Mirati Therapeutics (MRTX) 10-Q 4 Nov 20 2020 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2020	Nov. 02, 2020
Cover [Abstract]
Entity Central Index Key	0001576263
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
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		50,281,081

Description of Business

Description of Business	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of BusinessMirati 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 business segment, primarily in the United States. The Company's common stock has been listed on the Nasdaq Global Select Market since June 5, 2018, and was previously listed on the Nasdaq Capital Market since July 15, 2013, under the ticker symbol "MRTX."

Recently Adopted and Recently I

Recently Adopted and Recently Issued Accounting Pronouncements	9 Months Ended
	Sep. 30, 2020
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 June 2016, the FASB issued Accounting Standards Update ("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 are required to use a new forward-looking expected loss model that generally results in the earlier recognition of allowances for losses. For available-for-sale debt securities with unrealized losses, the losses are 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. Effective January 1, 2020, the Company adopted the provisions of ASU 2016-13. The adoption did not have a material impact on the Company's consolidated financial statements or related financial statement disclosures. 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. Effective January 1, 2020, the Company adopted the provisions of ASU 2018-13. The adoption did not have a material impact on the Company's consolidated financial statements or related financial statement disclosures. In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes . The update includes removing several exceptions under the existing guidance and includes several simplification updates. The guidance is effective for fiscal years beginning after December 15, 2020 and early adoption is permitted. Effective January 1, 2020, the Company early adopted this updated guidance and it did not have a material impact on the Company's consolidated financial statements or related financial statement disclosures.

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 131,434	$ 46,535
Short-term investments	447,616	368,515
Other current assets	16,341	9,357
Total current assets	595,391	424,407
Property and equipment, net	5,901	1,776
Long-term investment	11,400	0
Other long-term assets	7,159	6,017
Total assets	619,851	432,200
Current liabilities
Accounts payable and accrued liabilities	66,670	48,082
Deferred revenue and other current liabilities	697	824
Total current liabilities	67,367	48,906
Other long-term liabilities	1,541	999
Total liabilities	68,908	49,905
Commitments and contingencies (see Note 11)
Shareholders’ equity
Preferred stock, $0.001 par value; 10,000,000 shares authorized; none issued and outstanding at both September 30, 2020 and December 31, 2019	0	0
Common stock, $0.001 par value; 100,000,000 shares authorized; 44,754,466 and 39,517,329 issued and outstanding at September 30, 2020 and December 31, 2019, respectively	45	40
Additional paid-in capital	1,569,592	1,144,667
Accumulated other comprehensive income	10,457	9,889
Accumulated deficit	(1,029,151)	(772,301)
Total shareholders’ equity	550,943	382,295
Total liabilities and shareholders’ equity	$ 619,851	$ 432,200

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
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)	44,482,308	39,517,329
Common stock outstanding (shares)	44,482,308	39,517,329

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue
License and collaboration revenues	$ 11,424	$ 988	$ 11,690	$ 2,809
Total revenue	11,424	988	11,690	2,809
Operating expenses
Research and development	79,853	47,362	216,644	119,925
General and administrative	20,249	10,685	58,074	30,340
Total operating expenses	100,102	58,047	274,718	150,265
Loss from operations	(88,678)	(57,059)	(263,028)	(147,456)
Other income, net	1,342	2,786	6,178	6,576
Net loss	(87,336)	(54,273)	(256,850)	(140,880)
Unrealized (loss) gain on available-for-sale investments	(827)	103	568	412
Comprehensive loss	$ (88,163)	$ (54,170)	$ (256,282)	$ (140,468)
Basic and diluted net loss per share (USD per share)	$ (1.96)	$ (1.38)	$ (5.87)	$ (3.83)
Weighted average number of shares used in computing net loss per share, basic and diluted (shares)	44,614,226	39,197,213	43,778,607	36,799,173

