Stockholders' Equity - Changes in Each Component of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance				$ (76.9)
Net current-period other comprehensive (loss) income		$ (3.3)	$ 5.1	(0.4)	$ 6.5
Ending balance		(77.3)		(77.3)
Actuarial Losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	(75.3)	(78.8)	(75.4)	(79.0)
Other comprehensive (loss) income before reclassifications	[1]	1.1	(0.6)	0.4	(0.9)
Amounts reclassified from accumulated other comprehensive loss	[1]	0.6	0.5	1.4	1.0
Net current-period other comprehensive (loss) income	[1]	1.7	(0.1)	1.8	0.1
Ending balance	[1]	(73.6)	(78.9)	(73.6)	(78.9)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	(0.5)	(11.8)	(2.5)	(13.0)
Other comprehensive (loss) income before reclassifications	[1]	(5.2)	5.0	(3.2)	6.2
Amounts reclassified from accumulated other comprehensive loss	[1]	0.0	0.0	0.0	0.0
Net current-period other comprehensive (loss) income	[1]	(5.2)	5.0	(3.2)	6.2
Ending balance	[1]	(5.7)	(6.8)	(5.7)	(6.8)
Unrealized Gain on Derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	1.8	0.0	1.0	0.0
Other comprehensive (loss) income before reclassifications	[1]	0.3	0.2	1.1	0.2
Amounts reclassified from accumulated other comprehensive loss	[1]	(0.1)	0.0	(0.1)	0.0
Net current-period other comprehensive (loss) income	[1]	0.2	0.2	1.0	0.2
Ending balance	[1]	2.0	0.2	2.0	0.2
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	(74.0)	(90.6)	(76.9)	(92.0)
Other comprehensive (loss) income before reclassifications	[1]	(3.8)	4.6	(1.7)	5.5
Amounts reclassified from accumulated other comprehensive loss	[1]	0.5	0.5	1.3	1.0
Net current-period other comprehensive (loss) income	[1]	(3.3)	5.1	(0.4)	6.5
Ending balance	[1]	$ (77.3)	$ (85.5)	$ (77.3)	$ (85.5)

[1] Amounts in parentheses indicate losses.