EMPLOYEE BENEFIT PLANS - Postretirement Benefits Other than Pensions - Obligations (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2025 USD ($) plan
Medical Benefit Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Total postretirement and postemployment medical obligations at end of period	$ 542
Postretirement Medical Benefit Plans
Defined Contribution Plan Disclosure [Line Items]
Threshold of unrecognized amount of actuarial gains and losses as a proportion of projected benefit obligation (as a percent)	10.00%
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Postretirement medical benefit obligation at beginning of period	$ 509
Interest cost	16
Benefit payments (net of contributions by participants)	(158)
Total postretirement and postemployment medical obligations at end of period	367
Postemployment Medical Benefit Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Total postretirement and postemployment medical obligations at end of period	$ 175
Executive Benefit Restoration Plan
Defined Contribution Plan Disclosure [Line Items]
Threshold of unrecognized amount of actuarial gains and losses as a proportion of projected benefit obligation (as a percent)	10.00%
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Postretirement medical benefit obligation at beginning of period	$ 7,918
Interest cost	260
Total postretirement and postemployment medical obligations at end of period	$ 8,400
Non-bargaining unit employees \| Medical Benefit Plans
Defined Contribution Plan Disclosure [Line Items]
Number of plans \| plan	3
Non-bargaining unit employees \| Medical Benefit Plans \| Maximum
Defined Contribution Plan Disclosure [Line Items]
Qualifying age	65 years
Non-bargaining unit employees \| Postretirement Medical Benefit Plans
Defined Contribution Plan Disclosure [Line Items]
Number of plans \| plan	2
Non-bargaining unit employees \| Postretirement Medical Benefit Plans \| Minimum
Defined Contribution Plan Disclosure [Line Items]
Qualifying age	55 years
Non-bargaining unit employees \| Postemployment Medical Benefit Plans
Defined Contribution Plan Disclosure [Line Items]
Number of plans \| plan	3

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