Accumulated Other Comprehensive Loss - Changes in accumulated other comprehensive loss (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024	Dec. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity, Including Portion Attributable to Noncontrolling Interest	$ 1,250.4	$ 1,257.8	$ 1,299.7	$ 1,298.5	$ 1,304.0	$ 1,288.5	$ 1,250.4	$ 1,298.5	$ 1,307.2	$ 1,275.5
Changes in accumulated other comprehensive loss
Other comprehensive income, net of tax, before reclassifications							1.7
Amounts reclassified from AOCI, net of tax expense of $0.5, $—, and $0.5							(1.2)
Reclassification from AOCI, Current Period, Tax							0.5
Less: noncontrolling interest	(0.3)	(0.1)	(0.1)	16.9	10.9	(7.5)	(0.5)	20.3
Other comprehensive income							0.3
Unrealized gains/(losses) on derivative financial instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity, Including Portion Attributable to Noncontrolling Interest	(2.8)						(2.8)		(3.0)
Changes in accumulated other comprehensive loss
Other comprehensive income, net of tax, before reclassifications							1.7
Amounts reclassified from AOCI, net of tax expense of $0.5, $—, and $0.5							(1.3)
Reclassification from AOCI, Current Period, Tax							0.5
Other comprehensive income							0.2
Net actuarial gains/(losses) of defined benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity, Including Portion Attributable to Noncontrolling Interest	(1.1)						(1.1)		(1.2)
Changes in accumulated other comprehensive loss
Other comprehensive income, net of tax, before reclassifications							0.0
Amounts reclassified from AOCI, net of tax expense of $0.5, $—, and $0.5							0.1
Reclassification from AOCI, Current Period, Tax							0.0
Other comprehensive income							0.1
Accumulated Gain (Loss), Net, Cash Flow Hedge, Noncontrolling Interest [Member]
Changes in accumulated other comprehensive loss
Less: noncontrolling interest							(0.2)
Noncontrolling Interest [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity, Including Portion Attributable to Noncontrolling Interest	249.4	248.7	246.5	241.1	238.5	239.2	249.4	241.1	248.3	238.4
Changes in accumulated other comprehensive loss
Less: noncontrolling interest	0.0	(0.1)	(0.1)	(0.1)	(0.1)	(0.1)	(0.2)
Accumulated other comprehensive income (loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity, Including Portion Attributable to Noncontrolling Interest	(3.9)	(4.2)	(4.2)	(9.6)	7.4	18.4	$ (3.9)	$ (9.6)	$ (4.2)	$ 11.0
Changes in accumulated other comprehensive loss
Less: noncontrolling interest	$ (0.3)	$ 0.0	$ 0.0	$ 17.0	$ 11.0	$ (7.4)