Income Taxes - Deferred Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred Tax Liabilities, Gross
Deferred Tax Liabilities, Property, Plant and Equipment	$ 1,892,674	$ 1,923,933
Deferred Tax Liabilities, Other	202,783	175,333
Deferred Tax Liabilities, Gross, Total	2,095,457	2,099,266
Deferred Tax Assets, Gross
Deferred Tax Assets, Operating Loss Carryforwards	(254,007)	(261,260)
Deferred Tax Assets, Net Regulatory Liability for Income Taxes	(865,976)	(953,274)
Deferred Tax Assets, Tax Credit Carryforwards, Production	0	(35,995)
Deferred Tax Assets, Other	(62,990)	(38,008)
Deferred Tax Assets, Gross	(1,182,973)	(1,288,537)
Deferred Tax Liabilities, Net, Total	912,484	810,729
Subsidiaries [Member]
Deferred Tax Liabilities, Gross
Deferred Tax Liabilities, Property, Plant and Equipment	1,892,674	1,923,933
Deferred Tax Liabilities, Other	121,060	91,438
Deferred Tax Liabilities, Gross, Total	2,013,734	2,015,371
Deferred Tax Assets, Gross
Deferred Tax Assets, Net Regulatory Liability for Income Taxes	(866,541)	(953,987)
Deferred Tax Assets, Tax Credit Carryforwards, Production	0	(35,995)
Deferred Tax Assets, Other	(62,990)	(38,007)
Deferred Tax Assets, Gross	(929,531)	(1,027,989)
Deferred Tax Liabilities, Net, Total	$ 1,084,203	$ 987,382