Supplemental Cash Flow Information (Schedule of Supplemental Cash Flow) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Supplemental Cash Flow Information [Abstract]
Interest paid, net of interest capitalized	$ 2,250	$ 2,922
Interest received	1,943	984
Net income taxes paid	23,458	36,870
Non-cash purchase of property, plant and equipment under capital lease	$ 3,483	$ 756