Select Balance Sheet Information - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, net of accumulated depreciation	$ 2,604,869	$ 2,418,375
Electric Plant
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,318,715	3,127,093
Less Accumulated Depreciation and Amortization	885,075	851,148
Property, Plant and Equipment, net of accumulated depreciation	2,433,640	2,275,945
Nonelectric Property, Plant and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	391,707	349,986
Less Accumulated Depreciation and Amortization	220,478	207,556
Property, Plant and Equipment, net of accumulated depreciation	171,229	142,430
Electric Plant in Service | Electric Plant
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,087,286	2,989,881
Construction Work in Progress | Electric Plant
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	231,429	137,212
Construction Work in Progress | Nonelectric Property, Plant and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	62,581	38,062
Nonelectric Property, Plant and Equipment in Service | Nonelectric Property, Plant and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 329,126	$ 311,924