Mirati Therapeutics (MRTX) 10-Q 4 Nov 19 2019 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2019	Oct. 30, 2019
Cover page.
Entity Central Index Key	0001576263
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	001-35921
Entity Registrant Name	Mirati Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-2693615
Entity Address, Address Line One	9393 Towne Centre Drive, Suite 200
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92121
City Area Code	858
Local Phone Number	332-3410
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	MRTX
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		39,436,402

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 91,904	$ 32,694
Short-term investments	362,308	190,096
Other current assets	10,436	3,870
Total current assets	464,648	226,660
Property and equipment, net	536	473
Other long-term assets	5,514	1,321
Total assets	470,698	228,454
Current liabilities
Accounts payable and accrued liabilities	34,689	25,775
Deferred revenue and other current liabilities	647	371
Total current liabilities	35,336	26,146
Deferred revenue and other liabilities	873	732
Total liabilities	36,209	26,878
Commitments and contingencies (see Note 11)
Stockholders’ equity
Preferred stock, $0.001 par value; 10,000,000 shares authorized; none issued and outstanding at both September 30, 2019 and December 31, 2018	0	0
Common stock, $0.001 par value; 100,000,000 shares authorized; 39,367,683 and 32,538,857 issued and outstanding at September 30, 2019 and December 31, 2018, respectively	39	33
Additional paid-in capital	1,124,484	751,109
Accumulated other comprehensive income	9,891	9,479
Accumulated deficit	(699,925)	(559,045)
Total stockholders’ equity	434,489	201,576
Total liabilities and stockholders’ equity	$ 470,698	$ 228,454

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Preferred stock, par value (USD per share)	$ 0.001	$ 0.001
Preferred stock authorized (shares)	10,000,000	10,000,000
Preferred stock issued (shares)	0	0
Preferred stock outstanding (shares)	0	0
Common stock, par value (USD per share)	$ 0.001	$ 0.001
Common stock authorized (shares)	100,000,000	100,000,000
Common stock issued (shares)	39,367,683	32,538,857
Common stock outstanding (shares)	39,367,683	32,538,857

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue
License and collaboration revenues	$ 988	$ 0	$ 2,809	$ 9,467
Total revenue	988	0	2,809	9,467
Operating expenses
Research and development	47,362	23,626	119,925	67,114
General and administrative	10,685	5,313	30,340	15,308
Total operating expenses	58,047	28,939	150,265	82,422
Loss from operations	(57,059)	(28,939)	(147,456)	(72,955)
Other income, net	2,786	1,371	6,576	2,809
Net loss	(54,273)	(27,568)	(140,880)	(70,146)
Unrealized gain (loss) on available-for-sale investments	103	99	412	(35)
Comprehensive loss	$ (54,170)	$ (27,469)	$ (140,468)	$ (70,181)
Basic and diluted net loss per share (USD per share)	$ (1.38)	$ (0.85)	$ (3.83)	$ (2.31)
Weighted average number of shares used in computing net loss per share, basic and diluted (shares)	39,197,213	32,410,407	36,799,173	30,350,389

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional paid-in capital	Accumulated other comprehensive income	Accumulated deficit
Balance at beginning of period (shares) at Dec. 31, 2017		28,622,886
Balance at beginning of period at Dec. 31, 2017	$ 143,288	$ 29	$ 594,407	$ 9,479	$ (460,627)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	(14,709)				(14,709)
Share-based compensation expense	3,660		3,660
Exercise of options for cash (shares)		402,948
Exercise of options for cash	5,890		5,890
Unrealized gain (loss) on investments	(288)			(288)
Balance at end of period (shares) at Mar. 31, 2018		29,025,834
Balance at end of period at Mar. 31, 2018	137,841	$ 29	603,957	9,191	(475,336)
Balance at beginning of period (shares) at Dec. 31, 2017		28,622,886
Balance at beginning of period at Dec. 31, 2017	143,288	$ 29	594,407	9,479	(460,627)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	$ (70,146)
Exercise of options for cash (shares)	716,409
Unrealized gain (loss) on investments	$ (35)
Balance at end of period (shares) at Sep. 30, 2018		32,516,041
Balance at end of period at Sep. 30, 2018	225,089	$ 33	746,385	9,444	(530,773)
Balance at beginning of period (shares) at Mar. 31, 2018		29,025,834
Balance at beginning of period at Mar. 31, 2018	137,841	$ 29	603,957	9,191	(475,336)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	(27,869)				(27,869)
Issuance of common stock, net of issuance costs (shares)		3,162,500
Issuance of common stock, net of issuance costs	130,660	$ 3	130,657
Share-based compensation expense	3,874		3,874
Issuance of common stock from ESPP (shares)		14,246
Issuance of common stock from ESPP	202		202
Exercise of options for cash (shares)		110,860
Exercise of options for cash	1,482		1,482
Unrealized gain (loss) on investments	154			154
Balance at end of period (shares) at Jun. 30, 2018		32,313,440
Balance at end of period at Jun. 30, 2018	246,344	$ 32	740,172	9,345	(503,205)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	(27,568)				(27,568)
Share-based compensation expense	$ 4,058		4,058
Exercise of options for cash (shares)	202,601	202,601
Exercise of options for cash	$ 2,156	$ 1	2,155
Unrealized gain (loss) on investments	99			99
Balance at end of period (shares) at Sep. 30, 2018		32,516,041
Balance at end of period at Sep. 30, 2018	$ 225,089	$ 33	746,385	9,444	(530,773)
Balance at beginning of period (shares) at Dec. 31, 2018	32,538,857	32,538,857
Balance at beginning of period at Dec. 31, 2018	$ 201,576	$ 33	751,109	9,479	(559,045)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	(40,912)				(40,912)
Issuance of common stock, net of issuance costs (shares)		1,854,838
Issuance of common stock, net of issuance costs	107,883	$ 2	107,881
Share-based compensation expense	11,131		11,131
Exercise of options for cash (shares)		235,398
Exercise of options for cash	2,668		2,668
Proceeds from disgorgement of stockholders' short-swing profits	1,050		1,050
Net exercise of warrants (shares)		1,400,000
Net exercise of warrants	0	$ 1	(1)
Unrealized gain (loss) on investments	158			158
Balance at end of period (shares) at Mar. 31, 2019		36,029,093
Balance at end of period at Mar. 31, 2019	$ 283,554	$ 36	873,838	9,637	(599,957)
Balance at beginning of period (shares) at Dec. 31, 2018	32,538,857	32,538,857
Balance at beginning of period at Dec. 31, 2018	$ 201,576	$ 33	751,109	9,479	(559,045)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	$ (140,880)
Exercise of options for cash (shares)	424,144
Net exercise of warrants (shares)	2,125,000
Unrealized gain (loss) on investments	$ 412
Balance at end of period (shares) at Sep. 30, 2019	39,367,683	39,367,683
Balance at end of period at Sep. 30, 2019	$ 434,489	$ 39	1,124,484	9,891	(699,925)
Balance at beginning of period (shares) at Mar. 31, 2019		36,029,093
Balance at beginning of period at Mar. 31, 2019	283,554	$ 36	873,838	9,637	(599,957)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	(45,695)				(45,695)
Issuance of common stock, net of issuance costs (shares)		2,415,000
Issuance of common stock, net of issuance costs	219,927	$ 3	219,924
Share-based compensation expense	12,589		12,589
Issuance of common stock from ESPP (shares)		9,844
Issuance of common stock from ESPP	323		323
Exercise of options for cash (shares)		97,489
Exercise of options for cash	1,632		1,632
Unrealized gain (loss) on investments	151			151
Balance at end of period (shares) at Jun. 30, 2019		38,551,426
Balance at end of period at Jun. 30, 2019	472,481	$ 39	1,108,306	9,788	(645,652)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	(54,273)				(54,273)
Share-based compensation expense	$ 15,106		15,106
Exercise of options for cash (shares)	91,257	91,257
Exercise of options for cash	$ 1,072		1,072
Net exercise of warrants (shares)	725,000	725,000
Net exercise of warrants	$ 0
Unrealized gain (loss) on investments	$ 103			103
Balance at end of period (shares) at Sep. 30, 2019	39,367,683	39,367,683
Balance at end of period at Sep. 30, 2019	$ 434,489	$ 39	$ 1,124,484	$ 9,891	$ (699,925)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018
Operating activities:
Net loss		$ (140,880)	$ (70,146)
Non-cash adjustments reconciling net loss to operating cash flows:
Depreciation of property and equipment		156	131
Accretion of discount on investments		(2,818)	(757)
Share-based compensation expense		38,826	11,592
Changes in operating assets and liabilities:
Other current assets		(6,566)	1,437
Other long-term assets		(3,873)	(204)
Accounts payable, accrued liabilities, deferred revenue and other liabilities		9,331	8,646
Cash flows used in operating activities		(105,824)	(49,301)
Investing activities:
Purchases of short-term investments		(458,115)	(155,775)
Sales and maturities of short-term investments		289,134	73,729
Purchases of property, plant, and equipment		(220)	(36)
Cash flows used in investing activities		(169,201)	(82,082)
Financing activities:
Proceeds from issuance of common stock, net of issuance costs	[1]	327,810	130,663
Proceeds from exercise of common stock options		5,372	9,525
Proceeds from disgorgement of stockholders' short-swing profits		1,050	0
Proceeds from stock issuances under ESPP		323	202
Cash flows provided by financing activities		334,555	140,390
Increase in cash, cash equivalents and restricted cash		59,530	9,007
Cash, cash equivalents and restricted cash, beginning of period		32,694	107,703
Cash, cash equivalents and restricted cash, end of period		92,224	116,710
Reconciliation of cash, cash equivalents and restricted cash, end of period:
Total cash, cash equivalents and restricted cash		$ 32,694	$ 107,703
[1]	Proceeds in 2018 include warrants to purchase up to 421,650 shares of the Company's common stock at a public offering price of $38.849 per warrant, net of issuance costs.

