PROPERTY, PLANT AND EQUIPMENT - Jointly Owned Facilities (Details) $ in Thousands |
Mar. 31, 2026
USD ($)
|
|---|---|
| Jointly Owned Utility Plant Interests [Line Items] | |
| Electric Plant in Service | $ 936,120 |
| Accumulated Depreciation | 744,281 |
| Construction Work In Progress | $ 4,588 |
| Yampa Project - Craig Generating Station Units 1 and 2 | |
| Jointly Owned Utility Plant Interests [Line Items] | |
| Tri-State Share (as a percent) | 24.00% |
| Electric Plant in Service | $ 392,520 |
| Accumulated Depreciation | 380,700 |
| Construction Work In Progress | $ 0 |
| MBPP - Laramie River Station | |
| Jointly Owned Utility Plant Interests [Line Items] | |
| Tri-State Share (as a percent) | 28.50% |
| Electric Plant in Service | $ 543,600 |
| Accumulated Depreciation | 363,581 |
| Construction Work In Progress | $ 4,588 |