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Summary of Significant Accounting Policies (Inventory) (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 USD ($) compressor | Dec. 31, 2017 USD ($)
Accounting Policies [Abstract] |  |
Inventory valuation reserves, deductions | $ 19 | $ 15
Available-for-sale or rental, compressor units | compressor | 7 |
Raw materials -current | $ 26,152 | 22,813
Raw materials - long term | 3,980 | 2,829
Finished Goods | 1,022 | 1,022
Work in process | 3,800 | 2,389
Inventory | $ 34,954 | $ 29,053

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