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - $ / shares	1 Months Ended
	Jun. 30, 2019	Jan. 31, 2019	Jun. 30, 2018
Stock issued in transaction (shares)	2,415,000	1,854,838	3,162,500
Sale price of common stock (USD per share)	$ 97	$ 62	$ 38.85
Note Warrant
Stock issued in transaction (shares)			421,650
Sale price of common stock (USD per share)			$ 38.849

Description of Business

Description of Business	9 Months Ended
	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of Business Mirati Therapeutics, Inc. ("Mirati" or the "Company") is a clinical-stage oncology company developing product candidates to address the genetic and immunological promoters of cancer. The Company was incorporated under the laws of the State of Delaware on April 29, 2013 as Mirati Therapeutics, Inc. and is located in San Diego, California. The Company has a wholly owned subsidiary in Canada, MethylGene, Inc., and operates in one

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The unaudited condensed consolidated financial statements contained in this Quarterly Report on Form 10-Q have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission ("SEC") and, therefore, certain information and disclosures normally included in annual financial statements prepared in accordance with accounting principles generally accepted in the United States of America ("U.S. GAAP") have been omitted. In the opinion of management, the information reflects all adjustments necessary to make the results of operations for the interim periods a fair statement of such operations. All such adjustments are of a normal recurring nature. Interim results are not necessarily indicative of results for the full year. The condensed consolidated balance sheet at December 31, 2018 has been derived from the audited consolidated financial statements at that date, but does not include all information and footnotes required by U.S. GAAP for complete financial statements. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements included in the Company's Annual Report on Form 10-K for the fiscal year ended December 31, 2018 . Use of Estimates The preparation of the Company's unaudited condensed consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. Reported amounts and note disclosures reflect the overall economic conditions that are most likely to occur and anticipated measures management intends to take. Actual results could differ materially from those estimates. Estimates and assumptions are reviewed quarterly. Any revisions to accounting estimates are recognized in the period in which the estimates are revised and in any future periods affected. Cash, Cash Equivalents and Short-term Investments Cash and cash equivalents consist of cash and highly liquid securities with original maturities at the date of acquisition of ninety days or less. Investments with an original maturity of more than ninety days are considered short-term investments and have been classified by management as available-for-sale. These investments are classified as current assets, even though the stated maturity date may be one year or more beyond the current balance sheet date, which reflects management’s intention to use the proceeds from sales of these securities to fund its operations, as necessary. Such investments are carried at fair value, and the unrealized gains and losses are reported as a component of accumulated other comprehensive income in stockholders’ equity until realized. Realized gains and losses from the sale of available-for-sale securities, if any, are determined on a specific identification basis. Concentration of Credit Risk The Company invests its excess cash in accordance with its investment policy. The Company's investments are comprised primarily of commercial paper and debt instruments of financial institutions, corporations, U.S. government-sponsored agencies and the U.S. Treasury. The Company mitigates credit risk by maintaining a diversified portfolio and limiting the amount of investment exposure as to institution, maturity and investment type. Financial instruments that potentially subject the Company to significant credit risk consist principally of cash equivalents and short-term investments. Revenue Recognition The Company recognizes revenue in connection with a collaboration and license agreement in accordance with the guidance of Revenue From Contracts With Customers, Accounting Standards Codification ("ASC") Topic 606 ("Topic 606"). Under Topic 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements the Company determines are within the scope of Topic 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. See Note 9 for a complete discussion of the revenue recognition for the Company’s collaboration and license agreement. Net loss per share Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration for common share equivalents. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and common share equivalents outstanding for the period. Common share equivalents outstanding, determined using the treasury stock method, are comprised of shares that may be issued under the Company’s stock option and warrant agreements. The following table presents the weighted-average number of common share equivalents, calculated using the treasury stock method, not included in the calculation of diluted net loss per share due to the anti-dilutive effect of the securities: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Common stock options 2,487,135 2,215,086 2,398,467 1,835,879 Common stock warrants 9,826,743 11,817,700 10,412,385 11,568,961 Total 12,313,878 14,032,786 12,810,852 13,404,840

