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Warranties (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Product Warranty Disclosure [Abstract]    
Warranty, Beginning Balance $ 391 $ 246
Warranty (payments) or credits (22) (37)
Warranty additions 1 182
Warranty, Ending Balance $ 370 $ 391