016-02 [Member]

Summary of Future Minimum Lease Payments under Operating Leases


Year Ending December 31,
2019	$	726
2020		333

	$	1,059

Summary of Future Minimum Lease Payments


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

	$	22,393

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
	Oct. 02, 2017	Jun. 30, 2018 USD ($) $ / shares shares	Oct. 31, 2017 USD ($) $ / shares shares	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Nature Of Business And Basis Of Presentation [Line Items]
Share conversion ratio	5.65
Accumulated deficit				$ (343,107)		$ (295,723)
Net loss				$ (47,384)	$ (21,430)	$ 99,900
Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Net proceeds from initial public offering		$ 185,300
IPO [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Number of shares issued and sold \| shares			8,166,496
Additional offering price of common stock \| $ / shares			$ 17.00
Net proceeds from initial public offering			$ 124,600
IPO [Member] \| Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Number of shares issued and sold \| shares		4,945,000
Additional offering price of common stock \| $ / shares		$ 40.00

- Definition

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

+ References + Details

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Right of use assets	$ 670
Lease liabilities	678	$ 11,900
Construction in Progress [Member]
Significant Accounting Policies [Line Items]
Company capitalized construction-in-progress lease financing obligation		11,900
Accounting Standards Update 2016-02 [Member]
Significant Accounting Policies [Line Items]
Right of use assets	800
Lease liabilities	800
CRL Construction Loan [Member]
Significant Accounting Policies [Line Items]
Fair value of outstanding notes payable to related party	$ 1,100	$ 1,100

Summary of Significant Accounting Policies - Summary of Potential Dilutive Securities (Detail) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share	6,790,029	5,374,080
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	77,000
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	6,713,029	5,374,080

Marketable Securities and Fair Value Measurements - Schedule of Marketable Securities (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Fair Value Measurements Of Financial Instruments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 180,093
Debt Securities, Available-for-sale, Gross Unrealized Gains	44
Debt Securities, Available-for-sale, Gross Unrealized Losses	(23)
Debt Securities, Available-for-sale, Estimated Fair Value	180,114
Commercial Paper [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	99,108
Debt Securities, Available-for-sale, Gross Unrealized Gains	6
Debt Securities, Available-for-sale, Gross Unrealized Losses	(23)
Debt Securities, Available-for-sale, Estimated Fair Value	99,091
US Government Debt Securities [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	42,616
Debt Securities, Available-for-sale, Gross Unrealized Gains	28
Debt Securities, Available-for-sale, Estimated Fair Value	42,644
Certificates of Deposit [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	38,369
Debt Securities, Available-for-sale, Gross Unrealized Gains	10
Debt Securities, Available-for-sale, Estimated Fair Value	$ 38,379

Marketable Securities and Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Fair Value of Assets and Liabilities Measured on Non Recurring Basis [Line Items]
Marketable securities	$ 180,114,000		$ 0
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		$ 1,100,000

Marketable Securities and Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Cash equivalents:
Total Cash equivalents		$ 267,145
Marketable securities:
Total	$ 253,738
Commercial Paper [Member]
Marketable securities:
Total Marketable securities	99,091
US Government Debt Securities [Member]
Marketable securities:
Total Marketable securities	42,644
Certificates of Deposit [Member]
Marketable securities:
Total Marketable securities	38,379
Money Market Funds [Member]
Cash equivalents:
Total Cash equivalents	5,403	267,145
Commercial Paper [Member]
Cash equivalents:
Total Cash equivalents	49,219
Certificates of Deposit [Member]
Cash equivalents:
Total Cash equivalents	19,002
Level 2 [Member]
Cash equivalents:
Total Cash equivalents		267,145
Marketable securities:
Total	253,738
Level 2 [Member] \| Commercial Paper [Member]
Marketable securities:
Total Marketable securities	99,091
Level 2 [Member] \| US Government Debt Securities [Member]
Marketable securities:
Total Marketable securities	42,644
Level 2 [Member] \| Certificates of Deposit [Member]
Marketable securities:
Total Marketable securities	38,379
Level 2 [Member] \| Money Market Funds [Member]
Cash equivalents:
Total Cash equivalents	5,403	$ 267,145
Level 2 [Member] \| Commercial Paper [Member]
Cash equivalents:
Total Cash equivalents	49,219
Level 2 [Member] \| Certificates of Deposit [Member]
Cash equivalents:
Total Cash equivalents	$ 19,002

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts Payable and Accrued Liabilities [Abstract]
Accrued external research and development expenses	$ 11,653	$ 8,761
Accrued payroll and related expenses	3,030	4,139
Accrued professional fees	1,468	747
Accrued other	182	62
Accrued expenses and other current liabilities	$ 16,333	$ 13,709

Notes Payable to Related Party - Schedule of Notes Payable to Related Party (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Less: Current portion	$ (187)	$ (187)
Notes payable to related party, net of current portion	1,076	1,107
CRL Construction Loan [Member] \| Clinical Reference Laboratory, Inc. [Member]
Related Party Transaction [Line Items]
Notes payable to related party	1,263	1,294
Less: Current portion	(187)	(187)
Notes payable to related party, net of current portion	$ 1,076	$ 1,107

Notes Payable to Related Party - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Maximum [Member] \| Clinical Reference Laboratory, Inc. [Member] \| CRL Construction Loan [Member]
Related Party Transaction [Line Items]
Total interest expense	$ 100,000	$ 100,000

