PROPERTY, PLANT AND EQUIPMENT - Jointly Owned Facilities (Details) $ in Thousands	Sep. 30, 2024 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Electric Plant in Service	$ 937,966
Accumulated Depreciation	717,265
Construction Work In Progress	$ 8,928
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	$ 392,510
Accumulated Depreciation	365,379
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	$ 545,456
Accumulated Depreciation	351,886
Construction Work In Progress	$ 8,928

The period end amount owned by the reporting utility of a jointly owned utility plant in service.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 360
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.C)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479070/980-360-S99-1

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The period end amount of construction work in progress at a jointly owned electricity generation plant.

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- Definition

The period end amount of accumulated depreciation in a jointly owned electricity generation plant.

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- Definition

The proportionate share of interest (percent) in a jointly owned utility plant.

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