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Property, Plant and Equipment - Schedule of Jointly Owned Utility Plants (Details) - USD ($) $ in Thousands | Dec. 31, 2024 | Dec. 31, 2023
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Big Stone Plant |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Electric Plant in Service | $ 345,990 | $ 341,683
Construction Work in Progress | 459 | 820
Accumulated Depreciation | (135,065) | (126,904)
Net Plant | $ 211,384 | $ 215,599
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 | $ 188,066 | $ 188,656
Construction Work in Progress | 813 | 104
Accumulated Depreciation | (118,268) | (115,306)
Net Plant | $ 70,611 | $ 73,454
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 | $ 106,185 | $ 106,185
Construction Work in Progress | 0 | 0
Accumulated Depreciation | (8,445) | (7,181)
Net Plant | $ 97,740 | $ 99,004
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 | (12,247) | (11,238)
Net Plant | $ 65,937 | $ 66,946
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 | $ 53,167 | $ 53,170
Construction Work in Progress | 0 | 0
Accumulated Depreciation | (5,822) | (5,207)
Net Plant | $ 47,345 | $ 47,963
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 | $ 28,013 | $ 26,409
Construction Work in Progress | 1,131 | 83
Accumulated Depreciation | (3,941) | (3,617)
Net Plant | $ 25,203 | $ 22,875
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 | (3,693) | (3,568)
Net Plant | $ 12,638 | $ 12,763
Bemidji–Grand Rapids 230 kV line | OTP |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Ownership Percentage | 14.80% | 14.80%
Jamestown– Ellendale 345 kV line |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Electric Plant in Service | $ 0 | $ 0
Construction Work in Progress | 5,509 | 1,121
Accumulated Depreciation | 0 | 0
Net Plant | $ 5,509 | $ 1,121
Jamestown– Ellendale 345 kV line | OTP |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Ownership Percentage | 50.00% | 50.00%
Big Stone South–Alexandria 345 kV line |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Electric Plant in Service | $ 0 | $ 0
Construction Work in Progress | 2,418 | 555
Accumulated Depreciation | 0 | 0
Net Plant | $ 2,418 | $ 555
Big Stone South–Alexandria 345 kV line | OTP |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Ownership Percentage | 40.00% | 40.00%
Alexandria–Big Oaks 345 kV line |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Electric Plant in Service | $ 0 | $ 0
Construction Work in Progress | 417 | 343
Accumulated Depreciation | 0 | 0
Net Plant | $ 417 | $ 343
Alexandria–Big Oaks 345 kV line | OTP |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Ownership Percentage | 14.20% | 14.20%
Oslo - Lake Ardoch 115 kV line |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Electric Plant in Service | $ 0 |
Construction Work in Progress | 2,646 |
Accumulated Depreciation | 0 |
Net Plant | $ 2,646 |
Oslo - Lake Ardoch 115 kV line | OTP |  |
Jointly Owned Utility Plant Interests [Line Items] |  |
Ownership Percentage | 72.00% |

X
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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 -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 + 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 -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 + Details
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