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License Agreement, One-Time Non-Cash Payment, Number of Shares Received

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License Agreement, Period of Agreement after First Commercial Sale

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License Agreement, Period of Transfer Restrictions

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Research and Development Arrangement, Contract to Perform for Others, Compensation Expected to be Earned

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Research and Development Arrangement, Contract to Perform for Others, Period Required for Notice of Termination of Contract

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Research and Development Arrangement, Contract to Perform for Others, Termination of Contract, Period after First Commercial Sale of Product

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Research and Development Arrangement, Discovery and Collaboration Agreement, Period Required for Notice of Termination of Contract

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Research and Development Arrangement, Discovery and Collaboration Agreement, Termination of Contract, Period after First Commercial Sale of Product

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Research and Development Arrangement, Up-Front Fee Received

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Amount, before allowance for credit loss, of right to consideration in exchange for good or service transferred to customer, when right is conditioned on something other than passage of time.

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Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

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Amount of increase (decrease) in obligation to transfer good or service to customer for which consideration has been received or is receivable.

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The amount of compensation earned (contract income) under a research and development arrangement accounted for as a contract to perform research and development for others.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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Ancillary revenue earned during the period from the consideration paid to the entity for the use of its rights and property by another party. Examples include licensing the use of copyrighted materials and leasing the extraction of natural resources.

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License and Collaboration Agreements - Narrative (Details) - USD ($)			1 Months Ended	12 Months Ended
	Aug. 03, 2020	Jan. 07, 2018	Oct. 31, 2014	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Expenses related to collaboration agreement				$ 299,349,000	$ 182,866,000	$ 93,872,000
BeiGene Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Up-front fee received		$ 10,000,000.0
Revenue from performance obligation expected to be earned		$ 123,000,000.0
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 obligation earned						500,000
Revenue from performance obligations satisfied during reporting period				172,000
BeiGene Agreement \| Licenses of Intellectual Property
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation earned				0	0	9,500,000
BeiGene Agreement \| Manufacturing Supply Services
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation earned				1,800,000	3,000,000.0	400,000
Revenue recognized				(2,000,000.0)	(3,300,000)	(500,000)
Revenue from performance obligations satisfied during reporting period				200,000	300,000	100,000
Cost sharing receivable				1,300,000	400,000
BeiGene Agreement \| Milestone Payments
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation expected to be earned				5,000,000.0
Revenue recognized				0	0	3,000,000.0
BeiGene Agreement \| Royalties
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue				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				4,800,000	7,000,000.0	6,400,000
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	$ 6,000,000.0	4,100,000
Pfizer Agreement \| Option Fee - Exclusive License to Develop and Commercialize MRTX1133
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Expenses related to collaboration agreement						$ 2,000,000.0
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