| Cover | Aug. 20, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Aug. 20, 2020 |
| Entity Registrant Name | MIRAGEN THERAPEUTICS, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-36483 |
| Entity Tax Identification Number | 47-1187261 |
| Entity Address, Address Line One | 6200 Lookout Rd. |
| Entity Address, City or Town | Boulder |
| Entity Address, State or Province | CO |
| Entity Address, Postal Zip Code | 80301 |
| City Area Code | 720 |
| Local Phone Number | 643-5200 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.01 par value |
| Trading Symbol | MGEN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001590750 |
