Regulatory Assets and Liabilities - Schedule of Unamortized Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Regulatory Asset [Abstract]
Current regulatory assets	$ 172,492	$ 165,092
Regulatory assets	447,099	329,659
Total regulatory assets	619,591	494,751
Regulatory Liability [Abstract]
Regulatory liabilities due within one year	70,761	26,440
Regulatory liabilities	521,050	448,454
Total regulatory liabilities	591,811	474,894
Net regulatory position	$ 27,780	19,857
Natural gas costs refundable through rate adjustments
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 43,161	955
Provision for rate refund
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 6,866	1,147
Cost recovery mechanisms
Regulatory Liability [Abstract]
Regulatory liabilities due within one year	6,284	1,977
Regulatory liabilities	$ 21,791	14,025
Cost recovery mechanisms | Minimum
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Cost recovery mechanisms | Maximum
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	18 years
Margin sharing
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 5,243	0
Taxes recoverable from customers
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 2,149	3,937
Regulatory liabilities	$ 193,578	203,222
Conservation programs
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 2,130	4,126
Refundable fuel & electric costs
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 263	3,253
Electric fuel and purchased power deferral
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 0	4,929
Other
Regulatory Liability [Abstract]
Regulatory liabilities due within one year	4,665	6,116
Regulatory liabilities	$ 1,809	1,587
Other | Minimum
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Other | Maximum
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	14 years
Plant to be retired
Regulatory Liability [Abstract]
Regulatory liabilities	$ 220,147	208,650
Environmental compliance programs
Regulatory Liability [Abstract]
Regulatory liabilities	61,941	0
Accumulated deferred investment tax credit
Regulatory Liability [Abstract]
Regulatory liabilities	15,740	13,594
Pension and postretirement benefits
Regulatory Liability [Abstract]
Regulatory liabilities	6,044	7,376
Natural gas costs recoverable through rate adjustments
Regulatory Asset [Abstract]
Current regulatory assets	98,844	141,306
Regulatory assets	$ 55,493	0
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
Electric fuel and purchased power deferral
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Current regulatory assets	$ 33,918	2,656
Conservation programs
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Current regulatory assets	$ 14,425	8,544
Cost recovery mechanisms
Regulatory Asset [Abstract]
Current regulatory assets	9,153	4,019
Regulatory assets	$ 85,944	67,171
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	25 years
Environmental compliance programs
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Current regulatory assets	$ 5,525	0
Regulatory assets	66,806	0
Other
Regulatory Asset [Abstract]
Current regulatory assets	10,627	8,567
Regulatory assets	$ 8,588	11,010
Other | Minimum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Other | Maximum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	15 years
Pension and postretirement benefits
Regulatory Asset [Abstract]
Regulatory assets	$ 142,511	143,349
Plant costs/asset retirement obligations
Regulatory Asset [Abstract]
Regulatory assets	46,009	44,462
Manufactured gas plant site remediation
Regulatory Asset [Abstract]
Regulatory assets	26,127	26,624
Taxes recoverable from customers
Regulatory Asset [Abstract]
Regulatory assets	$ 12,249	12,330
Long-term debt refinancing costs
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	37 years
Regulatory assets	$ 2,600	3,188
Plant to be retired
Regulatory Asset [Abstract]
Regulatory assets	$ 772	$ 21,525