Segment information - Assets, Long Lived Assets, Revenues, Net Assets by Geographic Area (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Assets held by Reportable Segment	$ 3,236.0				$ 3,059.6				$ 3,236.0	$ 3,059.6	$ 1,994.8
Long-Lived Assets by Geographic Area	699.4				640.9				699.4	640.9	531.0
Revenues	907.7	$ 852.4	$ 849.7	$ 879.1	903.2	$ 849.5	$ 805.9	$ 788.4	3,488.9	3,347.0	3,020.6
Net assets outside the U.S.	1,141.5				1,191.0				1,141.5	1,191.0	684.1
Reportable Segments:
Segment Reporting Information [Line Items]
Assets held by Reportable Segment	2,947.7				2,357.3				2,947.7	2,357.3	1,622.6
Revenues									3,437.5	3,192.9	2,908.4
Corporate items
Segment Reporting Information [Line Items]
Assets held by Reportable Segment	288.3				643.6				288.3	643.6	321.3
North America | Reportable Segments:
Segment Reporting Information [Line Items]
Assets held by Reportable Segment	1,404.5				733.5				1,404.5	733.5	629.4
Revenues									1,466.3	1,254.2	1,210.3
South America | Reportable Segments:
Segment Reporting Information [Line Items]
Assets held by Reportable Segment	602.5				740.5				602.5	740.5	371.4
Revenues									926.9	924.6	718.7
Rest of World | Reportable Segments:
Segment Reporting Information [Line Items]
Assets held by Reportable Segment	940.7				883.3				940.7	883.3	621.8
Revenues									1,044.3	1,014.1	979.4
Mexico
Segment Reporting Information [Line Items]
Long-Lived Assets by Geographic Area	107.0				99.6				107.0	99.6	78.1
Revenues									365.3	327.2	296.3
Net assets outside the U.S.	154.8				133.7				154.8	133.7	86.1
France
Segment Reporting Information [Line Items]
Long-Lived Assets by Geographic Area	79.0				84.1				79.0	84.1	67.5
Revenues									428.5	429.4	424.5
Net assets outside the U.S.	213.4				219.4				213.4	219.4	102.1
Brazil
Segment Reporting Information [Line Items]
Long-Lived Assets by Geographic Area	62.5				57.2				62.5	57.2	45.3
Revenues									405.4	434.6	344.9
Net assets outside the U.S.	147.9				151.3				147.9	151.3	106.3
ARGENTINA
Segment Reporting Information [Line Items]
Revenues									247.2	250.3	156.4
Net assets outside the U.S.	154.6				234.0				154.6	234.0	28.6
Venezuela
Segment Reporting Information [Line Items]
Revenues									51.4	154.1	109.4
Venezuela | Other items not allocated to segments:
Segment Reporting Information [Line Items]
Assets held by Reportable Segment	0.0				58.7				0.0	58.7	50.9
Revenues									51.4	154.1	109.4
Canada
Segment Reporting Information [Line Items]
Long-Lived Assets by Geographic Area	47.6				46.7				47.6	46.7	42.4
Revenues									151.7	151.2	150.2
Net assets outside the U.S.	52.0				63.3				52.0	63.3	57.6
Other
Segment Reporting Information [Line Items]
Long-Lived Assets by Geographic Area	135.4				146.5				135.4	146.5	127.2
Revenues									890.1	824.4	775.1
Subtotal
Segment Reporting Information [Line Items]
Long-Lived Assets by Geographic Area	431.5				434.1				431.5	434.1	360.5
Revenues									2,539.6	2,571.2	2,256.8
U.S.
Segment Reporting Information [Line Items]
Long-Lived Assets by Geographic Area	267.9				206.8				267.9	206.8	170.5
Revenues									949.3	775.8	763.8
Other Rest of World countries
Segment Reporting Information [Line Items]
Net assets outside the U.S.	309.2				273.1				309.2	273.1	205.0
Other South American countries
Segment Reporting Information [Line Items]
Net assets outside the U.S.	$ 109.6				$ 116.2				$ 109.6	$ 116.2	$ 98.4