Changes in accumulated other comprehensive loss by component (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax
Beginning Balance			$ 64.6
Amount reclassified
Ending Balance	$ 24.7		24.7
Cash flow hedges
AOCI Attributable to Parent, Net of Tax
Beginning Balance	0.8	$ (0.1)	0.7	$ 0.2
Other comprehensive loss:
Net change from periodic revaluations	(0.1)	0.1	(0.6)	(1.0)
Tax benefit (expense)	0.1	(0.1)	0.3	0.4
Total other comprehensive (loss) income before reclassifications, net of tax			(0.3)	(0.6)
Amount reclassified
Total other comprehensive loss) income	0.1	0.2	0.2	(0.1)
Ending Balance	0.9	0.1	0.9	0.1
Foreign currency translation
AOCI Attributable to Parent, Net of Tax
Beginning Balance	(141.6)	(119.7)	(148.3)	(139.1)
Other comprehensive loss:
Foreign currency translation adjustments	9.2	(22.0)	15.9	(2.6)
Amount reclassified
Ending Balance	(132.4)	(141.7)	(132.4)	(141.7)
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	(0.8)	(0.4)	(0.9)	(0.4)
Other comprehensive loss:
Curtailment gain			0.1
Total other comprehensive (loss) income before reclassifications, net of tax			0.1
Amount reclassified
Total other comprehensive loss) income			0.1
Ending Balance	(0.8)	(0.4)	(0.8)	(0.4)
Amount reclassified from accumulated other comprehensive income | Cash flow hedges
Amount reclassified
Tax expense.	(0.1)	(0.1)	(0.4)	(0.4)
Total amount reclassified from accumulated other comprehensive loss, net of tax	0.1	0.2	0.5	0.5
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
Interest rate swaps | Amount reclassified from accumulated other comprehensive income | Cash flow hedges
Amount reclassified
Amount reclassified from AOCI	$ (0.2)	$ (0.3)	$ (0.9)	$ (0.9)