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) - 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, 2018		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	(140,880)				(140,880)
Issuance of common stock, net of issuance costs (shares)		4,269,838
Issuance of common stock, net of issuance costs	327,810	$ 4	327,806
Share-based compensation expense	38,826		38,826
Issuance of common stock from ESPP (shares)		9,844
Issuance of common stock from ESPP	323		323
Issuance of common stock under equity incentive plans (shares)		424,144
Issuance of common stock under equity incentive plans	$ 5,372		5,372
Net exercise of warrants (shares)	2,125,000	2,125,000
Net exercise of warrants		$ 2	(2)
Proceeds from disgorgement of shareholders' short-swing profits	$ 1,050		1,050
Unrealized gain (loss) on investments	412			412
Balance at end of period (shares) at Sep. 30, 2019		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 Jun. 30, 2019		38,551,426
Balance at beginning of period at Jun. 30, 2019	472,481	$ 39	1,108,306	9,788	(645,652)
Increase (Decrease) in Stockholders' Equity
Net loss	(54,273)				(54,273)
Share-based compensation expense	15,106		15,106
Issuance of common stock from ESPP	0
Issuance of common stock under equity incentive plans (shares)		91,257
Issuance of common stock under equity incentive plans	$ 1,072		1,072
Net exercise of warrants (shares)	725,000	725,000
Unrealized gain (loss) on investments	$ 103			103
Balance at end of period (shares) at Sep. 30, 2019		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 Dec. 31, 2019	39,517,329	39,517,329
Balance at beginning of period at Dec. 31, 2019	$ 382,295	$ 40	1,144,667	9,889	(772,301)
Increase (Decrease) in Stockholders' Equity
Net loss	(256,850)				(256,850)
Issuance of common stock, net of issuance costs (shares)		3,538,462
Issuance of common stock, net of issuance costs	323,977	$ 4	323,973
Share-based compensation expense	64,104		64,104
Issuance of common stock from ESPP (shares)		6,207
Issuance of common stock from ESPP	524		524
Issuance of common stock under equity incentive plans (shares)		1,092,468
Issuance of common stock under equity incentive plans	$ 36,284	$ 1	36,283
Net exercise of warrants (shares)	600,000	600,000
Proceeds from disgorgement of shareholders' short-swing profits	$ 41		41
Unrealized gain (loss) on investments	$ 568			568
Balance at end of period (shares) at Sep. 30, 2020	44,482,308	44,754,466
Balance at end of period at Sep. 30, 2020	$ 550,943	$ 45	1,569,592	10,457	(1,029,151)
Balance at beginning of period (shares) at Jun. 30, 2020		44,482,308
Balance at beginning of period at Jun. 30, 2020	605,004	$ 45	1,535,490	11,284	(941,815)
Increase (Decrease) in Stockholders' Equity
Net loss	(87,336)				(87,336)
Share-based compensation expense	21,751		21,751
Issuance of common stock under equity incentive plans (shares)		272,158
Issuance of common stock under equity incentive plans	12,351		12,351
Unrealized gain (loss) on investments	$ (827)			(827)
Balance at end of period (shares) at Sep. 30, 2020	44,482,308	44,754,466
Balance at end of period at Sep. 30, 2020	$ 550,943	$ 45	$ 1,569,592	$ 10,457	$ (1,029,151)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities:
Net loss	$ (256,850)	$ (140,880)
Non-cash adjustments reconciling net loss to operating cash flows:
Non-cash consideration earned from license agreement	(11,424)	0
Change in fair value of long-term investment	24	0
Depreciation of property and equipment	435	156
Accretion of discount on investments	(877)	(2,818)
Share-based compensation expense	64,104	38,826
Changes in operating assets and liabilities:
Other current assets	(6,985)	(6,566)
Other long-term assets	(843)	(3,873)
Accounts payable, accrued liabilities, deferred revenue and other liabilities	17,306	9,331
Cash flows used in operating activities	(195,110)	(105,824)
Investing activities:
Purchases of short-term investments	(456,608)	(458,115)
Sales and maturities of short-term investments	378,952	289,134
Purchases of property, plant, and equipment	(2,861)	(220)
Cash flows used in investing activities	(80,517)	(169,201)
Financing activities:
Proceeds from issuance of common stock, net of issuance costs	323,977	327,810
Proceeds from issuance of common stock under equity incentive plans	36,283	5,372
Proceeds from disgorgement of shareholders' short-swing profits	41	1,050
Proceeds from stock issuances under employee stock purchase plan	524	323
Cash flows provided by financing activities	360,825	334,555
Increase in cash, cash equivalents and restricted cash	85,198	59,530
Cash, cash equivalents and restricted cash, beginning of period	46,856	32,694
Cash, cash equivalents and restricted cash, end of period	132,054	92,224
Reconciliation of cash, cash equivalents and restricted cash, end of period:
Total cash, cash equivalents and restricted cash	132,054	92,224
Supplemental disclosures of non-cash investing activities:
Allowance utilized for tenant improvements	1,662	0
Fair value of long-term investment earned from license agreement	$ 11,400	$ 0

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
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, 2019 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, 2019. 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 shareholders’ 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 certain collaboration and license agreements 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. Net Loss per Share Basic net loss per common share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, without consideration for common share equivalents as they are anti-dilutive. 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, 2020 2019 2020 2019 Common stock options 2,415,979 2,487,135 2,262,174 2,398,467 Common stock warrants 9,092,807 9,826,743 9,451,913 10,412,385 Total 11,508,786 12,313,878 11,714,087 12,810,852

