INVESTMENT TAX CREDITS (Details) (USD $)	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
INVESTMENT TAX CREDITS
Refundable investment tax credits recorded as a reduction of research and development expenses	$ 253,000	$ 91,000	$ 482,000	$ 1,400,000

The amount of tax credit payment received from a taxing authority based on eligible research and development expenditures.

No definition available.

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