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Revenue - Disaggregated by Timing of Recognition (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Disaggregation of Revenue    
Revenue $ 37,503 $ 49,417
Point in time    
Disaggregation of Revenue    
Revenue 35,665 45,102
Over time    
Disaggregation of Revenue    
Revenue $ 1,838 $ 4,315