Investments

Investments	9 Months Ended
	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Investments	Investments The following tables summarize the Company's short-term investments (dollars in thousands): As of September 30, 2020 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 2 years or less $ 159,588 $ 576 $ — $ 160,164 Commercial paper 1 year or less 154,795 296 — 155,091 U.S. Agency bonds 2 years or less 79,120 38 (3) 79,155 U.S. Treasury bills 1 year or less 53,176 30 — 53,206 $ 446,679 $ 940 $ (3) $ 447,616 As of December 31, 2019 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 2 years or less $ 160,065 $ 233 $ (1) $ 160,297 Commercial paper 1 year or less 120,862 74 — 120,936 U.S. Agency bonds 2 years or less 50,745 41 (4) 50,782 U.S. Treasury bills 2 years or less 36,474 27 (1) 36,500 $ 368,146 $ 375 $ (6) $ 368,515 The Company has classified all of its short-term investments 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. As of September 30, 2020, and December 31, 2019, aggregated gross unrealized losses of available-for-sale investments were not material, and accordingly, no allowance for credit losses was recorded as of September 30, 2020.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2020
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, 2 or 3 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, 2020 Total Level 1 Level 2 Level 3 Assets Cash and cash equivalents: Cash $ 18,812 $ 18,812 $ — $ — Money market funds 112,622 112,622 — — Total cash and cash equivalents 131,434 131,434 — — Short-term investments: U.S. Treasury bills 53,206 53,206 — — Corporate debt securities 160,164 — 160,164 — Commercial paper 155,091 — 155,091 — U.S. Agency bonds 79,155 — 79,155 — Total short-term investments 447,616 53,206 394,410 — Long-term investment: ORIC Pharmaceuticals 11,400 — — 11,400 Total $ 590,450 $ 184,640 $ 394,410 $ 11,400 December 31, 2019 Total Level 1 Level 2 Assets Cash and cash equivalents: Cash $ 662 $ 662 $ — Money market funds 45,873 45,873 — Total cash and cash equivalents 46,535 46,535 — Short-term investments: U.S. Treasury bills 36,500 36,500 — Corporate debt securities 160,297 — 160,297 Commercial paper 120,936 — 120,936 U.S. Agency bonds 50,782 — 50,782 Total short-term investments 368,515 36,500 332,015 Total $ 415,050 $ 83,035 $ 332,015 The Company’s investments in Level 1 assets are valued based on publicly available quoted market prices for identical securities as of September 30, 2020 and December 31, 2019. 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. The Level 3 fair value measurement of the Company's long-term investment utilized a combination of the Asian Protective Put Option and Finnerty Put Option fair value techniques with unobservable inputs of 88% volatility and an expected term of 1.3 years to determine the discount for lack of marketability of 22.5%. There were no transfers between fair value measurement levels during the three and nine months ended September 30, 2020 or the year ended December 31, 2019. The following table presents the changes in estimated fair value of the Company's asset measured using significant unobservable inputs (Level 3) (in thousands): September 30, 2020 Balance - January 1, 2020 $ — Additions 11,424 Change in fair value measurement (24) Balance - September 30, 2020 $ 11,400

Other Current Assets and Other

Other Current Assets and Other Long-Term Assets	9 Months Ended
	Sep. 30, 2020
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, 2020 2019 Prepaid expenses $ 8,892 $ 5,672 Deposits and other receivables 5,914 2,119 Interest receivable 1,535 1,566 $ 16,341 $ 9,357 The other long-term assets balance as of September 30, 2020 consisted of $6.0 million in deposits paid in conjunction with the Company's research and development activities, $0.6 million for an operating right-of-use asset for the Company's corporate headquarters, and $0.6 million for a security deposit in connection with the lease of the Company's future corporate headquarters. As of December 31, 2019, the other long-term assets balance consisted of $5.1 million in deposits paid in conjunction with the Company's research and development activities, $0.6 million for an operating right-of-use asset for the Company's corporate headquarters, and $0.3 million for a security deposit in connection with the lease of the Company's future corporate headquarters.

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2020
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, 2020 2019 Computer equipment $ 201 $ 201 Office and other equipment 329 329 Laboratory equipment 4,886 2,212 Leasehold improvements 63 63 Construction-in-progress 1,886 — Gross property and equipment 7,365 2,805 Less: Accumulated depreciation (1,464) (1,029) Property and equipment, net $ 5,901 $ 1,776

Accounts Payable, Accrued Liabi

Accounts Payable, Accrued Liabilities and Long-Term Liabilities	9 Months Ended
	Sep. 30, 2020
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, 2020 2019 Accounts payable $ 15,975 $ 16,367 Accrued clinical expense 35,281 21,290 Accrued development and other expense 7,414 2,510 Accrued compensation and benefits 8,000 7,915 $ 66,670 $ 48,082