Stock-Based Awards - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested share-based awards \| $	$ 46.8
Unrecognized compensation cost related to unvested share-based awards, period for recognition	2 years 10 months 24 days
President And Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense related to modification \| $	$ 2.4
2017 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for issuance \| shares	2,116,883
Employee Stock Purchase Plan (ESPP) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for issuance \| shares	1,009,433

Stock-Based Awards - Classification of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 6,229	$ 2,037
Research and Development Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	1,692	962
General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 4,537	$ 1,075

Commitments and Contingencies - Additional Information (Detail) $ in Millions		1 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2013 USD ($) award	Aug. 30, 2018	Dec. 31, 2015 Lease	Mar. 31, 2019 USD ($) Lease	Dec. 31, 2018 USD ($)
Other Commitments [Line Items]
Lease commencement period				2019
Lease expiration period				2029-11
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				$ 2.0
Total operating lease rent expense				22.4
Company capitalized construction-in-progress lease financing obligation					$ 11.9
Cash [Member] \| Letter of Credit [Member]
Other Commitments [Line Items]
Cash balance to secure letter of credit associated with lease				$ 1.1
KBA Grants [Member]
Other Commitments [Line Items]
Number of awards grants \| award	2
Amount of grants awarded	$ 2.0
Kansas(KS) [Member] \| Lease Agreement for Office and Laboratory Space in Lawrence, Kansas [Member]
Other Commitments [Line Items]
Number of lease agreement \| Lease			2
Operating lease expiry date			Dec. 31, 2020
Lease term			5 years
Kansas(KS) [Member] \| Lease for Additional Office Space in Lawrence, Kansas [Member]
Other Commitments [Line Items]
Number of lease agreement \| Lease				2
Operating lease expiry date				Dec. 31, 2020
Massachusetts (MA) [Member] \| Sublease Agreement for Office Space in Waltham, Massachusetts [Member]
Other Commitments [Line Items]
Sublease term				3 years
Sublease expiration date				Sep. 30, 2019
Massachusetts (MA) [Member] \| Sublease for Additional Agreement for Office Space in Waltham, Massachusetts [Member]
Other Commitments [Line Items]
Sublease term		9 months
Sublease expiration date		May 31, 2019

Commitments and Contingencies - Components of Lease Expense (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Leases, Operating [Abstract]
Operating lease cost	$ 155
Short-term lease cost	94
Variable lease cost	92
Total lease cost	341
Cash paid for amounts included in the measurement of operating lease liabilities	160
Operating lease liabilities arising from obtaining new right-of-use assets	$ 0
Weighted-average remaining lease term-operating leases (in years)	1 year 6 months 3 days
Weighted-average discount rate-operating leases	5.91%

Commitments and Contingencies - Summary of Future Minimum Lease Payments under Operating Leases (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Remainder of 2019 (nine months)	$ 378
2019		$ 726
2020	333	333
Future minimum lease payments due	711	1,059
Less: imputed interest	(33)
Total operating lease liabilities	678	11,900
Current operating lease liabilities	434	539
Operating lease liabilities, net of current portion	244	11,347
Total operating lease liabilities	$ 678	$ 11,900

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

401(k) Savings Plan - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
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 "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	$ 0.3	$ 0.2
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]
Employee earnings subject to employer match	3.00%
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 ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Related Party Transaction [Line Items]
Research and development expense	$ 35,789,000	$ 16,925,000
Clinical Reference Laboratory, Inc. [Member]
Related Party Transaction [Line Items]
Laboratory services	100,000		$ 200,000
Clinical Reference Laboratory, Inc. [Member] \| Loan and Security Agreement [Member]
Related Party Transaction [Line Items]
Aggregate borrowings	2,800,000
Debt instrument principal and interest payment	100,000	100,000
Principal amount owed under loan agreement	1,300,000		1,300,000
Clinical Reference Laboratory, Inc. [Member] \| Service Agreement [Member]
Related Party Transaction [Line Items]
Research and development expense	200,000	200,000
Payments for research and development expense	$ 200,000	$ 100,000
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] \| CRL Construction Loan [Member]
Related Party Transaction [Line Items]
Principal amount owed under loan agreement	$ 1,263,000		$ 1,294,000
Clinical Reference Laboratory, Inc. [Member] \| Maximum [Member] \| CRL Construction Loan [Member]
Related Party Transaction [Line Items]
Interest expense on borrowings	$ 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%

Subsequent Events - Additional Information (Detail) $ in Millions		3 Months Ended
	Apr. 29, 2019 USD ($) ft²	Mar. 31, 2019 USD ($)
Subsequent Event [Line Items]
Total operating lease over the lease term		$ 2.0
Subsequent Event [Member] \| Office Space in Waltham [Member] \| Massachusetts [Member]
Subsequent Event [Line Items]
Additional area of lease space \| ft²	38,003
Total lease area \| ft²	82,346
Lease commencement date	Jan. 01, 2020
Lease expiation date	Nov. 30, 2029
Lessee, operating lease, existence of option to extend	true
Options to extend terms of the lease	Two five-year
Options to extend terms of the lease	5 years
Initial annual base rent for the additional space	$ 1.9
Total operating lease over the lease term	$ 18.2