Regulatory Assets and Liabilities - Schedule of Unamortized Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Regulatory Asset [Abstract]
Current regulatory assets	$ 215,436	$ 172,492
Regulatory assets	322,350	447,099
Total regulatory assets	537,786	619,591
Regulatory Liability [Abstract]
Regulatory liabilities due within one year	137,167	70,761
Regulatory liabilities	459,170	521,050
Total regulatory liabilities	596,337	591,811
Net regulatory position	$ (58,551)	27,780
Environmental compliance programs
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 72,387	0
Regulatory liabilities	$ 0	61,941
Natural gas costs refundable through rate adjustments
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 45,427	43,161
Margin sharing
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 4,156	5,243
Provision for rate refund
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 3,677	6,866
Taxes refundable to customers
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 2,163	2,149
Regulatory liabilities	$ 185,402	193,578
Conservation programs
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 2,082	2,130
Cost recovery mechanisms
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	17 years
Regulatory liabilities due within one year	$ 1,720	6,284
Regulatory liabilities	$ 30,354	21,791
Cost recovery mechanisms | Maximum
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Other
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	13 years
Regulatory liabilities due within one year	$ 5,555	4,928
Regulatory liabilities	$ 2,161	1,809
Other | Maximum
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Plant removal and decommissioning costs
Regulatory Liability [Abstract]
Regulatory liabilities	$ 217,603	220,147
Accumulated deferred investment tax credit
Regulatory Liability [Abstract]
Regulatory liabilities	18,788	15,740
Pension and postretirement benefits
Regulatory Liability [Abstract]
Regulatory liabilities	4,862	6,044
Natural gas costs recoverable through rate adjustments
Regulatory Asset [Abstract]
Current regulatory assets	91,091	98,844
Regulatory assets	$ 0	55,493
Natural gas costs recoverable through rate adjustments | Minimum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Natural gas costs recoverable through rate adjustments | Maximum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	2 years
Environmental compliance programs
Regulatory Asset [Abstract]
Current regulatory assets	$ 76,964	5,525
Regulatory assets	$ 0	66,806
Environmental compliance programs | Minimum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Conservation programs
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Current regulatory assets	$ 19,123	14,425
Electric fuel and purchased power deferral
Regulatory Asset [Abstract]
Current regulatory assets	9,662	33,918
Regulatory assets	$ 4,349	0
Electric fuel and purchased power deferral | Minimum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Electric fuel and purchased power deferral | Maximum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	2 years
Decoupling mechanisms
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Current regulatory assets	$ 6,767	0
Cost recovery mechanisms
Regulatory Asset [Abstract]
Current regulatory assets	5,114	9,153
Regulatory assets	$ 76,542	85,944
Cost recovery mechanisms | Minimum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Cost recovery mechanisms | Maximum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	24 years
Other
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	14 years
Current regulatory assets	$ 6,715	10,627
Regulatory assets	$ 5,990	6,614
Other | Minimum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Pension and postretirement benefits
Regulatory Asset [Abstract]
Regulatory assets	$ 142,064	142,511
Plant costs/asset retirement obligations
Regulatory Asset [Abstract]
Regulatory assets	47,042	46,009
Manufactured gas plant site remediation
Regulatory Asset [Abstract]
Regulatory assets	27,964	26,127
Taxes refundable to customers
Regulatory Asset [Abstract]
Regulatory assets	12,221	12,249
Covid-19 deferred costs
Regulatory Asset [Abstract]
Regulatory assets	$ 4,167	2,746
Long-term debt refinancing costs
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	36 years
Regulatory assets	$ 2,011	$ 2,600