Intangible Assets - Gross Carrying Amount (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets    
Gross Carrying Amount $ 6,246 $ 5,520
Accumulated amortization (2,356) (1,735)
Total 3,890 $ 3,785
Milestone payments $ 2,900  
Acquired technology    
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets    
Weighted Average Amortization Period 9 years 9 years
Gross Carrying Amount $ 5,926 $ 5,200
Accumulated amortization (2,176) (1,593)
Total $ 3,750 $ 3,607
Customer relationships    
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets    
Weighted Average Amortization Period 10 years 10 years
Gross Carrying Amount $ 260 $ 260
Accumulated amortization (123) (97)
Total $ 137 $ 163
Trademark    
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets    
Weighted Average Amortization Period 5 years 5 years
Gross Carrying Amount $ 60 $ 60
Accumulated amortization (57) (45)
Total $ 3 $ 15