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Inventories (Summary of Activity within the Reserve for Excess, Obsolete, and Slow Moving Inventory) (Details) - USD ($) $ in Thousands | 12 Months Ended
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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

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