Supplemental cash flow information (Schedule of Supplemental cash flow) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Supplemental Cash Flow Information [Abstract]
Interest paid, net of interest capitalized	$ 16,387	$ 16,524
Interest received	635	1,265
Net income taxes paid	43,249	13,850
Non-cash purchase of property, plant and equipment under capital lease	4,568	5,930
Non-cash right of use assets obtained (reassessed) in exchange for new lease obligations	$ 9,451	$ (139)