Name:	mrtx_CollaborationArrangementResearchAndDevelopmentArrangementContractToPerformForOthersCompensationExpectedToBeEarned
Namespace Prefix:	mrtx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

No definition available.

Name:	mrtx_CollaborationArrangementResearchAndDevelopmentArrangementContractToPerformForOthersPeriodRequiredForNoticeOfTerminationOfContract
Namespace Prefix:	mrtx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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

No definition available.

Name:	mrtx_CollaborationArrangementResearchAndDevelopmentArrangementContractToPerformForOthersTerminationOfContractPeriodAfterFirstCommercialSaleOfProduct
Namespace Prefix:	mrtx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Collaboration Arrangement, Research and Development Arrangement, Transaction Price

No definition available.

Name:	mrtx_CollaborationArrangementResearchAndDevelopmentArrangementTransactionPrice
Namespace Prefix:	mrtx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Collaboration Arrangement, Research and Development Arrangement, Up-Front Fee Received

No definition available.

Name:	mrtx_CollaborationArrangementResearchAndDevelopmentArrangementUpFrontFeeReceived
Namespace Prefix:	mrtx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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

No definition available.

Name:	mrtx_CollaborativeArrangementResearchAndDevelopmentArrangementDiscoveryAndCollaborationAgreementPeriodRequiredForNoticeOfTerminationOfContract
Namespace Prefix:	mrtx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Collaborative Arrangement, Research and Development Arrangement, Discovery and Collaboration Agreement, Royalty Percentage

No definition available.

Name:	mrtx_CollaborativeArrangementResearchAndDevelopmentArrangementDiscoveryAndCollaborationAgreementRoyaltyPercentage
Namespace Prefix:	mrtx_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

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

No definition available.

Name:	mrtx_CollaborativeArrangementResearchAndDevelopmentArrangementDiscoveryAndCollaborationAgreementTerminationOfContractPeriodAfterFirstCommercialSaleOfProduct
Namespace Prefix:	mrtx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Contract with Customer, Milestone Payments Receivable

No definition available.

Name:	mrtx_ContractwithCustomerMilestonePaymentsReceivable
Namespace Prefix:	mrtx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

License Agreement, One-Time Non-Cash Payment

No definition available.

Name:	mrtx_LicenseAgreementOneTimeNonCashPayment
Namespace Prefix:	mrtx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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

No definition available.

Name:	mrtx_LicenseAgreementOneTimeNonCashPaymentNumberOfSharesReceived
Namespace Prefix:	mrtx_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

License Agreement, Period of Agreement after First Commercial Sale

No definition available.

Name:	mrtx_LicenseAgreementPeriodOfAgreementAfterFirstCommercialSale
Namespace Prefix:	mrtx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

License Agreement, Period of Transfer Restrictions

No definition available.

Name:	mrtx_LicenseAgreementPeriodOfTransferRestrictions
Namespace Prefix:	mrtx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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

No definition available.

Name:	mrtx_ResearchandDevelopmentArrangementContracttoPerformforOthersCompensationExpectedtobeEarned
Namespace Prefix:	mrtx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Research and Development Arrangement, Discovery and Collaboration Agreement, Compensation Expected to be Paid

No definition available.

Name:	mrtx_ResearchandDevelopmentArrangementDiscoveryandCollaborationAgreementCompensationExpectedtobePaid
Namespace Prefix:	mrtx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Research and Development Arrangement, Discovery and Collaboration Agreement, Milestone Payments Paid

No definition available.

Name:	mrtx_ResearchandDevelopmentArrangementDiscoveryandCollaborationAgreementMilestonePaymentsPaid
Namespace Prefix:	mrtx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Research and Development Arrangement, Up-Front Fee Received

No definition available.

Name:	mrtx_ResearchandDevelopmentArrangementUpFrontFeeReceived
Namespace Prefix:	mrtx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.7)
-URI https://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 10
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32672-109319

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (h)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8736-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI https://asc.fasb.org/extlink&oid=124431687&loc=d3e22663-107794

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 20
-Section 45
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=123586238&loc=d3e38679-109324

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(9))
-URI https://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 8
-URI https://asc.fasb.org/extlink&oid=124431687&loc=d3e22658-107794

Name:	us-gaap_IncomeTaxExpenseBenefit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 730
-SubTopic 20
-Section 50
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=6420387&loc=d3e23221-108380

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 730
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=6420387&loc=d3e23199-108380

Name:	us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersCompensationEarned
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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.

No definition available.

Name:	us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 912
-SubTopic 730
-Section 25
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6472174&loc=d3e58812-109433

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 730
-SubTopic 10
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6420194&loc=d3e21568-108373

Name:	us-gaap_ResearchAndDevelopmentExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9038-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130545-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8906-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8736-108599

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8736-108599

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130543-203045

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9054-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9031-108599

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 924
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-URI https://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

Name:	us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7)
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

Name:	us-gaap_RoyaltyIncomeNonoperating
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Name:	us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis=mrtx_BeiGeneCollaborationandLicenseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis=us-gaap_LicenseAgreementTermsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis=mrtx_ManufacturingSupplyServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis=mrtx_PfizerDiscoveryandCollaborationAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_ProductOrServiceAxis=mrtx_AdagrasibMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	mrtx_ResearchandDevelopmentArrangementDiscoveryandCollaborationAgreementTypeAxisAxis=mrtx_DevelopmentMilestonePaymentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	mrtx_ResearchandDevelopmentArrangementDiscoveryandCollaborationAgreementTypeAxisAxis=mrtx_SalesMilestonePaymentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis=mrtx_ORICPharmaceuticalsAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis=mrtx_ZaiCollaborationAndLicenseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis=mrtx_SalesMilestonePaymentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis=mrtx_DevelopmentAndRegulatoryBasedMilestonePaymentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: