Quarterly report pursuant to Section 13 or 15(d)

Accrued Expenses - Schedule of Accrued Expenses (Details)

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Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Payables And Accruals [Abstract]      
Compensation and related benefits $ 574 $ 1,734  
Accrued warranty (Note 6) 193 112 $ 87
Accrued services 294 963  
Accrued expenses $ 1,061 $ 2,809