Restructuring charges - Costs Incurred and Anticipated (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 2.5	$ 0.1
2018 Plan
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.2
Cumulative costs	7.0
Anticipated total costs	7.0
2018 Plan | USA
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.1
Cumulative costs	5.7
Anticipated total costs	5.7
2018 Plan | Non-US
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.1
Cumulative costs	1.3
Anticipated total costs	1.3
2018 Plan | Employee termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.2
Cumulative costs	6.9
Anticipated total costs	6.9
2018 Plan | Employee termination costs | USA
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.1
Cumulative costs	5.6
Anticipated total costs	5.6
2018 Plan | Other exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0
Cumulative costs	0.1
Anticipated total costs	0.1
2018 Plan | Other exit costs | USA
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0
Cumulative costs	0.1
Anticipated total costs	$ 0.1