Supplemental Cash Flow Information (Schedule of Supplemental Cash Flow) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Supplemental Cash Flow Information [Abstract]
Interest paid, net of interest capitalized	$ 36,278	$ 20,233
Interest received	2,009	2,460
Net income taxes paid	7,902	28,037
Non-cash purchase of property, plant and equipment under capital lease	$ 5,490	$ 6,851