Supplemental cash flow information (Schedule of Supplemental cash flow) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Supplemental cash flow information
Interest paid, net of interest capitalized	$ 15,171	$ 16,521
Interest received	778	855
Net income taxes paid	12,442	6,339
Non-cash purchase of property, plant and equipment under capital lease	3,502	2,564
Non-cash right of use assets obtained (reassessed) in exchange for new lease obligations	$ (1,001)	$ 784