License and Collaboration Agree

License and Collaboration Agreements	9 Months Ended
	Sep. 30, 2020
Research and Development [Abstract]
License and Collaboration Agreements	License and Collaboration Agreements BeiGene Agreement Terms of Agreement On January 7, 2018, the Company and BeiGene Ltd, ("BeiGene") entered into a Collaboration and License Agreement (the “BeiGene 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 BeiGene Agreement, the Company granted BeiGene an exclusive license to develop, manufacture and commercialize sitravatinib in the Licensed Territory, with the Company 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 BeiGene 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 BeiGene 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 BeiGene Agreement also provides that the Company will supply BeiGene with sitravatinib for use in BeiGene’s development activities in the Licensed Territory. The BeiGene 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 BeiGene 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 BeiGene Agreement at any time by providing 60 days prior written notice to the Company. Either party may terminate the BeiGene 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 BeiGene Agreement upon written notice to BeiGene under specified circumstances if BeiGene challenges the licensed patent rights. Revenue Recognition The Company evaluated the BeiGene Agreement under Topic 606. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under the BeiGene 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 and nine months ended September 30, 2020 or 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. No revenue related to this performance obligation was recognized for the three months ended September 30, 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 $0.3 million as license and collaboration revenues for this performance obligation for the nine months ended September 30, 2020, 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. Milestone Payments. The Company is entitled to development milestones under the BeiGene 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, 2020 or 2019. The Company evaluated whether the remaining milestones are considered probable of being reached and determined that their achievement is highly dependent on factors outside of 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, 2020 or 2019. The following table presents a summary of the activity in the Company's contract liabilities during the nine months ended September 30, 2020 (in thousands): Opening balance, January 1, 2020 $ (172) Revenue from performance obligations satisfied during reporting period 29 Closing balance, September 30, 2020 $ (143) The closing balance represents deferred revenue and was classified within current liabilities at September 30, 2020. Pfizer Agreement In October 2014, the Company entered into a drug discovery collaboration and option agreement with Array BioPharma, Inc. ("Array," acquired by Pfizer Inc. ("Pfizer") during 2019) whereby Array provided services to facilitate the discovery, optimization and development of small molecule compounds that bind and specifically inhibit KRAS G12C. In June 2017, the two parties entered into a second, separate discovery collaboration and option agreement whereby Array provided services to facilitate the discovery, optimization and development of small molecule compounds that bind and specifically inhibit KRAS G12D. Both agreements established an option mechanism which enabled the Company to elect an exclusive worldwide license under the technology for the development and commercialization of certain products based on such compounds. Under the agreements, following the joint discovery periods which have concluded, the Company executed its options to retain exclusive worldwide licenses to develop, manufacture and commercialize inhibitors of KRAS G12C and KRAS G12D, including but not limited to, MRTX849 (adagrasib is the provisionally filed name for MRTX849) and MRTX1133. Under each agreement, Pfizer is entitled to potential development milestone payments of up to $9.3 million, and tiered sales milestone payments of up to $337.0 million based upon worldwide net sales, and tiered royalties in the high single digits to mid-teens on worldwide net sales of products arising from the collaborations. Under the agreements, the Company has incurred $4.5 million in development milestone payments from inception through September 30, 2020. The royalty term for each agreement shall be payable on a country-by-country and product-by-product basis, and separately will terminate at the later of (i) the date of expiration of the last valid patent claim within the collaboration patent rights or the Pfizer background technology covering such product in the country in which such product is sold at the time of such sale, or (ii) 10 years after the first commercial sale of such product in such country. The Company may terminate each agreement at any time by providing 60 days prior written notice to Pfizer. Either party may terminate each 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. For the three months ended September 30, 2020, the Company incurred expenses under these agreements with Pfizer of $0.3 million relating to a milestone payment for initiation of the first regulatory toxicology study for MRTX1133. For the nine months ended September 30, 2020, the Company incurred expenses under these agreements with Pfizer of $4.8 million, consisting of a $3.0 million milestone payment for initiation of the first Phase 2 trial for MRTX849, a $0.3 million milestone payment for initiation of the first regulatory toxicology study for MRTX1133, and $1.5 million in research and development services. For the three months ended September 30, 2019, the Company incurred expense of $1.5 million, consisting of research and development services. For the nine months ended September 30, 2019, the Company incurred expense of $5.5 million, consisting of a $1.0 million milestone payment for initiation of the first Phase 1 trial for MRTX849, and $4.5 million in research and development services. ORIC Pharmaceuticals Agreement Terms of Agreement On August 3, 2020, the Company entered into a license agreement with ORIC Pharmaceuticals, Inc. ("ORIC") pursuant to which the Company granted to ORIC an exclusive, worldwide license to develop and commercialize the Company's allosteric polycomb repressive complex 2 (PRC2) inhibitors for all indications (the "ORIC License Agreement"). In accordance with the terms of the ORIC License Agreement, in exchange for such license, ORIC issued 588,235 shares of its common stock (the "Shares") to the Company on August 3, 2020. The Shares were issued under a stock issuance agreement entered into between ORIC and the Company, dated August 3, 2020. During the eighteen Unless terminated earlier, the ORIC License Agreement will continue in effect on a country-by-country and licensed product-by-licensed product basis until the later (a) the expiration of the last valid claim of a licensed patent covering such licensed product in such country or (b) ten years after the first commercial sale of such licensed product in such country. Following the expiration of the ORIC License Agreement, ORIC will retain its licenses under the intellectual property the Company licensed to ORIC on a royalty-free basis. The Company and ORIC may each terminate the ORIC License Agreement if the other party materially breaches the terms of such agreement, subject to specified notice and cure provisions, or enters into bankruptcy or insolvency proceedings. The Company may terminate the agreement if ORIC challenges any of the patent rights licensed to ORIC by the Company or if ORIC discontinues development of licensed products for a specified period of time. ORIC also has the right to terminate the ORIC License Agreement without cause by providing prior written notice to the Company. Revenue Recognition The Company accounted for the ORIC License Agreement under Topic 606 and identified the granting of an exclusive, worldwide license to develop and commercialize the Company's allosteric PRC2 inhibitors for all indications as a distinct performance obligation since ORIC can benefit from the license on its own by developing and commercializing the underlying product using its own resources. In determining the transaction price, the Company received the Shares as non-cash consideration. The transaction price was determined by utilizing a Level 3 fair value measurement as further described in Note 5. The Company determined the transaction price was equal to $11.4 million. The Company allocated the entire transaction price to the distinct performance obligation described above, and the license and related know-how was transferred to ORIC during the third quarter of 2020. Therefore, the Company recognized the entire transaction price of $11.4 million as license and collaboration revenues in its condensed consolidated statements of operations and comprehensive loss.

