Supplemental cash flow information (Schedule of Supplemental cash flow) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Supplemental Cash Flow Information [Abstract]
Interest paid, net of interest capitalized	$ 31,173	$ 34,955
Interest received	1,775	2,491
Net income taxes paid	32,750	23,193
Non-cash purchase of property, plant and equipment under capital lease	8,431	10,747
Non-cash right of use assets obtained (reassessed) in exchange for new lease obligations	$ 595	$ 28,121