Recently Adopted and Recently I

Recently Adopted and Recently Issued Accounting Pronouncements	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Recently Adopted and Recently Issued Accounting Pronouncements	Recently Adopted and Recently Issued Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board ("FASB") or other standard setting bodies that are adopted by the Company as of the specified effective date. Recently Adopted Accounting Pronouncements In February 2016, the FASB issued Accounting Standards Update ("ASU") 2016-02, Leases (Topic 842) in order to increase transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet for those leases classified as operating leases under previous GAAP. ASU 2016-02 requires a lessee to recognize a liability for lease payments (the lease liability) and a right-of-use asset (representing its right to use the underlying asset for the lease term) on the balance sheet. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018 (including interim periods within those periods) using a modified retrospective approach. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements , which provides entities an optional transition method to apply the new guidance as of the adoption date, rather than as of the earliest period presented. In transition, entities may also elect a package of practical expedients that must be applied in its entirety to all leases commencing before the effective date, unless the lease was modified, to not reassess (a) the existence of a lease, (b) lease classification or (c) determination of initial direct costs, which effectively allows entities to carryforward accounting conclusions under previous U.S. GAAP. The Company adopted ASU 2016-02, using the optional transition method and electing the package of practical expedients described above on January 1, 2019. Due to the adoption, the Company recognized a new lease liability on the Company's consolidated balance sheet for its operating lease of office and lab space of $367,000 on January 1, 2019, with a corresponding right-of-use asset of the same amount based on the present value of the remaining minimum rental payments. See Note 11 for further discussion. In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260); Distinguishing Liabilities from Equity (Topic 480); Derivatives and Hedging (Topic 815): (Part I) Accounting for Certain Financial Instruments with Down Round Features, (Part II) Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Non-controlling Interests with a Scope Exception . This ASU allows companies to exclude a down round feature when determining whether a financial instrument (or embedded conversion feature) is considered indexed to the entity’s own stock. As a result, financial instruments (or embedded conversion features) with down round features may no longer be required to be classified as liabilities. A company will recognize the value of a down round feature only when it is triggered and the strike price has been adjusted downward. For equity-classified freestanding financial instruments, such as warrants, an entity will treat the value of the effect of the down round, when triggered, as a dividend and a reduction of income available to common shareholders in computing basic earnings per share. For convertible instruments with embedded conversion features containing down round provisions, entities will recognize the value of the down round as a beneficial conversion discount to be amortized to earnings. Effective January 1, 2019, the Company adopted the provisions of ASU 2017-11. The adoption did not have a material impact on the Company's consolidated financial statements or related financial statement disclosures. On August 17, 2018, the SEC adopted amendments to certain disclosure requirements in Securities Act Release No. 33-10532, Disclosure Update and Simplification. Among the amendments is the requirement to present the changes in stockholders’ equity in the interim financial statements (either in a separate statement or footnote) in quarterly reports on Form 10-Q. The amendments are effective for all filings made on or after November 5, 2018. In light of the timing of effectiveness of the amendments and proximity of effectiveness to the filing date for most filers’ quarterly reports, the SEC indicated it would not object if the filer’s first presentation of the changes in stockholders’ equity is included in its Form 10-Q for the quarter that begins after the effective date of the amendments. The Company began including a condensed consolidated statement of changes in stockholders' equity in the Company's consolidated financial statements for the three months ended March 31, 2019 and 2018, and has included a condensed consolidated statement of changes in stockholders' equity in the Company's consolidated financial statements for the nine months ended September 30, 2019 and 2018 herein. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 . The amendments provide guidance on whether certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606. It also specifically (i) addresses when the participant should be considered a customer in the content of a unit of account, (ii) adds unit-of-account guidance in ASC 808 to align with guidance with ASC 606, and (iii) precludes presenting revenue from a collaborative arrangement together with revenue recognized under ASC 606 if the collaborative arrangement participant is not a customer. The guidance in ASU 2018-18 is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. Early adoption is permitted and should be applied retrospectively. The Company elected to early adopt this guidance effective January 1, 2019. The adoption had no impact on the Company's consolidated financial statements. Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments , which changes the impairment model for most financial assets and certain other instruments. For trade receivables and other instruments, entities will be required to use a new forward-looking expected loss model that generally will result in the earlier recognition of allowances for losses. For available-for-sale debt securities with unrealized losses, the losses will be recognized as allowances rather than as reductions in the amortized cost of the securities. This guidance is effective for annual reporting periods beginning after December 15, 2019, including interim periods within those years, with early adoption permitted only as of annual reporting periods beginning after December 15, 2018. The Company is currently evaluating the impact of the adoption of this guidance on the Company’s consolidated financial statements. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement . The new guidance modifies the disclosure requirements on fair value measurements in Topic 820. The amendments in ASU 2018-13 are effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company does not anticipate that the adoption of ASU 2018-13 will have a material impact on the Company's consolidated financial statements or related financial statement disclosures.

Short-term Investments

Short-term Investments	9 Months Ended
	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Short-term Investments	Short-term Investments The following tables summarize the Company's short-term investments (dollars in thousands): As of September 30, 2019 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 2 years or less $ 180,580 $ 271 $ (3 ) $ 180,848 Commercial paper 1 year or less 110,918 67 — 110,985 U.S. Agency bonds 2 years or less 37,500 21 — 37,521 U.S. Treasury bills 1 year or less 32,943 21 (10 ) 32,954 $ 361,941 $ 380 $ (13 ) $ 362,308 As of December 31, 2018 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 1 year or less $ 111,933 $ 26 $ (43 ) $ 111,916 Commercial paper 1 year or less 74,433 — (24 ) 74,409 U.S. Treasury bills 1 year or less 3,771 — — 3,771 $ 190,137 $ 26 $ (67 ) $ 190,096 The Company has classified all of its investment securities as available-for-sale as the sale of such securities may be required prior to maturity to implement management strategies, and accordingly, carries these investments at fair value. Unrealized gains and losses on available-for-sale securities are included as a component of comprehensive loss. At September 30, 2019

Fair value measurements

Fair value measurements	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair value measurements	Fair value measurements The Company has certain financial assets and liabilities recorded at fair value which have been classified as Level 1 or 2 within the fair value hierarchy as described in the accounting standards for fair value measurements. The authoritative guidance for fair value measurements defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or the most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact, and (iv) willing to transact. The guidance prioritizes the inputs used in measuring fair value into the following hierarchy: • Level 1- Quoted prices (unadjusted) in active markets for identical assets or liabilities; • Level 2- Inputs other than quoted prices included within Level 1 that are either directly or indirectly observable; and • Level 3- Unobservable inputs in which little or no market activity exists, therefore requiring an entity to develop its own assumptions about the assumptions that market participants would use in pricing. The following tables summarize the assets measured at fair value on a recurring basis (in thousands): September 30, 2019 Total Level 1 Level 2 Assets Cash and cash equivalents: Cash $ 3,078 $ 3,078 $ — Money market funds 88,826 88,826 — Total cash and cash equivalents 91,904 91,904 — Short-term investments: U.S. Treasury bills 32,954 32,954 — Corporate debt securities 180,848 — 180,848 Commercial paper 110,985 — 110,985 U.S. Agency bonds 37,521 — 37,521 Total short-term investments 362,308 32,954 329,354 Total $ 454,212 $ 124,858 $ 329,354 December 31, 2018 Total Level 1 Level 2 Assets Cash and cash equivalents: Cash $ 3,731 $ 3,731 $ — Money market funds 28,963 28,963 — Total cash and cash equivalents 32,694 32,694 — Short-term investments: U.S. Treasury bills 3,771 3,771 — Corporate debt securities 111,916 — 111,916 Commercial paper 74,409 — 74,409 Total short-term investments 190,096 3,771 186,325 Total $ 222,790 $ 36,465 $ 186,325 The Company’s investments in Level 1 assets are valued based on publicly available quoted market prices for identical securities as of September 30, 2019 and December 31, 2018 . The Company determines the fair value of Level 2 related securities with the aid of valuations provided by third parties using proprietary valuation models and analytical tools. These valuation models and analytical tools use market pricing or prices for similar instruments that are both objective and publicly available, including matrix pricing or reported trades, benchmark yields, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids and/or offers. There were no transfers between fair value measurement levels during the three and nine months ended September 30, 2019 or the year ended December 31, 2018

Other current assets and other

Other current assets and other long-term assets	9 Months Ended
	Sep. 30, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other current assets and other long-term assets	Other current assets and other long-term assets Other current assets consisted of the following (in thousands): September 30, December 31, 2019 2018 Prepaid expenses $ 6,230 $ 1,261 Deposits and other receivables 2,247 1,841 Interest receivable 1,618 768 Right-of-use asset 341 — $ 10,436 $ 3,870 The other long-term assets balance as of September 30, 2019 consisted of $5.2 million in deposits paid in conjunction with the Company's research and development activities, and $0.3 million for a security deposit in connection with the lease of the Company's future corporate headquarters. As of December 31, 2018 , the other long-term assets balance consisted of $1.3 million in deposits paid in conjunction with the Company's research and development activities.

