| Document and Entity Information | Oct. 27, 2020 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001576263 |
| Document Type | 8-K |
| Document Period End Date | Oct. 27, 2020 |
| Entity Registrant Name | MIRATI THERAPEUTICS, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-35921 |
| Entity Tax Identification Number | 46-2693615 |
| Entity Address, Address Line One | 9393 Towne Centre Drive |
| Entity Address, Address Line Two | Suite 200 |
| Entity Address, City or Town | San Diego |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 92121 |
| City Area Code | (858) |
| Local Phone Number | 332-3410 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock |
| Trading Symbol | MRTX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
