Regulatory Assets and Liabilities - Regulatory Liabilities (Details-2) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Regulatory Liability [Line Items]
Regulatory Liability	$ 177,612	$ 168,913
Non Asset Retirement Obligation Removal Cost [Member]
Regulatory Liability [Line Items]
Regulatory Liability	42,031	31,664
Elm Road [Member]
Regulatory Liability [Line Items]
Regulatory Liability	1,666	1,092
Deferred Fuel Savings [Member]
Regulatory Liability [Line Items]
Regulatory Liability	7,219	0
Income Taxes
Regulatory Liability [Line Items]
Regulatory Liability	107,048	109,112
Deferred Pension And Other Postretirement Costs [Member]
Regulatory Liability [Line Items]
Regulatory Liability	0	5,454
Pension and Other Postretirement Plans Costs [Member]
Regulatory Liability [Line Items]
Regulatory Liability	17,977	16,160
Purchased Gas Adjustment [Member]
Regulatory Liability [Line Items]
Regulatory Liability	1,340	4,857
Other Regulatory Liability [Member]
Regulatory Liability [Line Items]
Regulatory Liability	$ 331	$ 574