Inventories (Summary of Activity within the Reserve for Excess, Obsolete, and Slow Moving Inventory) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Inventory [Roll Forward]
Beginning balance	$ 3,801	$ 7,428	$ 5,575
Excess, obsolete and slow moving inventory expense	1,276	(239)	1,539
Scrapped inventory and other adjustments	(1,382)	(3,388)	314
Ending balance	$ 3,695	$ 3,801	$ 7,428