Segmented information (Geographic Information of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 389,050	$ 393,222	$ 662,305	$ 696,651
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	204,588	212,233	395,118	395,806
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	97,990	90,410	133,633	121,940
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	47,430	47,283	73,768	102,068
Other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 39,042	$ 43,296	$ 59,786	$ 76,837