Warrants

Warrants	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Warrants	Warrants As of September 30, 2020, 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 4,533,224 November 20, 2017 None $ 0.001 4,137,999 June 11, 2018 None $ 0.001 421,650 9,092,873 No warrants were exercised during the three months ended September 30, 2020. 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, 2020, 600,006 warrants for shares of the Company's common stock were exercised via cashless exercise, resulting in the issuance of 600,000 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. At the Market Facility On July 2, 2020, the Company entered into a sales agreement pursuant to which the Company may, from time to time, sell shares of the Company's common stock, par value $0.001 per share, having an aggregate offering price of up to $200.0 million. As of September 30, 2020, the Company has not offered or sold any shares of common stock pursuant to this sales agreement. Sale of Common Stock In January 2020, the Company sold 3,538,462 shares of its common stock at a public offering price of $97.50 per share. After deducting underwriter discounts, commissions and offering expenses, the Company received net proceeds from the transaction of $324.0 million. In June 2019, the Company sold 2,415,000 shares of its common stock at a public offering price at $97.00 per share. After deducting underwriter discounts, commissions and offering expenses, the Company received net 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. 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, 2020 2019 2020 2019 Research and development expense $ 12,556 $ 8,648 $ 35,861 $ 20,416 General and administrative expense 9,195 6,458 28,243 18,410 $ 21,751 $ 15,106 $ 64,104 $ 38,826 During the three and nine months ended September 30, 2020, 272,158 and 1,092,468 shares were issued under our equity incentive plans, generating net proceeds of $12.4 million and $36.3 million, respectively. During the three and nine months ended September 30, 2019, 91,257 and 424,144 shares were issued under our equity incentive plans, generating net proceeds of $1.1 million and $5.4 million, respectively. Disgorgement Proceeds

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2020
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. On October 30, 2019, the Company entered into a Fourth Amendment to Lease Agreement to extend the lease term to the first half of 2021, and to expand the size of the existing space for no additional base rent. On March 4, 2020, and July 15, 2020 the Company entered into a Fifth Amendment and Sixth Amendment to Lease Agreement, respectively 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 recorded $0.1 million and $0.1 million in operating lease cost for the three months ended September 30, 2020 and 2019, respectively. The Company recorded $0.2 million and $0.3 million in operating lease cost for the nine months ended September 30, 2020 and 2019, respectively. The building lease has a remaining lease term of under one year from September 30, 2020. As of September 30, 2020, the condensed consolidated balance sheet includes a $0.6 million operating right-of-use asset within other long-term assets, and a $0.6 million operating lease liability in deferred revenue and other current liabilities, and remaining lease payments on an undiscounted basis are $0.1 million for 2020 and $0.1 million for 2021.

Shareholders' Equity

Shareholders' Equity	9 Months Ended
	Sep. 30, 2020
Share-based Payment Arrangement [Abstract]
Shareholders' Equity	Warrants As of September 30, 2020, 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 4,533,224 November 20, 2017 None $ 0.001 4,137,999 June 11, 2018 None $ 0.001 421,650 9,092,873 No warrants were exercised during the three months ended September 30, 2020. 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, 2020, 600,006 warrants for shares of the Company's common stock were exercised via cashless exercise, resulting in the issuance of 600,000 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. At the Market Facility On July 2, 2020, the Company entered into a sales agreement pursuant to which the Company may, from time to time, sell shares of the Company's common stock, par value $0.001 per share, having an aggregate offering price of up to $200.0 million. As of September 30, 2020, the Company has not offered or sold any shares of common stock pursuant to this sales agreement. Sale of Common Stock In January 2020, the Company sold 3,538,462 shares of its common stock at a public offering price of $97.50 per share. After deducting underwriter discounts, commissions and offering expenses, the Company received net proceeds from the transaction of $324.0 million. In June 2019, the Company sold 2,415,000 shares of its common stock at a public offering price at $97.00 per share. After deducting underwriter discounts, commissions and offering expenses, the Company received net 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. 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, 2020 2019 2020 2019 Research and development expense $ 12,556 $ 8,648 $ 35,861 $ 20,416 General and administrative expense 9,195 6,458 28,243 18,410 $ 21,751 $ 15,106 $ 64,104 $ 38,826 During the three and nine months ended September 30, 2020, 272,158 and 1,092,468 shares were issued under our equity incentive plans, generating net proceeds of $12.4 million and $36.3 million, respectively. During the three and nine months ended September 30, 2019, 91,257 and 424,144 shares were issued under our equity incentive plans, generating net proceeds of $1.1 million and $5.4 million, respectively. Disgorgement Proceeds

Subsequent Event

Subsequent Event	9 Months Ended
	Sep. 30, 2020
Subsequent Events [Abstract]
Subsequent Event	Subsequent EventSale of Common Stock In October 2020, the Company sold 4,585,706 shares of its common stock at a public offering price of $202.00 per share. After deducting underwriter discounts, commissions and estimated offering expenses, the Company expects to receive net proceeds from the transaction of approximately $879.7 million

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
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, 2019 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, 2019.
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 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.
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 certain collaboration and license agreements in accordance with the guidance of Revenue From Contracts With Customers,
Net Loss per Share	Net Loss per ShareBasic net loss per common share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, without consideration for common share equivalents as they are anti-dilutive. 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.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In June 2016, the FASB issued Accounting Standards Update ("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 are required to use a new forward-looking expected loss model that generally results in the earlier recognition of allowances for losses. For available-for-sale debt securities with unrealized losses, the losses are 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. Effective January 1, 2020, the Company adopted the provisions of ASU 2016-13. The adoption did not have a material impact on the Company's consolidated financial statements or related financial statement disclosures. 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. Effective January 1, 2020, the Company adopted the provisions of ASU 2018-13. The adoption did not have a material impact on the Company's consolidated financial statements or related financial statement disclosures. In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes . The update includes removing several exceptions under the existing guidance and includes several simplification updates. The guidance is effective for fiscal years beginning after December 15, 2020 and early adoption is permitted. Effective January 1, 2020, the Company early adopted this updated guidance and it did not 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, 2020
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, 2020 2019 2020 2019 Common stock options 2,415,979 2,487,135 2,262,174 2,398,467 Common stock warrants 9,092,807 9,826,743 9,451,913 10,412,385 Total 11,508,786 12,313,878 11,714,087 12,810,852

