Subsequent Events - Narrative (Details) $ in Millions		9 Months Ended
	Oct. 31, 2024 USD ($)	Sep. 30, 2024 USD ($)	Nov. 21, 2024 USD ($)	Dec. 31, 2023 USD ($)
Letter of credit
Subsequent Event [Line Items]
Letters of credit, term		12 months
Maximum borrowing capacity		$ 2.2		$ 0.2
Subsequent event
Subsequent Event [Line Items]
Transition services agreement period	20 months
Proceeds from debt	$ 332.1
Debt issuance costs	7.9
Repayments of debt and payment of dividends	290.0
Cash retained from debt agreement	$ 42.1
Subsequent event | MDU Resources
Subsequent Event [Line Items]
Common stock distribution ratio	0.25
Subsequent event | MDU Resources
Subsequent Event [Line Items]
Payments of dividends	$ 60.0
Subsequent event | Centennial
Subsequent Event [Line Items]
Debt repayment	$ 230.0
Subsequent event | Line of credit | Senior secured credit agreement
Subsequent Event [Line Items]
Letters of credit, term	5 years
Maximum borrowing capacity	$ 525.0
Subsequent event | Term loan | Line of credit | Senior secured credit agreement
Subsequent Event [Line Items]
Face amount	300.0
Subsequent event | Revolving credit facility | Line of credit | Senior secured credit agreement
Subsequent Event [Line Items]
Maximum borrowing capacity	225.0
Outstanding balance	40.0		$ 40.0
Subsequent event | Letter of credit | Line of credit | Senior secured credit agreement
Subsequent Event [Line Items]
Maximum borrowing capacity	$ 50.0