PROPERTY, PLANT AND EQUIPMENT - Electric Plant (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Electric Plant
Accumulated Depreciation	$ (2,931,693)	$ (2,838,877)
Construction work in progress	511,309	368,473
Net electric plant	3,398,202	3,230,778
Electric Plant
Electric Plant
Plant In Service	5,818,586	5,701,182
Accumulated Depreciation	(2,931,693)	(2,838,877)
Net Book Value	2,886,893	2,862,305
Construction work in progress	511,309	368,473
Net electric plant	3,398,202	3,230,778
Generation plant
Electric Plant
Plant In Service	3,096,017	3,100,656
Accumulated Depreciation	(1,803,679)	(1,744,837)
Net Book Value	$ 1,292,338	$ 1,355,819
Generation plant \| Minimum
Electric Plant
Annual Depreciation Rate (as a percent)	1.14%	1.14%
Generation plant \| Maximum
Electric Plant
Annual Depreciation Rate (as a percent)	4.14%	4.14%
Transmission plant
Electric Plant
Plant In Service	$ 2,042,453	$ 1,933,206
Accumulated Depreciation	(734,446)	(715,505)
Net Book Value	$ 1,308,007	$ 1,217,701
Transmission plant \| Minimum
Electric Plant
Annual Depreciation Rate (as a percent)	1.17%	1.17%
Transmission plant \| Maximum
Electric Plant
Annual Depreciation Rate (as a percent)	1.84%	1.84%
General plant
Electric Plant
Plant In Service	$ 437,720	$ 426,615
Accumulated Depreciation	(292,185)	(279,678)
Net Book Value	$ 145,535	$ 146,937
General plant \| Minimum
Electric Plant
Annual Depreciation Rate (as a percent)	1.20%	1.20%
General plant \| Maximum
Electric Plant
Annual Depreciation Rate (as a percent)	11.60%	11.60%
Other
Electric Plant
Plant In Service	$ 242,396	$ 240,705
Accumulated Depreciation	(101,383)	(98,857)
Net Book Value	$ 141,013	$ 141,848
Other \| Minimum
Electric Plant
Annual Depreciation Rate (as a percent)	2.75%	2.75%
Other \| Maximum
Electric Plant
Annual Depreciation Rate (as a percent)	10.00%	10.00%

Tri-State Generation & Transmission Association, Inc. 10-Q