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Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands | Dec. 31, 2021 | Dec. 31, 2020
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Property, Plant and Equipment [Line Items] |  |
Property, Plant and Equipment, net of accumulated depreciation | $ 2,124,605 | $ 2,049,273
Electric Plant in Service |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 2,833,371 | 2,734,430
Less Accumulated Depreciation and Amortization | 817,302 | 778,988
Property, Plant and Equipment, net of accumulated depreciation | 2,016,069 | 1,955,442
Nonelectric Property, Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 290,561 | 268,020
Less Accumulated Depreciation and Amortization | 182,025 | 174,189
Property, Plant and Equipment, net of accumulated depreciation | 108,536 | 93,831
Production | Electric Plant in Service |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 1,332,067 | 1,172,362
Transmission | Electric Plant in Service |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 722,739 | 690,647
Distribution | Electric Plant in Service |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 574,488 | 545,221
General | Electric Plant in Service |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 129,151 | 123,122
Electric Plant in Service | Electric Plant in Service |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 2,758,445 | 2,531,352
Construction Work in Progress | Electric Plant in Service |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 74,926 | 203,078
Construction Work in Progress | Nonelectric Property, Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 16,611 | 9,290
Equipment | Nonelectric Property, Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 203,390 | 197,389
Buildings and Leasehold Improvements | Nonelectric Property, Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 56,908 | 55,441
Land | Nonelectric Property, Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 13,652 | 5,900
Nonelectric Property, Plant and Equipment | Nonelectric Property, Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | $ 273,950 | $ 258,730

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