Supplemental Cash Flow Information (Schedule of Supplemental Cash Flow) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Information
Interest paid, net of interest capitalized	$ 37,046	$ 39,429	$ 23,360
Interest received	3,802	2,888	3,196
Net income taxes paid	26,699	10,352	28,281
Non-cash purchase of property, plant and equipment under capital lease	15,282	$ 8,968	$ 8,820
Non-cash right of use assets obtained in exchange for new lease obligations	$ 29,117