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Schedule of Short-Term Investments	The following tables summarize the Company's short-term investments (dollars in thousands): As of September 30, 2020 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 2 years or less $ 159,588 $ 576 $ — $ 160,164 Commercial paper 1 year or less 154,795 296 — 155,091 U.S. Agency bonds 2 years or less 79,120 38 (3) 79,155 U.S. Treasury bills 1 year or less 53,176 30 — 53,206 $ 446,679 $ 940 $ (3) $ 447,616 As of December 31, 2019 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 2 years or less $ 160,065 $ 233 $ (1) $ 160,297 Commercial paper 1 year or less 120,862 74 — 120,936 U.S. Agency bonds 2 years or less 50,745 41 (4) 50,782 U.S. Treasury bills 2 years or less 36,474 27 (1) 36,500 $ 368,146 $ 375 $ (6) $ 368,515

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2020
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, 2020 Total Level 1 Level 2 Level 3 Assets Cash and cash equivalents: Cash $ 18,812 $ 18,812 $ — $ — Money market funds 112,622 112,622 — — Total cash and cash equivalents 131,434 131,434 — — Short-term investments: U.S. Treasury bills 53,206 53,206 — — Corporate debt securities 160,164 — 160,164 — Commercial paper 155,091 — 155,091 — U.S. Agency bonds 79,155 — 79,155 — Total short-term investments 447,616 53,206 394,410 — Long-term investment: ORIC Pharmaceuticals 11,400 — — 11,400 Total $ 590,450 $ 184,640 $ 394,410 $ 11,400 December 31, 2019 Total Level 1 Level 2 Assets Cash and cash equivalents: Cash $ 662 $ 662 $ — Money market funds 45,873 45,873 — Total cash and cash equivalents 46,535 46,535 — Short-term investments: U.S. Treasury bills 36,500 36,500 — Corporate debt securities 160,297 — 160,297 Commercial paper 120,936 — 120,936 U.S. Agency bonds 50,782 — 50,782 Total short-term investments 368,515 36,500 332,015 Total $ 415,050 $ 83,035 $ 332,015
Schedule of Changes in Estimated Fair Value of Assets with Unobservable Inputs	The following table presents the changes in estimated fair value of the Company's asset measured using significant unobservable inputs (Level 3) (in thousands): September 30, 2020 Balance - January 1, 2020 $ — Additions 11,424 Change in fair value measurement (24) Balance - September 30, 2020 $ 11,400

Other Current Assets and Othe_2

Other Current Assets and Other Long-Term Assets (Tables)	9 Months Ended
	Sep. 30, 2020
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, 2020 2019 Prepaid expenses $ 8,892 $ 5,672 Deposits and other receivables 5,914 2,119 Interest receivable 1,535 1,566 $ 16,341 $ 9,357

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consisted of the following (in thousands): September 30, December 31, 2020 2019 Computer equipment $ 201 $ 201 Office and other equipment 329 329 Laboratory equipment 4,886 2,212 Leasehold improvements 63 63 Construction-in-progress 1,886 — Gross property and equipment 7,365 2,805 Less: Accumulated depreciation (1,464) (1,029) Property and equipment, net $ 5,901 $ 1,776

Accounts Payable, Accrued Lia_2

Accounts Payable, Accrued Liabilities and Long-Term Liabilities (Tables)	9 Months Ended
	Sep. 30, 2020
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, 2020 2019 Accounts payable $ 15,975 $ 16,367 Accrued clinical expense 35,281 21,290 Accrued development and other expense 7,414 2,510 Accrued compensation and benefits 8,000 7,915 $ 66,670 $ 48,082

License and Collaboration Agr_2

License and Collaboration Agreements (Tables)	9 Months Ended
	Sep. 30, 2020
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, 2020 (in thousands): Opening balance, January 1, 2020 $ (172) Revenue from performance obligations satisfied during reporting period 29 Closing balance, September 30, 2020 $ (143)

Warrants (Tables)

Warrants (Tables)	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Schedule of Warrants Issued and Outstanding	As of September 30, 2020, 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 4,533,224 November 20, 2017 None $ 0.001 4,137,999 June 11, 2018 None $ 0.001 421,650 9,092,873

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2020
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, 2020 2019 2020 2019 Research and development expense $ 12,556 $ 8,648 $ 35,861 $ 20,416 General and administrative expense 9,195 6,458 28,243 18,410 $ 21,751 $ 15,106 $ 64,104 $ 38,826

Description of Business - Narra

Description of Business - Narrative (Details)	9 Months Ended
	Sep. 30, 2020segment
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, 2020
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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	11,508,786	12,313,878	11,714,087	12,810,852
Common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	2,415,979	2,487,135	2,262,174	2,398,467
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	9,092,807	9,826,743	9,451,913	10,412,385

Investments - Summary (Details)

