Segmented information (Geographic Information of Revenue and location of assets) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 383,413	$ 331,542	$ 389,050	$ 273,255	$ 332,194	$ 289,796	$ 393,222	$ 303,429	$ 355,972	$ 245,346	$ 308,530	$ 260,178	$ 1,377,260	$ 1,318,641	$ 1,170,026
Property, plant and equipment	492,127				484,482								492,127	484,482
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue													754,815	743,793	548,695
Property, plant and equipment	252,335				256,159								252,335	256,159
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue													305,236	247,737	284,989
Property, plant and equipment	106,973				106,922								106,973	106,922
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue													158,999	173,054	180,817
Property, plant and equipment	83,014				73,991								83,014	73,991
Other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue													158,210	154,057	$ 155,525
Property, plant and equipment	$ 49,805				$ 47,410								$ 49,805	$ 47,410