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Industry, Geographic and Revenue Disaggregation - Narrative (Details)
$ in Thousands
3 Months Ended
Mar. 31, 2019
USD ($)
segment
Mar. 31, 2018
USD ($)
Dec. 31, 2018
USD ($)
Segment Reporting [Abstract]      
Number of operating segments | segment 1    
Segment Reporting Information [Line Items]      
Trade accounts receivable $ 1,950   $ 1,860
Lease Income $ 200 $ 0  
Geographic concentration | Foreign | Total revenue      
Segment Reporting Information [Line Items]      
Risk concentration 33.00% 26.00%  
Geographic concentration | Foreign | Net accounts receivable      
Segment Reporting Information [Line Items]      
Trade accounts receivable $ 1,200   $ 900