Supplemental Accumulated Other Comprehensive Loss Information - Changes in Accumulated Other Comprehensive Loss, by Component (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)
Accumulated Comprehensive Income [Roll Forward]
Beginning balance	$ 639.9
Other comprehensive income	(0.2)
Ending balance	507.4
Benefit Plans
Accumulated Comprehensive Income [Roll Forward]
Beginning balance	(4.8)
Other comprehensive income	0.0
Ending balance	(4.8)
Currency Translation Adjustments
Accumulated Comprehensive Income [Roll Forward]
Beginning balance	(14.2)
Other comprehensive income	(0.2)
Ending balance	(14.4)
Total
Accumulated Comprehensive Income [Roll Forward]
Beginning balance	(19.0)
Ending balance	$ (19.2)