Accounting For Income Taxes - Schedule of Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred income tax assets:
Regulatory liabilities	$ 192,099	$ 197,998
Tax credits and net operating loss carryforwards	76,969	74,782
Provisions for pensions	19,100	20,132
Other	47,839	54,903
Total gross deferred income tax assets	336,007	347,815
Valuation allowances for deferred tax assets	(10,461)	(3,874)
Total deferred income tax assets after valuation allowances	325,546	343,941
Deferred income tax liabilities:
Utility property, plant, and equipment	746,876	712,470
Regulatory assets	268,833	281,483
Other	28,155	24,983
Total deferred income tax liabilities	1,043,864	1,018,936
Net long-term deferred income tax liability	$ 718,318	$ 674,995