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Property, Plant and Equipment - Jointly Owned Utility Plants (Details) - USD ($) $ in Thousands | Dec. 31, 2021 | Dec. 31, 2020
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Big Stone Plant |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Electric Plant in Service | $ 338,699 | $ 332,611
Construction Work in Progress | 260 | 2,552
Accumulated Depreciation | (110,604) | (103,504)
Net Plant | $ 228,355 | $ 231,659
Big Stone Plant | OTP |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Ownership Percentage | 53.90% | 53.90%
Coyote Station |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Electric Plant in Service | $ 182,610 | $ 180,991
Construction Work in Progress | 1,110 | 732
Accumulated Depreciation | (107,894) | (108,603)
Net Plant | $ 75,826 | $ 73,120
Coyote Station | OTP |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Ownership Percentage | 35.00% | 35.00%
Big Stone South–Ellendale 345 kV line |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Electric Plant in Service | $ 106,194 | $ 106,353
Construction Work in Progress | 0 | 0
Accumulated Depreciation | (4,052) | (2,433)
Net Plant | $ 102,142 | $ 103,920
Big Stone South–Ellendale 345 kV line | OTP |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Ownership Percentage | 50.00% | 50.00%
Fargo–Monticello 345 kV line |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Electric Plant in Service | $ 78,184 | $ 78,184
Construction Work in Progress | 0 | 0
Accumulated Depreciation | (9,069) | (8,029)
Net Plant | $ 69,115 | $ 70,155
Fargo–Monticello 345 kV line | OTP |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Ownership Percentage | 14.20% | 14.20%
Big Stone South–Brookings 345 kV line |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Electric Plant in Service | $ 52,975 | $ 53,036
Construction Work in Progress | 0 | 0
Accumulated Depreciation | (3,613) | (2,822)
Net Plant | $ 49,362 | $ 50,214
Big Stone South–Brookings 345 kV line | OTP |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Ownership Percentage | 50.00% | 50.00%
Brookings–Southeast Twin Cities 345 kV line |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Electric Plant in Service | $ 26,291 | $ 26,291
Construction Work in Progress | 0 | 0
Accumulated Depreciation | (2,843) | (2,468)
Net Plant | $ 23,448 | $ 23,823
Brookings–Southeast Twin Cities 345 kV line | OTP |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Ownership Percentage | 4.80% | 4.80%
Bemidji–Grand Rapids 230 kV line |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Electric Plant in Service | $ 16,331 | $ 16,331
Construction Work in Progress | 0 | 0
Accumulated Depreciation | (2,995) | (2,670)
Net Plant | $ 13,336 | $ 13,661
Bemidji–Grand Rapids 230 kV line | OTP |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Ownership Percentage | 14.80% | 14.80%

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- Definition The period end amount of construction work in progress, or the deficit in the construction work in progress, at a jointly owned electricity generation plant. + References No definition available. + Details
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- Definition The period end amount owned by the reporting utility of a jointly owned utility plant in service. + References 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 http://asc.fasb.org/extlink&oid=122136288&loc=d3e659983-123033 + Details
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- Definition 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. + References 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 http://asc.fasb.org/extlink&oid=122136288&loc=d3e659983-123033 + Details
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