Property and equipment, net

Property and equipment, net	9 Months Ended
	Sep. 30, 2019
Property, Plant and Equipment [Abstract]
Property and equipment, net	Property and equipment, net Property and equipment consisted of the following (in thousands): September 30, December 31, 2019 2018 Computer equipment $ 201 $ 201 Office and other equipment 329 260 Laboratory equipment 880 729 Leasehold improvements 63 63 Gross property and equipment 1,473 1,253 Less: Accumulated depreciation (937 ) (780 ) Property and equipment, net $ 536 $ 473 The Company incurred immaterial depreciation expense for both the three months ended September 30, 2019 and 2018 , and $0.2 million and $0.1 million for the nine months ended September 30, 2019 and 2018 , respectively.

Accounts payable, accrued liabi

Accounts payable, accrued liabilities and long-term liabilities	9 Months Ended
	Sep. 30, 2019
Payables and Accruals [Abstract]
Accounts payable, accrued liabilities and long-term liabilities	Accounts payable, accrued liabilities and long-term liabilities Accounts payable and accrued liabilities consisted of the following (in thousands): September 30, December 31, 2019 2018 Accounts payable $ 12,568 $ 8,531 Accrued clinical expense 14,687 10,154 Accrued development and other expense 2,613 1,243 Accrued compensation and benefits 4,821 5,847 $ 34,689 $ 25,775 The long-term liabilities balance of $0.9 million as of September 30, 2019 consisted primarily of clinical trial-related liabilities. As of December 31, 2018 , the long-term liabilities balance of $0.7 million consisted of $0.1 million in deferred revenue and $0.6 million

BeiGene Agreement

BeiGene Agreement	9 Months Ended
	Sep. 30, 2019
Research and Development [Abstract]
BeiGene Agreement	BeiGene Agreement Terms of Agreement On January 7, 2018, the Company and BeiGene Ltd, ("BeiGene") entered into a Collaboration and License Agreement (the “Agreement”), pursuant to which the Company and BeiGene agreed to collaboratively develop sitravatinib in Asia (excluding Japan and certain other countries), Australia and New Zealand (the “Licensed Territory”). Under the Agreement, the Company granted BeiGene an exclusive license to develop, manufacture and commercialize sitravatinib in the Licensed Territory, with Mirati retaining exclusive rights for the development, manufacture and commercialization of sitravatinib outside the Licensed Territory. As consideration for the rights granted to BeiGene under the Agreement, BeiGene paid the Company a non-refundable, non-creditable up-front fee of $10.0 million . BeiGene is also required to make milestone payments to the Company of up to an aggregate of $123.0 million upon the first achievement of specified clinical, regulatory and sales milestones. The Agreement additionally provides that BeiGene is obligated to pay to the Company royalties at tiered percentage rates ranging from mid-single digits to twenty percent on annual net sales of licensed products in the Licensed Territory, subject to reduction under specified circumstances. The Agreement also provides that the Company will supply BeiGene with sitravatinib for use in BeiGene’s development activities in the Licensed Territory. The Agreement will terminate upon the expiration of the last royalty term for the licensed products, which is the latest of (i) the date of expiration of the last valid patent claim related to the licensed products under the Agreement, (ii) 10 years after the first commercial sale of a licensed product and (iii) the expiration of any regulatory exclusivity as to a licensed product. BeiGene may terminate the Agreement at any time by providing 60 days prior written notice to the Company. Either party may terminate the Agreement upon a material breach by the other party that remains uncured following 60 days after the date of written notice of such breach or upon certain bankruptcy events. In addition, the Company may terminate the Agreement upon written notice to BeiGene under specified circumstances if BeiGene challenges the licensed patent rights. Revenue Recognition The Company evaluated the Agreement under Topic 606. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under the Agreement, the Company performed the following steps: (i) identified the promised goods or services in the contract; (ii) determined whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measured the transaction price, including any constraints on variable consideration; (iv) allocated the transaction price to the performance obligations; and (v) recognized revenue when (or as) the Company satisfied each performance obligation. The Company determined the transaction price is equal to the up-front fee of $10.0 million . The transaction price was allocated to the performance obligations on the basis of the relative stand-alone selling price estimated for each performance obligation. In estimating the stand-alone selling price for each performance obligation, the Company developed assumptions that require judgment and included forecasted revenues, expected development timelines, discount rates, probabilities of technical and regulatory success and costs for manufacturing clinical supplies. As such, of the up-front fee, the Company allocated $9.5 million to the license to the Company's intellectual property, bundled with the associated know-how, and $0.5 million to the initial obligation to supply sitravatinib for clinical development in the Licensed Territory. Licenses of Intellectual Property. The license to the Company’s intellectual property, bundled with the associated know-how, represents a distinct performance obligation. The license and associated know-how was transferred to BeiGene during the three months ended March 31, 2018, therefore during 2018 the Company recognized the full revenue amount of $9.5 million related to this performance obligation as license and collaboration revenues in its condensed consolidated statements of operations and comprehensive loss; no revenue related to this performance obligation was recorded during the three or nine months ended September 30, 2019 . Manufacturing Supply Services. The Company's initial obligation to supply sitravatinib for clinical development in the Licensed Territory represents a distinct performance obligation. The Company recognizes revenue when BeiGene obtains control of the goods, upon delivery, over the period of the obligation, which began in late 2018 and will continue into 2020. The Company recognized $1.0 million as license and collaboration revenues for this performance obligation for the three months ended September 30, 2019 , primarily consisting of cost-sharing payments due from BeiGene. The Company recognized $2.8 million as license and collaboration revenues for this performance obligation for the nine months ended September 30, 2019 , of which $2.6 million relates to cost-sharing payments due from BeiGene and $0.2 million relates to recognition from the deferred revenue balance. No revenue related to the manufacturing supply services obligation was recognized during the three and nine months ended September 30, 2018 . At September 30, 2019 , $1.0 million of cost-sharing receivable from BeiGene was recorded in other current assets on the condensed consolidated balance sheets. Milestone Payments. The Company is entitled to development milestones under the agreement. The next clinical development milestone is for BeiGene initiating the first pivotal clinical trial in the Licensed Territory upon which the Company will be paid a $5.0 million milestone payment. The Company is also entitled to certain regulatory milestone payments which are paid upon receipt of regulatory approvals within the Licensed Territory. No milestone payments were earned during the three and nine months ended September 30, 2019 or 2018 . The Company evaluated whether the remaining milestones are considered probable of being reached and determined that the remaining potential milestone payments are probable of significant revenue reversal as their achievement is highly dependent on factors outside the Company's control. Therefore, these payments have been fully constrained and are not included in the transaction price. At the end of each subsequent reporting period, the Company will re-evaluate the probability of achievement of each milestone and any related constraint, and if necessary, adjust its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect the reported amount of license and collaboration revenues in the period of adjustment. Royalties. As the license is deemed to be the predominant item to which sales-based royalties relate, the Company will recognize revenue when the related sales occur. No royalty revenue was recognized during the three and nine months ended September 30, 2019 or 2018 . The following table presents a summary of the activity in the Company's contract liabilities during the nine months ended September 30, 2019 (in thousands): Opening balance, January 1, 2019 $ (481 ) Revenue from performance obligations satisfied during reporting period 174 Closing balance, September 30, 2019 $ (307 ) The closing balance represents deferred revenue and is classified within current liabilities at September 30, 2019 .

