Jointly owned facilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Jointly owned electricity generation plant \| Big Stone Station
Jointly Owned Utility Plant Interests [Line Items]
Proportionate ownership share	22.70%
Utility plant in service	$ 157,699	$ 157,259
Construction work in progress	231	571
Less accumulated depreciation	48,590	47,293
Utility plant in services net	$ 109,340	110,537
Jointly owned electricity generation plant \| Coyote Station
Jointly Owned Utility Plant Interests [Line Items]
Proportionate ownership share	25.00%
Utility plant in service	$ 158,274	157,764
Construction work in progress	1,807	784
Less accumulated depreciation	111,203	109,202
Utility plant in services net	$ 48,878	49,346
Jointly owned electricity generation plant \| Wygen III
Jointly Owned Utility Plant Interests [Line Items]
Proportionate ownership share	25.00%
Utility plant in service	$ 66,238	66,357
Construction work in progress	273	108
Less accumulated depreciation	12,477	11,383
Utility plant in services net	$ 54,034	55,082
Jointly Owned Electricity Transmission and Distribution System \| BSSE
Jointly Owned Utility Plant Interests [Line Items]
Proportionate ownership share	50.00%
Utility plant in service	$ 107,260	107,424
Construction work in progress	0	0
Less accumulated depreciation	6,182	4,506
Utility plant in services net	$ 101,078	$ 102,918

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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 360
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.C)
-URI https://asc.fasb.org/extlink&oid=122136288&loc=d3e659983-123033

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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 total period end amount of plant in service and construction in progress net of accumulated depreciation for the utility's share of jointly owned electricity generation plant.

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- Definition

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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