| Cover | Dec. 20, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Dec. 20, 2021 |
| Entity Registrant Name | TRI-STATE GENERATION AND TRANSMISSION ASSOCIATION, INC. |
| Entity Incorporation, State or Country Code | CO |
| Entity File Number | 333-212006 |
| Entity Tax Identification Number | 84-0464189 |
| Entity Address, Address Line One | 1100 W. 116th Avenue |
| Entity Address, City or Town | Westminster, |
| Entity Address, State or Province | CO |
| Entity Address, Postal Zip Code | 80234 |
| City Area Code | 303 |
| Local Phone Number | 452-6111 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001637880 |