Warrants

Warrants	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Warrants	Warrants As of September 30, 2019 , the following warrants for common stock were issued and outstanding: Issue date Expiration date Exercise price Number of warrants outstanding January 11, 2017 None $ 0.001 5,133,230 November 20, 2017 None $ 0.001 4,137,999 June 11, 2018 None $ 0.001 421,650 9,692,879 During the three months ended September 30, 2019 , 725,008 warrants for shares of the Company's common stock were exercised via cashless exercise, resulting in the issuance of 725,000 shares of common stock. During the nine months ended September 30, 2019 , 2,125,033 warrants for shares of the Company's common stock were exercised via cashless exercise, resulting in the issuance of 2,125,000 shares of common stock. During the three and nine months ended September 30, 2018 , no Sale of Common Stock In June 2019, the Company sold 2,415,000 shares of its common stock at a public offering price of $97.00 per share. After deducting underwriter discounts, commissions and offering expenses, the Company received net cash proceeds from the transaction of $219.9 million . In January 2019, the Company sold 1,854,838 shares of its common stock at a public offering price of $62.00 per share. After deducting underwriter discounts, commissions and offering expenses, the Company received net cash proceeds from the transaction of $107.9 million . In June 2018, the Company sold 3,162,500 shares of its common stock at a public offering price of $38.85 per share and sold warrants to purchase up to 421,650 shares of its common stock at a public offering price of $38.849 per warrant. After deducting underwriter discounts and offering expenses, the Company received net proceeds from the transaction of $130.7 million . The public offering price for the warrants was equal to the public offering price of the common stock, less the $0.001 per share exercise price of each warrant. The warrants were recorded as a component of stockholders’ equity within additional paid-in capital. Per their terms, the outstanding warrants to purchase shares of common stock may not be exercised if certain holders' ownership of the Company’s common stock would exceed 9.99% for certain holders or 4.99% for other holders, following such exercise. Share-based Compensation Total share-based compensation expense by statement of operations and comprehensive loss classification is presented below (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Research and development expense $ 8,648 $ 1,849 $ 20,416 $ 5,113 General and administrative expense 6,458 2,209 18,410 6,479 $ 15,106 $ 4,058 $ 38,826 $ 11,592 During the three and nine months ended September 30, 2019 , 91,257 and 424,144 shares were issued pursuant to stock option exercises, generating net proceeds of $1.1 million and $5.4 million , respectively. During the three and nine months ended September 30, 2018 , 202,601 and 716,409 shares were issued pursuant to stock option exercises, generating net proceeds of $2.2 million and $9.5 million , respectively. Disgorgement Proceeds In January 2019, the Company received a payment of $1.1 million

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies On June 24, 2014, the Company entered into a lease agreement for completed office and laboratory space located in San Diego, California. The office space under the lease is the Company's corporate headquarters. The lease commenced in two phases (in July 2014 and March 2015) at a combined total initial monthly rent of $24,100 per month. The leased property is subject to a 3% annual rent increase following availability. In addition to such base monthly rent, the Company is obligated to pay certain customary amounts for its share of operating expenses and facility amenities. The original lease provided for expiration on January 31, 2018. On March 23, 2017, the Company entered into a First Amendment to Lease Agreement to amend the original lease agreement and to extend the term of the original lease for one year through January 31, 2019. On April 5, 2018, the Company entered into a Second Amendment to Lease Agreement to extend the lease term through January 31, 2020. On August 2, 2018, the Company entered into a Third Amendment to Lease Agreement to expand the size of the existing space for an additional base rent of $4,000 per month. Subsequently, on August 22, 2019, the Company entered into a Fourth Amendment to Lease Agreement to extend the lease term to approximately October 1, 2020, and to expand the size of the existing space for no additional base rent. All other terms and covenants from the original lease agreement remain unchanged. The Company's building lease is considered to be an operating lease. The lease agreement indicates the interest rate applicable to the lease is 12% , therefore the Company used a discount rate of 12% to calculate the value of its lease obligations. The Company re-measured the operating right-of-use asset and operating lease liability due to the Fourth Amendment to Lease Agreement. As of September 30, 2019 , the condensed consolidated balance sheet includes a $0.3 million operating right-of-use asset within other current assets, and a $0.3 million operating lease liability in deferred revenue and other current liabilities. For the three and nine months ended September 30, 2019 , the Company recorded $0.1 million and $0.3 million in operating lease cost, respectively, and the building lease has a remaining lease term of approximately one year from September 30, 2019 . As of September 30, 2019 , remaining lease payments on an undiscounted basis are $0.1 million for 2019 and $0.3 million for 2020. On August 22, 2019, the Company entered into a new lease agreement for office and laboratory space located in San Diego, California, for the Company's future corporate headquarters. The commencement date of this lease is expected to be September 21, 2020 and will expire October 1, 2030, unless terminated earlier. The base rent for the Company under this lease will be approximately $3.8 million for the first year of the lease, which amount will increase by 3% per year over the lease term. As of September 30, 2019 , the Company had not taken control of the space and the lease term had not commenced. Accordingly, no

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2019
Share-based Payment Arrangement [Abstract]
Stockholders' Equity	Warrants As of September 30, 2019 , the following warrants for common stock were issued and outstanding: Issue date Expiration date Exercise price Number of warrants outstanding January 11, 2017 None $ 0.001 5,133,230 November 20, 2017 None $ 0.001 4,137,999 June 11, 2018 None $ 0.001 421,650 9,692,879 During the three months ended September 30, 2019 , 725,008 warrants for shares of the Company's common stock were exercised via cashless exercise, resulting in the issuance of 725,000 shares of common stock. During the nine months ended September 30, 2019 , 2,125,033 warrants for shares of the Company's common stock were exercised via cashless exercise, resulting in the issuance of 2,125,000 shares of common stock. During the three and nine months ended September 30, 2018 , no Sale of Common Stock In June 2019, the Company sold 2,415,000 shares of its common stock at a public offering price of $97.00 per share. After deducting underwriter discounts, commissions and offering expenses, the Company received net cash proceeds from the transaction of $219.9 million . In January 2019, the Company sold 1,854,838 shares of its common stock at a public offering price of $62.00 per share. After deducting underwriter discounts, commissions and offering expenses, the Company received net cash proceeds from the transaction of $107.9 million . In June 2018, the Company sold 3,162,500 shares of its common stock at a public offering price of $38.85 per share and sold warrants to purchase up to 421,650 shares of its common stock at a public offering price of $38.849 per warrant. After deducting underwriter discounts and offering expenses, the Company received net proceeds from the transaction of $130.7 million . The public offering price for the warrants was equal to the public offering price of the common stock, less the $0.001 per share exercise price of each warrant. The warrants were recorded as a component of stockholders’ equity within additional paid-in capital. Per their terms, the outstanding warrants to purchase shares of common stock may not be exercised if certain holders' ownership of the Company’s common stock would exceed 9.99% for certain holders or 4.99% for other holders, following such exercise. Share-based Compensation Total share-based compensation expense by statement of operations and comprehensive loss classification is presented below (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Research and development expense $ 8,648 $ 1,849 $ 20,416 $ 5,113 General and administrative expense 6,458 2,209 18,410 6,479 $ 15,106 $ 4,058 $ 38,826 $ 11,592 During the three and nine months ended September 30, 2019 , 91,257 and 424,144 shares were issued pursuant to stock option exercises, generating net proceeds of $1.1 million and $5.4 million , respectively. During the three and nine months ended September 30, 2018 , 202,601 and 716,409 shares were issued pursuant to stock option exercises, generating net proceeds of $2.2 million and $9.5 million , respectively. Disgorgement Proceeds In January 2019, the Company received a payment of $1.1 million

