Stockholder's Equity - Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (1.7)	$ (2.8)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			(0.8)	(0.3)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			(0.7)	(1.0)
Net current-period other comprehensive income (loss)	$ (0.4)	$ (2.5)	(1.5)	(1.3)
Ending balance	(3.2)	(4.1)	(3.2)	(4.1)
Proceeds from Issuance of Common Stock, Dividend Reinvestment Plan			76.3	56.8
Proceeds from Issuance of Common Stock, Dividend Reinvestment Plan			76.3	56.8
Maximum [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Proceeds from Stock Plans			100.0
Proceeds from Stock Plans			100.0
UnrealizedGainsLossesFromDefinedBenefitPensionAndPostretirementPlanItems [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(2.1)	(2.6)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0.0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			0.0	0.0
Net current-period other comprehensive income (loss)			0.0	0.0
Ending balance	(2.1)	(2.6)	(2.1)	(2.6)
Accumulated (Gain) Loss from Commodity Contracts Cash Flows Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			0.4	(0.3)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(0.4)	(0.6)	0.0	1.0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0.1	0.1	(0.5)	(0.6)
Net current-period other comprehensive income (loss)			(0.5)	0.4
Ending balance	(0.1)	0.1	(0.1)	0.1
Accumulated (Gain) Loss from Interest Rate Swap Cash Flows Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			0.0	0.1
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(0.1)	(1.8)	(0.8)	(1.3)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax				(0.4)
Net current-period other comprehensive income (loss)			(1.0)	(1.7)
Ending balance	$ (1.0)	$ (1.6)	$ (1.0)	$ (1.6)