Supplemental Cash Flow Information (Schedule of Supplemental Cash Flow) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Information [Abstract]
Interest paid, net of interest capitalized	$ 39,429	$ 23,360	$ 5,792
Interest received	2,888	3,196	1,861
Net income taxes paid	10,352	28,281	54,037
Non-cash purchase of property, plant and equipment under capital lease	$ 8,968	$ 8,820	$ 3,376