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The unaudited condensed consolidated financial statements contained in this Quarterly Report on Form 10-Q have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission ("SEC") and, therefore, certain information and disclosures normally included in annual financial statements prepared in accordance with accounting principles generally accepted in the United States of America ("U.S. GAAP") have been omitted. In the opinion of management, the information reflects all adjustments necessary to make the results of operations for the interim periods a fair statement of such operations. All such adjustments are of a normal recurring nature. Interim results are not necessarily indicative of results for the full year. The condensed consolidated balance sheet at December 31, 2018 has been derived from the audited consolidated financial statements at that date, but does not include all information and footnotes required by U.S. GAAP for complete financial statements. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements included in the Company's Annual Report on Form 10-K for the fiscal year ended December 31, 2018 .
Use of Estimates	Use of Estimates The preparation of the Company's unaudited condensed consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. Reported amounts and note disclosures reflect the overall economic conditions that are most likely to occur and anticipated measures management intends to take. Actual results could differ materially from those estimates. Estimates and assumptions are reviewed quarterly. Any revisions to accounting estimates are recognized in the period in which the estimates are revised and in any future periods affected.
Cash and Cash Equivalents	Cash and cash equivalents consist of cash and highly liquid securities with original maturities at the date of acquisition of ninety days or less.
Short-term Investments	Investments with an original maturity of more than ninety days
Concentration of Credit Risk	Concentration of Credit Risk The Company invests its excess cash in accordance with its investment policy. The Company's investments are comprised primarily of commercial paper and debt instruments of financial institutions, corporations, U.S. government-sponsored agencies and the U.S. Treasury. The Company mitigates credit risk by maintaining a diversified portfolio and limiting the amount of investment exposure as to institution, maturity and investment type. Financial instruments that potentially subject the Company to significant credit risk consist principally of cash equivalents and short-term investments.
Revenue Recognition	Revenue Recognition The Company recognizes revenue in connection with a collaboration and license agreement in accordance with the guidance of Revenue From Contracts With Customers, Accounting Standards Codification ("ASC") Topic 606 ("Topic 606"). Under Topic 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements the Company determines are within the scope of Topic 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. See Note 9 for a complete discussion of the revenue recognition for the Company’s collaboration and license agreement.
Net loss per share	Net loss per share
New Accounting Pronouncements	Recently Adopted Accounting Pronouncements In February 2016, the FASB issued Accounting Standards Update ("ASU") 2016-02, Leases (Topic 842) in order to increase transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet for those leases classified as operating leases under previous GAAP. ASU 2016-02 requires a lessee to recognize a liability for lease payments (the lease liability) and a right-of-use asset (representing its right to use the underlying asset for the lease term) on the balance sheet. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018 (including interim periods within those periods) using a modified retrospective approach. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements , which provides entities an optional transition method to apply the new guidance as of the adoption date, rather than as of the earliest period presented. In transition, entities may also elect a package of practical expedients that must be applied in its entirety to all leases commencing before the effective date, unless the lease was modified, to not reassess (a) the existence of a lease, (b) lease classification or (c) determination of initial direct costs, which effectively allows entities to carryforward accounting conclusions under previous U.S. GAAP. The Company adopted ASU 2016-02, using the optional transition method and electing the package of practical expedients described above on January 1, 2019. Due to the adoption, the Company recognized a new lease liability on the Company's consolidated balance sheet for its operating lease of office and lab space of $367,000 on January 1, 2019, with a corresponding right-of-use asset of the same amount based on the present value of the remaining minimum rental payments. See Note 11 for further discussion. In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260); Distinguishing Liabilities from Equity (Topic 480); Derivatives and Hedging (Topic 815): (Part I) Accounting for Certain Financial Instruments with Down Round Features, (Part II) Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Non-controlling Interests with a Scope Exception . This ASU allows companies to exclude a down round feature when determining whether a financial instrument (or embedded conversion feature) is considered indexed to the entity’s own stock. As a result, financial instruments (or embedded conversion features) with down round features may no longer be required to be classified as liabilities. A company will recognize the value of a down round feature only when it is triggered and the strike price has been adjusted downward. For equity-classified freestanding financial instruments, such as warrants, an entity will treat the value of the effect of the down round, when triggered, as a dividend and a reduction of income available to common shareholders in computing basic earnings per share. For convertible instruments with embedded conversion features containing down round provisions, entities will recognize the value of the down round as a beneficial conversion discount to be amortized to earnings. Effective January 1, 2019, the Company adopted the provisions of ASU 2017-11. The adoption did not have a material impact on the Company's consolidated financial statements or related financial statement disclosures. On August 17, 2018, the SEC adopted amendments to certain disclosure requirements in Securities Act Release No. 33-10532, Disclosure Update and Simplification. Among the amendments is the requirement to present the changes in stockholders’ equity in the interim financial statements (either in a separate statement or footnote) in quarterly reports on Form 10-Q. The amendments are effective for all filings made on or after November 5, 2018. In light of the timing of effectiveness of the amendments and proximity of effectiveness to the filing date for most filers’ quarterly reports, the SEC indicated it would not object if the filer’s first presentation of the changes in stockholders’ equity is included in its Form 10-Q for the quarter that begins after the effective date of the amendments. The Company began including a condensed consolidated statement of changes in stockholders' equity in the Company's consolidated financial statements for the three months ended March 31, 2019 and 2018, and has included a condensed consolidated statement of changes in stockholders' equity in the Company's consolidated financial statements for the nine months ended September 30, 2019 and 2018 herein. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 . The amendments provide guidance on whether certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606. It also specifically (i) addresses when the participant should be considered a customer in the content of a unit of account, (ii) adds unit-of-account guidance in ASC 808 to align with guidance with ASC 606, and (iii) precludes presenting revenue from a collaborative arrangement together with revenue recognized under ASC 606 if the collaborative arrangement participant is not a customer. The guidance in ASU 2018-18 is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. Early adoption is permitted and should be applied retrospectively. The Company elected to early adopt this guidance effective January 1, 2019. The adoption had no impact on the Company's consolidated financial statements. Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments , which changes the impairment model for most financial assets and certain other instruments. For trade receivables and other instruments, entities will be required to use a new forward-looking expected loss model that generally will result in the earlier recognition of allowances for losses. For available-for-sale debt securities with unrealized losses, the losses will be recognized as allowances rather than as reductions in the amortized cost of the securities. This guidance is effective for annual reporting periods beginning after December 15, 2019, including interim periods within those years, with early adoption permitted only as of annual reporting periods beginning after December 15, 2018. The Company is currently evaluating the impact of the adoption of this guidance on the Company’s consolidated financial statements. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement . The new guidance modifies the disclosure requirements on fair value measurements in Topic 820. The amendments in ASU 2018-13 are effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company does not anticipate that the adoption of ASU 2018-13 will have a material impact on the Company's consolidated financial statements or related financial statement disclosures.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Schedule of Potentially Dilutive Securities not included in the Calculation of Diluted Net Loss per Share	The following table presents the weighted-average number of common share equivalents, calculated using the treasury stock method, not included in the calculation of diluted net loss per share due to the anti-dilutive effect of the securities: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Common stock options 2,487,135 2,215,086 2,398,467 1,835,879 Common stock warrants 9,826,743 11,817,700 10,412,385 11,568,961 Total 12,313,878 14,032,786 12,810,852 13,404,840