Investments - Summary (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized cost		$ 446,679	$ 368,146
Gross unrealized gains		940	375
Gross unrealized losses		(3)	(6)
Estimated fair value		$ 447,616	368,515
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Maturity	2 years	2 years
Amortized cost		$ 159,588	160,065
Gross unrealized gains		576	233
Gross unrealized losses		0	(1)
Estimated fair value		$ 160,164	160,297
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Maturity	1 year	1 year
Amortized cost		$ 154,795	120,862
Gross unrealized gains		296	74
Gross unrealized losses		0	0
Estimated fair value		$ 155,091	120,936
U.S. Agency bonds
Debt Securities, Available-for-sale [Line Items]
Maturity	2 years	2 years
Amortized cost		$ 79,120	50,745
Gross unrealized gains		38	41
Gross unrealized losses		(3)	(4)
Estimated fair value		$ 79,155	50,782
U.S. Treasury bills
Debt Securities, Available-for-sale [Line Items]
Maturity	2 years	1 year
Amortized cost		$ 53,176	36,474
Gross unrealized gains		30	27
Gross unrealized losses		0	(1)
Estimated fair value		$ 53,206	$ 36,500

Investments - Narrative (Detail

Investments - Narrative (Details)	Sep. 30, 2020USD ($)shares
Schedule of Investments [Line Items]
Allowance for credit losses on available-for-sale investments | $	$ 0
ORIC
Schedule of Investments [Line Items]
Stock held in investment (shares) | shares	588,235

Fair Value Measurements - Summa

Fair Value Measurements - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	$ 131,434	$ 46,535
Investments	447,616	368,515
Total	590,450	415,050
U.S. Treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	53,206	36,500
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	160,164	160,297
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	155,091	120,936
U.S. Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	79,155	50,782
Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	11,400
Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	18,812	662
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	112,622	45,873
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	131,434	46,535
Investments	53,206	36,500
Total	184,640	83,035
Level 1 | U.S. Treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	53,206	36,500
Level 1 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 1 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 1 | U.S. Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 1 | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0
Level 1 | Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	18,812	662
Level 1 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	112,622	45,873
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Investments	394,410	332,015
Total	394,410	332,015
Level 2 | U.S. Treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 2 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	160,164	160,297
Level 2 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	155,091	120,936
Level 2 | U.S. Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	79,155	50,782
Level 2 | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0
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
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0
Investments	0
Total	11,400
Level 3 | U.S. Treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0
Level 3 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0
Level 3 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0
Level 3 | U.S. Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0
Level 3 | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	11,400
Level 3 | Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0
Level 3 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	$ 0

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details)	Sep. 30, 2020
Volatility
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Measurement input of investment	0.88
Expected Term
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Measurement input of investment	1.3
Discount for Lack of Marketability
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Measurement input of investment	0.225

Fair Value Measurements - Chang

Fair Value Measurements - Changes in Estimated Fair Value of Assets with Unobservable Inputs (Details) - Level 3 $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 0
Additions	11,424
Change in fair value measurement	(24)
Balance at end of period	$ 11,400

Other Current Assets and Othe_3

Other Current Assets and Other Long-Term Assets - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 8,892	$ 5,672
Deposits and other receivables	5,914	2,119
Interest receivable	1,535	1,566
Other current assets	$ 16,341	$ 9,357

Other Current Assets and Othe_4

Other Current Assets and Other Long-Term Assets - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deposits paid for research and development	$ 6	$ 5.1
Long-term operating right-of-use asset	0.6	0.6
Security deposit for lease	$ 0.6	$ 0.3

Property and Equipment, Net - S

Property and Equipment, Net - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Gross property and equipment	$ 7,365	$ 2,805
Less: Accumulated depreciation	(1,464)	(1,029)
Property and equipment, net	5,901	1,776
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	329
Laboratory equipment
Property, Plant and Equipment [Line Items]
Gross property and equipment	4,886	2,212
Leasehold improvements
Property, Plant and Equipment [Line Items]
Gross property and equipment	63	63
Construction-in-progress
Property, Plant and Equipment [Line Items]
Gross property and equipment	$ 1,886	$ 0

Property and Equipment, Net - N

Property and Equipment, Net - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Property, Plant and Equipment [Abstract]
Depreciation	$ 200	$ 435	$ 156

Accounts Payable, Accrued Lia_3

Accounts Payable, Accrued Liabilities and Long-Term Liabilities - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accounts payable	$ 15,975	$ 16,367
Accrued clinical expense	35,281	21,290
Accrued development and other expense	7,414	2,510
Accrued compensation and benefits	8,000	7,915
Total accounts payable and accrued liabilities	$ 66,670	$ 48,082

Accounts Payable, Accrued Lia_4

Accounts Payable, Accrued Liabilities and Long-Term Liabilities - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Long-term liabilities	$ 1,541	$ 999

License and Collaboration Agr_3

License and Collaboration Agreements - Narrative (Details) - USD ($)	Aug. 03, 2020	Jan. 07, 2018	Oct. 31, 2014	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Expenses related to collaboration agreement				$ 79,853,000	$ 47,362,000	$ 216,644,000	$ 119,925,000
BeiGene Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Up-front fee received		$ 10,000,000
Revenue from performance obligation expected to be earned		$ 123,000,000
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						29,000
BeiGene Agreement | Licenses of Intellectual Property
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation earned				0	0	0	0	$ 9,500,000
BeiGene Agreement | Manufacturing Supply Services
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation earned							2,600,000	$ 500,000
Payments received in advance				0	(1,000,000)	(300,000)	(2,800,000)
Revenue from performance obligations satisfied during reporting period							200,000
BeiGene Agreement | 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
BeiGene Agreement | Royalties
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue				0	0	0	0
Pfizer Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Termination of contract, period after first commercial sale of product			10 years
Period required for notice of termination of contract			60 days
Expenses related to collaboration agreement				$ 300,000	$ 1,500,000	4,800,000	5,500,000
Pfizer Agreement | Milestone Payments
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Expenses related to collaboration agreement							1,000,000
Pfizer Agreement | Research and Development Services
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Expenses related to collaboration agreement						$ 1,500,000	$ 4,500,000
ORIC Pharmaceuticals Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Stock received as part of stock issuance and license agreements (shares)	588,235
License agreement, period of transfer restrictions	18 months
License agreement, period of agreement after first commercial sale	10 years
ORIC Pharmaceuticals Agreement | Level 3
Research and Development Arrangement, Contract to Perform for Others [Line Items]
License agreement, transaction price	$ 11,400,000

