Label	Element	Value
Restricted Cash	us-gaap_RestrictedCash	$ 0
Restricted Cash	us-gaap_RestrictedCash	620,000
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	4,300,000
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	$ 337,000,000.0