Accumulated Other Comprehensive Loss - Changes in accumulated other comprehensive loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments for losses included in net income, net of tax expense (benefit)	$ 0.0	$ (3.0)	$ 0.0
AOCI Attributable to Parent
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(17.7)	(19.8)	(18.4)
Other comprehensive income (loss), net of tax, before reclassifications	(2.3)	(0.9)	(1.4)
Reclassification adjustments for losses included in net income, net of tax expense (benefit)	(0.3)	(3.0)
Other comprehensive income (loss)	(2.0)	2.1	(1.4)
Ending balance	(19.7)	(17.7)	(19.8)
Currency translation adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(16.8)	(19.8)	(18.4)
Other comprehensive income (loss), net of tax, before reclassifications	0.5	0.0	(1.4)
Reclassification adjustments for losses included in net income, net of tax expense (benefit)	0.0	(3.0)
Other comprehensive income (loss)	0.5	3.0	(1.4)
Ending balance	(16.3)	(16.8)	(19.8)
Unrealized loss on derivative financial instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(0.9)	0.0	0.0
Other comprehensive income (loss), net of tax, before reclassifications	(2.8)	(0.9)	0.0
Reclassification adjustments for losses included in net income, net of tax expense (benefit)	0.3	0.0
Other comprehensive income (loss)	(2.5)	(0.9)	0.0
Ending balance	$ (3.4)	$ (0.9)	$ 0.0