License and Collaboration Agr_4

License and Collaboration Agreements - Activity in Contract Liabilities (Details) - BeiGene Agreement $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Movement in Deferred Revenue [Roll Forward]
Opening balance at beginning of period	$ (172)
Revenue from performance obligations satisfied during reporting period	29
Closing balance at end of period	$ (143)

Warrants - Summary (Details)

Warrants - Summary (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Class of Warrant or Right [Line Items]
Number of warrants outstanding (shares)	9,092,873		9,092,873
Warrants exercised via cashless exercises (shares)	0	725,008	600,006	2,125,033
Common stock issued from exercise of warrants (shares)		725,000	600,000	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)	4,533,224		4,533,224
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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Right-of-use asset	$ 600,000		$ 600,000		$ 600,000
Current Headquarters
Lessee, Lease, Description [Line Items]
Minimum monthly rental expense			$ 4,000
Discount rate (as a percent)	12.00%		12.00%
Operating lease cost	$ 100,000	$ 100,000	$ 200,000	$ 300,000
Remaining lease term	1 year		1 year
Right-of-use asset	$ 600,000		$ 600,000
Operating lease liability	600,000		600,000
Remaining lease payments for remainder of fiscal year	100,000		100,000
Remaining lease payments for next year	100,000		100,000
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			$ 600,000
Annual rent increase (as a percent)	3.00%		3.00%
Lease term	12 years		12 years

Shareholders' Equity - Narrativ

Shareholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended		9 Months Ended
	Jan. 31, 2020	Jun. 30, 2019	Jan. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jul. 02, 2020	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Common stock, par value (USD per share)				$ 0.001		$ 0.001		$ 0.001	$ 0.001
Aggregate offering price								$ 200,000
Stock issued in transaction (shares)	3,538,462	2,415,000	1,854,838
Sale price of common stock (USD per share)	$ 97.50		$ 62		$ 97		$ 97
Proceeds from sale of stock	$ 324,000	$ 219,900	$ 107,900
Stock issued pursuant to stock option exercises (shares)				272,158	91,257	1,092,468	424,144
Proceeds from stock options exercised				$ 12,400	$ 1,100	$ 36,300	$ 5,400
Proceeds from disgorgement of shareholders' short-swing profits			$ 1,100			$ 41	$ 1,050

Shareholders' Equity - Summary

Shareholders' Equity - Summary (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	$ 21,751	$ 15,106	$ 64,104	$ 38,826
Research and development expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	12,556	8,648	35,861	20,416
General and administrative expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	$ 9,195	$ 6,458	$ 28,243	$ 18,410

Subsequent Event - Narrative (D

Subsequent Event - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Oct. 31, 2020	Jan. 31, 2020	Jun. 30, 2019	Jan. 31, 2019	Sep. 30, 2019
Subsequent Event [Line Items]
Stock issued in transaction (shares)		3,538,462	2,415,000	1,854,838
Sale price of common stock (USD per share)		$ 97.50		$ 62	$ 97
Proceeds from sale of stock		$ 324	$ 219.9	$ 107.9
Subsequent Event | Common Stock
Subsequent Event [Line Items]
Stock issued in transaction (shares)	4,585,706
Sale price of common stock (USD per share)	$ 202
Proceeds from sale of stock	$ 879.7

Uncategorized Items - mrtx-2020

Label	Element	Value
Restricted Cash	us-gaap_RestrictedCash	$ 620,000
Restricted Cash	us-gaap_RestrictedCash	320,000
Pfizer Discovery and Collaboration Agreement [Member] | Sales Milestone Payments [Member]
Research and Development Arrangement, Discovery and Collaboration Agreement, Compensation Expected to be Paid	mrtx_ResearchandDevelopmentArrangementDiscoveryandCollaborationAgreementCompensationExpectedtobePaid	337,000,000
Pfizer Discovery and Collaboration Agreement [Member] | Milestone Payments - Initiation of First Phase 2 Trial for MRTX849 [Member]
Research and Development Expense	us-gaap_ResearchAndDevelopmentExpense	3,000,000
Pfizer Discovery and Collaboration Agreement [Member] | Milestone Payments - Initiation of First Regulatory Toxicology Study for MRTX1133 [Member]
Research and Development Expense	us-gaap_ResearchAndDevelopmentExpense	300,000
Pfizer Discovery and Collaboration Agreement [Member] | Development Milestone Payments [Member]
Research and Development Arrangement, Discovery and Collaboration Agreement, Compensation Expected to be Paid	mrtx_ResearchandDevelopmentArrangementDiscoveryandCollaborationAgreementCompensationExpectedtobePaid	9,300,000
Research and Development Arrangement, Discovery and Collaboration Agreement, Milestone Payments Paid	mrtx_ResearchandDevelopmentArrangementDiscoveryandCollaborationAgreementMilestonePaymentsPaid	$ 4,500,000