Income Taxes - Schedule of Income Tax Expense (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Current Income Tax Expense
Federal		$ 10.1	$ 3.7	$ 14.7
State		13.9	2.7	5.5
Other		(0.5)	(0.4)	0.0
Total current income tax expense		23.5	6.0	20.2
Deferred Income Tax Expense
Total deferred income tax expense	[1]	29.2	37.2	7.9
Total Income Tax Expense		52.7	43.2	28.1
Property, plant and equipment
Deferred Income Tax Expense
Total deferred income tax expense		29.4	29.3	7.8
Deferred gas costs
Deferred Income Tax Expense
Total deferred income tax expense		$ (0.2)	$ 7.9	$ 0.1

[1] .