Income Taxes - Schedule of Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Deferred tax assets:
Environmental compliance	$ 33,730	$ 28,873
Pension and postretirement	25,508	27,584
Compensation-related	15,651	17,106
Customer advances	9,719	8,312
Cost recovery mechanisms	7,402	5,314
Legal and environmental contingencies	5,317	4,881
Other	20,386	13,045
Total deferred tax assets	117,713	105,115
Deferred tax liabilities:
Basis differences on property, plant and equipment	426,493	404,039
Pension and postretirement	48,355	39,110
Purchased gas adjustment	20,441	34,618
Environmental compliance	17,260	16,221
Cost recovery mechanisms	19,245	22,604
Legal and environmental contingencies	6,300	5,902
Other	19,931	33,947
Total deferred tax liabilities	558,025	556,441
Valuation allowance	1,008	1,010
Net deferred income tax liability	$ 441,320	$ 452,336