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Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
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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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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