Stockholders' Equity - Changes in Each Component of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ (76.9)
Net current-period other comprehensive income		2.9	$ 1.4
Ending balance		(74.0)
Actuarial Losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	(75.4)	(79.0)
Other comprehensive (loss) income before reclassifications	[1]	(0.7)	(0.3)
Amounts reclassified from accumulated other comprehensive loss	[1]	0.8	0.5
Net current-period other comprehensive income	[1]	0.1	0.2
Ending balance	[1]	(75.3)	(78.8)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	(2.5)	(13.0)
Other comprehensive (loss) income before reclassifications	[1]	2.0	1.2
Amounts reclassified from accumulated other comprehensive loss	[1]	0.0	0.0
Net current-period other comprehensive income	[1]	2.0	1.2
Ending balance	[1]	(0.5)	(11.8)
Unrealized Gain on Derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	1.0	0.0
Other comprehensive (loss) income before reclassifications	[1]	0.8	0.0
Amounts reclassified from accumulated other comprehensive loss	[1]	0.0	0.0
Net current-period other comprehensive income	[1]	0.8	0.0
Ending balance	[1]	1.8	0.0
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	(76.9)	(92.0)
Other comprehensive (loss) income before reclassifications	[1]	2.1	0.9
Amounts reclassified from accumulated other comprehensive loss	[1]	0.8	0.5
Net current-period other comprehensive income	[1]	2.9	1.4
Ending balance	[1]	$ (74.0)	$ (90.6)

[1] Amounts in parentheses indicate losses.