| Cover Page | Feb. 25, 2021 |
| Cover [Abstract] | |
| Entity Central Index Key | 0001576263 |
| Amendment Flag | false |
| Document Type | 8-K |
| Document Period End Date | Feb. 25, 2021 |
| Entity Registrant Name | MIRATI THERAPEUTICS, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-35921 |
| Entity Tax Identification Number | 46-2693615 |
| Entity Address, Address Line One | 9393 Towne Centre Drive, 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 |
| Entity Emerging Growth Company | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | MRTX |
| Security Exchange Name | NASDAQ |