Short-term Investments (Tables)

Short-term Investments (Tables)	9 Months Ended
	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Schedule of Available-for-sale Securities Reconciliation	The following tables summarize the Company's short-term investments (dollars in thousands): As of September 30, 2019 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 2 years or less $ 180,580 $ 271 $ (3 ) $ 180,848 Commercial paper 1 year or less 110,918 67 — 110,985 U.S. Agency bonds 2 years or less 37,500 21 — 37,521 U.S. Treasury bills 1 year or less 32,943 21 (10 ) 32,954 $ 361,941 $ 380 $ (13 ) $ 362,308 As of December 31, 2018 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 1 year or less $ 111,933 $ 26 $ (43 ) $ 111,916 Commercial paper 1 year or less 74,433 — (24 ) 74,409 U.S. Treasury bills 1 year or less 3,771 — — 3,771 $ 190,137 $ 26 $ (67 ) $ 190,096

Fair value measurements (Tables

Fair value measurements (Tables)	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following tables summarize the assets measured at fair value on a recurring basis (in thousands): September 30, 2019 Total Level 1 Level 2 Assets Cash and cash equivalents: Cash $ 3,078 $ 3,078 $ — Money market funds 88,826 88,826 — Total cash and cash equivalents 91,904 91,904 — Short-term investments: U.S. Treasury bills 32,954 32,954 — Corporate debt securities 180,848 — 180,848 Commercial paper 110,985 — 110,985 U.S. Agency bonds 37,521 — 37,521 Total short-term investments 362,308 32,954 329,354 Total $ 454,212 $ 124,858 $ 329,354 December 31, 2018 Total Level 1 Level 2 Assets Cash and cash equivalents: Cash $ 3,731 $ 3,731 $ — Money market funds 28,963 28,963 — Total cash and cash equivalents 32,694 32,694 — Short-term investments: U.S. Treasury bills 3,771 3,771 — Corporate debt securities 111,916 — 111,916 Commercial paper 74,409 — 74,409 Total short-term investments 190,096 3,771 186,325 Total $ 222,790 $ 36,465 $ 186,325

Other current assets and othe_2

Other current assets and other long-term assets (Tables)	9 Months Ended
	Sep. 30, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Other Current Assets	Other current assets consisted of the following (in thousands): September 30, December 31, 2019 2018 Prepaid expenses $ 6,230 $ 1,261 Deposits and other receivables 2,247 1,841 Interest receivable 1,618 768 Right-of-use asset 341 — $ 10,436 $ 3,870

Property and equipment, net (Ta

Property and equipment, net (Tables)	9 Months Ended
	Sep. 30, 2019
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consisted of the following (in thousands): September 30, December 31, 2019 2018 Computer equipment $ 201 $ 201 Office and other equipment 329 260 Laboratory equipment 880 729 Leasehold improvements 63 63 Gross property and equipment 1,473 1,253 Less: Accumulated depreciation (937 ) (780 ) Property and equipment, net $ 536 $ 473

Accounts payable, accrued lia_2

Accounts payable, accrued liabilities and long-term liabilities (Tables)	9 Months Ended
	Sep. 30, 2019
Payables and Accruals [Abstract]
Schedule of Accounts Payable and Accrued Liabilities	Accounts payable and accrued liabilities consisted of the following (in thousands): September 30, December 31, 2019 2018 Accounts payable $ 12,568 $ 8,531 Accrued clinical expense 14,687 10,154 Accrued development and other expense 2,613 1,243 Accrued compensation and benefits 4,821 5,847 $ 34,689 $ 25,775

BeiGene Agreement (Tables)

BeiGene Agreement (Tables)	9 Months Ended
	Sep. 30, 2019
Research and Development [Abstract]
Schedule of Activity in Contract Liabilities	The following table presents a summary of the activity in the Company's contract liabilities during the nine months ended September 30, 2019 (in thousands): Opening balance, January 1, 2019 $ (481 ) Revenue from performance obligations satisfied during reporting period 174 Closing balance, September 30, 2019 $ (307 )

Warrants (Tables)

Warrants (Tables)	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Schedule of Warrants Issued and Outstanding	As of September 30, 2019 , the following warrants for common stock were issued and outstanding: Issue date Expiration date Exercise price Number of warrants outstanding January 11, 2017 None $ 0.001 5,133,230 November 20, 2017 None $ 0.001 4,137,999 June 11, 2018 None $ 0.001 421,650 9,692,879

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2019
Share-based Payment Arrangement [Abstract]
Schedule of Employee Service Share-based Compensation Allocation	Total share-based compensation expense by statement of operations and comprehensive loss classification is presented below (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Research and development expense $ 8,648 $ 1,849 $ 20,416 $ 5,113 General and administrative expense 6,458 2,209 18,410 6,479 $ 15,106 $ 4,058 $ 38,826 $ 11,592

Description of Business - Narra

Description of Business - Narrative (Details)	9 Months Ended
	Sep. 30, 2019segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narrative (Details)	9 Months Ended
	Sep. 30, 2019
Marketable Securities
Minimum original maturity period of marketable securities	90 days

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	12,313,878	14,032,786	12,810,852	13,404,840
Common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	2,487,135	2,215,086	2,398,467	1,835,879
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	9,826,743	11,817,700	10,412,385	11,568,961

Recently Adopted and Recently_2

Recently Adopted and Recently Issued Accounting Pronouncements - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use asset	$ 341		$ 0
Accounting Standards Update 2016-06
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liability		$ 367
Right-of-use asset		$ 367

Short-term Investments - Summar

Short-term Investments - Summary (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 361,941	$ 190,137
Gross unrealized gains	380	26
Gross unrealized losses	(13)	(67)
Estimated fair value	$ 362,308	$ 190,096
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Maturity	2 years	1 year
Amortized cost	$ 180,580	$ 111,933
Gross unrealized gains	271	26
Gross unrealized losses	(3)	(43)
Estimated fair value	$ 180,848	$ 111,916
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Maturity	1 year	1 year
Amortized cost	$ 110,918	$ 74,433
Gross unrealized gains	67	0
Gross unrealized losses	0	(24)
Estimated fair value	$ 110,985	$ 74,409
U.S. Agency bonds
Debt Securities, Available-for-sale [Line Items]
Maturity	2 years
Amortized cost	$ 37,500
Gross unrealized gains	21
Gross unrealized losses	0
Estimated fair value	$ 37,521
U.S. Treasury bills
Debt Securities, Available-for-sale [Line Items]
Maturity	1 year	1 year
Amortized cost	$ 32,943	$ 3,771
Gross unrealized gains	21	0
Gross unrealized losses	(10)	0
Estimated fair value	$ 32,954	$ 3,771

