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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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Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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