Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities	$ (28,842)	$ 39,957	$ (7,034)
Regulatory Assets [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets	804,265	773,571
Regulatory Assets [Member] | Flow-through income taxes
Regulatory Assets And Liabilities [Line Items]
Regulatory assets	596,265	553,452
Regulatory Assets [Member] | Pension
Regulatory Assets And Liabilities [Line Items]
Regulatory assets	62,096	79,638
Regulatory Assets [Member] | Excess deferred income taxes
Regulatory Assets And Liabilities [Line Items]
Regulatory assets	45,620	51,404
Regulatory Assets [Member] | Employee related benefits
Regulatory Assets And Liabilities [Line Items]
Regulatory assets	17,877	21,926
Regulatory Assets [Member] | Deferred financing costs
Regulatory Assets And Liabilities [Line Items]
Regulatory assets	17,754	20,028
Regulatory Assets [Member] | Wildfire mitigation
Regulatory Assets And Liabilities [Line Items]
Regulatory assets	17,368	1,623
Regulatory Assets [Member] | Supply costs
Regulatory Assets And Liabilities [Line Items]
Regulatory assets	11,441	7,317
Regulatory Assets [Member] | Environmental clean-up
Regulatory Assets And Liabilities [Line Items]
Regulatory assets	11,257	11,131
Regulatory Assets [Member] | State & local taxes & fees
Regulatory Assets And Liabilities [Line Items]
Regulatory assets	8,924	2,733
Regulatory Assets [Member] | Other
Regulatory Assets And Liabilities [Line Items]
Regulatory assets	15,663	24,319
Regulatory Liabilities [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities	693,203	718,555
Regulatory Liabilities [Member] | Removal cost
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities	537,210	523,744
Regulatory Liabilities [Member] | Excess deferred income taxes
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities	125,878	136,382
Regulatory Liabilities [Member] | Supply costs
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities	$ 20,933	19,691
Regulatory liability, remaining amortization period	1 year
Regulatory Liabilities [Member] | Gas storage sales
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities	$ 6,205	6,625
Regulatory liability, remaining amortization period	15 years
Regulatory Liabilities [Member] | State & local taxes & fees
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities	$ 251	30,576
Regulatory liability, remaining amortization period	1 year
Regulatory Liabilities [Member] | Environmental remediation obligations [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liability, remaining amortization period	1 year
Regulatory Liabilities [Member] | Other
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities	$ 2,726	$ 1,537
Minimum [Member] | Regulatory Assets [Member] | Deferred financing costs
Regulatory Assets And Liabilities [Line Items]
Regulatory assets, remaining amortization period	1 year
Maximum [Member] | Regulatory Assets [Member] | Deferred financing costs
Regulatory Assets And Liabilities [Line Items]
Regulatory assets, remaining amortization period	23 years