Fair value measurements - Summa

Fair value measurements - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	$ 91,904	$ 32,694
Total short-term investments	362,308	190,096
Total	454,212	222,790
U.S. Treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	32,954	3,771
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	180,848	111,916
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	110,985	74,409
U.S. Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	37,521
Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	3,078	3,731
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	88,826	28,963
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	91,904	32,694
Total short-term investments	32,954	3,771
Total	124,858	36,465
Level 1 | U.S. Treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	32,954	3,771
Level 1 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Level 1 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Level 1 | U.S. Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0
Level 1 | Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	3,078	3,731
Level 1 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	88,826	28,963
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Total short-term investments	329,354	186,325
Total	329,354	186,325
Level 2 | U.S. Treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Level 2 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	180,848	111,916
Level 2 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	110,985	74,409
Level 2 | U.S. Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	37,521
Level 2 | Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Level 2 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	$ 0	$ 0

Other current assets and othe_3

Other current assets and other long-term assets - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 6,230	$ 1,261
Deposits and other receivables	2,247	1,841
Interest receivable	1,618	768
Right-of-use asset	341	0
Other current assets	10,436	3,870
Deposits paid for research and development	5,200	$ 1,300
Security deposit for lease	$ 300

Property and equipment, net - S

Property and equipment, net - Summary (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Gross property and equipment	$ 1,473		$ 1,253
Less: Accumulated depreciation	(937)		(780)
Property and equipment, net	536		473
Depreciation	156	$ 131
Computer equipment
Property, Plant and Equipment [Line Items]
Gross property and equipment	201		201
Office and other equipment
Property, Plant and Equipment [Line Items]
Gross property and equipment	329		260
Laboratory equipment
Property, Plant and Equipment [Line Items]
Gross property and equipment	880		729
Leasehold improvements
Property, Plant and Equipment [Line Items]
Gross property and equipment	$ 63		$ 63

Accounts payable, accrued lia_3

Accounts payable, accrued liabilities and long-term liabilities - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Accounts payable	$ 12,568	$ 8,531
Accrued clinical expense	14,687	10,154
Accrued development and other expense	2,613	1,243
Accrued compensation and benefits	4,821	5,847
Total accounts payable and accrued liabilities	34,689	25,775
Long-term liabilities	$ 873	732
Deferred revenue		100
Other liabilities		$ 600

BeiGene Agreement - Narrative (

BeiGene Agreement - Narrative (Details) - Collaboration and License Agreement - USD ($)	Jan. 07, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Up-front fee received	$ 10,000,000
Termination of contract, period after first commercial sale of product	10 years
Period required for notice of termination of contract	60 days
Revenue from performance obligations satisfied during reporting period				$ 174,000
Revenue from performance obligation expected to be earned	$ 123,000,000
Licenses of Intellectual Property
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation earned		$ 0		0		$ 9,500,000
Manufacturing Supply Services
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Payments received in advance		(1,000,000)	$ 0	(2,800,000)	$ 0
Revenue from performance obligations satisfied during reporting period				200,000
Revenue from performance obligation earned				2,600,000		$ 500,000
Cost-sharing receivable				1,000,000
Milestone Payments
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation expected to be earned		5,000,000		5,000,000
Milestone payments earned		0	0	0	0
Royalties
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue		$ 0	$ 0	$ 0	$ 0

BeiGene Agreement - Activity in

BeiGene Agreement - Activity in Contract Liabilities (Details) - Collaboration and License Agreement $ in Thousands	9 Months Ended
	Sep. 30, 2019USD ($)
Movement in Deferred Revenue [Roll Forward]
Opening balance at beginning of period	$ (481)
Revenue from performance obligations satisfied during reporting period	174
Closing balance at end of period	$ (307)

Warrants - Summary (Details)

Warrants - Summary (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2018
Class of Warrant or Right [Line Items]
Exercise price of warrants (USD per share)					$ 0.001
Number of warrants outstanding (shares)	9,692,879		9,692,879
Warrants exercised via cashless exercises (shares)	725,008	0	2,125,033	0
Common stock issued from exercise of warrants (shares)	725,000		2,125,000
January 11, 2017 Warrants
Class of Warrant or Right [Line Items]
Exercise price of warrants (USD per share)	$ 0.001		$ 0.001
Number of warrants outstanding (shares)	5,133,230		5,133,230
November 20, 2017 Warrants
Class of Warrant or Right [Line Items]
Exercise price of warrants (USD per share)	$ 0.001		$ 0.001
Number of warrants outstanding (shares)	4,137,999		4,137,999
June 11, 2018 Warrants
Class of Warrant or Right [Line Items]
Exercise price of warrants (USD per share)	$ 0.001		$ 0.001
Number of warrants outstanding (shares)	421,650		421,650

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Right-of-use asset	$ 341,000	$ 341,000	$ 0
Current Headquarters
Lessee, Lease, Description [Line Items]
Minimum monthly rental expense		$ 4,000
Discount rate (as a percent)	12.00%	12.00%
Right-of-use asset	$ 300,000	$ 300,000
Operating lease liability	300,000	300,000
Operating lease cost	100,000	$ 300,000
Remaining lease term		1 year
Remaining lease payments for remainder of fiscal year	100,000	$ 100,000
Remaining lease payments in year two	300,000	300,000
Future Headquarters
Lessee, Lease, Description [Line Items]
Right-of-use asset	0	0
Operating lease liability	$ 0	0
Building | Current Headquarters
Lessee, Lease, Description [Line Items]
Minimum monthly rental expense		$ 24,100
Annual rent increase (as a percent)	3.00%	3.00%
Building | Future Headquarters
Lessee, Lease, Description [Line Items]
Minimum monthly rental expense		$ 3,800,000
Annual rent increase (as a percent)	3.00%	3.00%

Stockholders' Equity - Narrativ

Stockholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jan. 31, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued in transaction (shares)	2,415,000	1,854,838	3,162,500
Sale price of common stock (USD per share)	$ 97	$ 62	$ 38.85
Proceeds from sale of stock	$ 219,900	$ 107,900	$ 130,700
Exercise price of warrants (USD per share)			$ 0.001
Stock issued pursuant to stock option exercises (shares)				91,257	202,601	424,144	716,409
Proceeds from stock options exercised				$ 1,100	$ 2,200	$ 5,400	$ 9,500
Proceeds from disgorgement of stockholders' short-swing profits		$ 1,100				$ 1,050	$ 0
Note Warrant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued in transaction (shares)			421,650
Sale price of common stock (USD per share)			$ 38.849
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proportion of common stock owned (as a percent)							9.99%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proportion of common stock owned (as a percent)							4.99%

Stockholders' Equity - Summary

Stockholders' Equity - Summary (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	$ 15,106	$ 4,058	$ 38,826	$ 11,592
Research and development expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	8,648	1,849	20,416	5,113
General and administrative expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	$ 6,458	$ 2,209	$ 18,410	$ 6,479

Uncategorized Items - mrtx-2019

Label	Element	Value
Restricted Cash	us-gaap_RestrictedCash	$ 320,000
Restricted Cash	us-gaap_RestrictedCash	$ 0