Stockholders' Equity - Reclassifications from Accumulated Other Comprehensive Loss (Details) - Amount Reclassified from Accumulated Other Comprehensive Loss - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial losses of defined benefit pension plans	[1]	$ (1.0)	$ (1.0)	$ (2.8)	$ (2.5)
Amortization of prior service costs of defined benefit pension plans	[1]	0.0	0.0	(0.1)	(0.1)
Interest rate swaps	[1]	(0.2)	0.2	(0.2)	0.9
Total before tax	[1]	(1.2)	(0.8)	(3.1)	(1.7)
Income tax benefit	[1]	0.4	0.2	0.8	0.3
Total reclassifications for the period, net of tax	[1]	$ (0.8)	$ (0.6)	$ (2.3)	$ (1.4)

[1] Amounts in parentheses indicate losses.