Comprehensive Income - Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance (deficit)	$ 381.9	$ 377.0	$ 368.6	$ 345.2	$ 368.6	$ 313.1
Change in other comprehensive loss	(0.2)		0.2	0.1	(0.9)	(0.4)
Ending Balance (deficit)	378.3	381.9	377.0	358.7	378.3	358.7
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance (deficit)	(2.3)	(2.2)	(2.4)		(2.4)
Change in other comprehensive loss	(0.1)	(0.1)	0.2
Ending Balance (deficit)	(2.4)	(2.3)	(2.2)		(2.4)
Effective Portion of Unrealized Loss on Cash Flow Hedge
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance (deficit)	(0.8)	0.0	0.0		0.0
Change in other comprehensive loss	(0.1)	(0.8)	0.0
Ending Balance (deficit)	(0.9)	(0.8)	0.0		(0.9)
Total Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance (deficit)	(3.1)	(2.2)	(2.4)	(1.8)	(2.4)	(1.2)
Change in other comprehensive loss	(0.2)	(0.9)
Ending Balance (deficit)	$ (3.3)	$ (3.1)	$ (2.2)	$ (1.6)	$ (3.3)	$ (1.6)