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Select Balance Sheet Information - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands | Mar. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Property, Plant and Equipment [Line Items] |  |
Property, Plant and Equipment, net of accumulated depreciation | $ 2,128,344 | $ 2,124,605
Electric Plant |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 2,849,125 | 2,833,371
Less Accumulated Depreciation and Amortization | 829,499 | 817,302
Property, Plant and Equipment, net of accumulated depreciation | 2,019,626 | 2,016,069
Nonelectric Property, Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 293,094 | 290,561
Less Accumulated Depreciation and Amortization | 184,376 | 182,025
Property, Plant and Equipment, net of accumulated depreciation | 108,718 | 108,536
Electric Plant in Service | Electric Plant |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 2,776,778 | 2,758,445
Construction Work in Progress | Electric Plant |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 72,347 | 74,926
Construction Work in Progress | Nonelectric Property, Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 14,365 | 16,611
Nonelectric Property, Plant and Equipment in Service | Nonelectric Property, Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | $ 278,729 | $ 273,950

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