Changes in accumulated other comprehensive loss by component (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
Beginning Balance			$ (18.4)
Amount reclassified
Ending Balance	$ (18.4)		(18.4)
Foreign currency translation
AOCI Attributable to Parent, Net of Tax
Beginning Balance	(138.9)	$ (146.3)	(134.3)	$ (148.3)
Other comprehensive income (loss):
Foreign currency translation adjustments	(2.9)	4.7	(7.5)	6.7
Amount reclassified
Ending Balance	(141.8)	(141.6)	(141.8)	(141.6)
Accumulated other comprehensive loss, tax impacts related to rate changes	0.0	0.0	0.0	0.0
Pension
AOCI Attributable to Parent, Net of Tax
Beginning Balance	(1.6)	(0.8)	(1.6)	(0.9)
Other comprehensive income (loss):
Curtailment gain				0.1
Total Other comprehensive (loss) income before reclassifications, net of tax				0.1
Amount reclassified
Total other comprehensive income				0.1
Ending Balance	(1.6)	(0.8)	(1.6)	(0.8)
Cash flow hedges
AOCI Attributable to Parent, Net of Tax
Beginning Balance	1.4	0.8	1.1	0.7
Other comprehensive income (loss):
Net change from periodic revaluations		(0.2)	0.4	(0.5)
Tax benefit (expense)		0.1	(0.2)	0.2
Total Other comprehensive (loss) income before reclassifications, net of tax		(0.1)	0.2	(0.3)
Amount reclassified
Total other comprehensive income	0.1		0.4	0.1
Ending Balance	1.5	0.8	1.5	0.8
Amount reclassified from accumulated other comprehensive income | Foreign currency translation
Amount reclassified
Amounts reclassified to earnings, foreign currency	0.0	0.0	0.0	0.0
Amount reclassified from accumulated other comprehensive income | Cash flow hedges
Amount reclassified
Tax expense		(0.1)	(0.1)	(0.3)
Total amount reclassified from accumulated other comprehensive income (loss), net of tax	0.1	0.1	0.2	0.4
Interest rate swaps | Amount reclassified from accumulated other comprehensive income | Cash flow hedges
Amount reclassified
Interest rate swaps	$ (0.1)	$ (0.2)	$ (0.3)	$ (0.7)