Class of Warrant or Right, Number of Warrants Exercised, Noncash

No definition available.

Name:	mrtx_ClassofWarrantorRightNumberofWarrantsExercisedNoncash
Namespace Prefix:	mrtx_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of stock issued on warrant exercises during the period.

+ References

No definition available.

+ Details

Name:	mrtx_StockIssuedDuringPeriodSharesWarrantsExercisedNoncash
Namespace Prefix:	mrtx_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=123467817&loc=d3e21475-112644

+ Details

Name:	us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Number of warrants or rights outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_ClassOfWarrantOrRightOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_ClassOfWarrantOrRightAxis=mrtx_ClassofWarrantsIssuedJanuary112017Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ClassOfWarrantOrRightAxis=mrtx_ClassofWarrantsIssuedNovember202017Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ClassOfWarrantOrRightAxis=mrtx_ClassofWarrantsIssuedJune112018Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Warrants - Summary (Details) - $ / shares	3 Months Ended		9 Months Ended
Warrants - Summary (Details) - $ / shares	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Class of Warrant or Right [Line Items]
Number of warrants outstanding (shares)	7,605,811		7,605,811
Warrants exercised via cashless exercises (shares)	0	0	623,821	600,006
Common stock issued from exercise of warrants (shares)			623,814	600,000
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)	3,578,036		3,578,036
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)	3,669,360		3,669,360
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)	358,415		358,415