| Document and Entity Information | Feb. 10, 2021 |
| Cover [Abstract] | |
| Security Exchange Name | NASDAQ |
| Amendment Flag | false |
| Entity Central Index Key | 0001183765 |
| Document Type | 8-K |
| Document Period End Date | Feb. 10, 2021 |
| Entity Registrant Name | Molecular Templates, Inc. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-32979 |
| Entity Tax Identification Number | 94-3409596 |
| Entity Address, Address Line One | 9301 Amberglen Blvd |
| Entity Address, Address Line Two | Suite 100 |
| Entity Address, City or Town | Austin |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 78729 |
| City Area Code | (512) |
| Local Phone Number | 869-1555 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $0.001 Par Value Per Share |
| Trading Symbol | MTEM |
| Entity Emerging Growth Company | false |
