Segment and geographic information - Geographic (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Revenue and Assets
Revenue	$ 98.2	$ 103.1	$ 204.6	$ 214.4
Property, Plant and Equipment, net of accumulated depreciation	768.1		768.1		$ 777.7
United States
Revenue and Assets
Revenue	59.4	65.4	118.1	126.2
Property, Plant and Equipment, net of accumulated depreciation	510.5		510.5		529.6
Canada
Revenue and Assets
Revenue	38.8	$ 37.7	86.5	$ 88.2
Property, Plant and Equipment, net of accumulated depreciation	$ 257.6		$ 257.6		$ 248.1