Intangible Assets - Gross Carrying Amount (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Gross Carrying Amount	$ 6,261	$ 5,520
Accumulated amortization	(2,203)	(1,735)
Total	4,058	$ 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	$ 5,941	$ 5,200
Accumulated amortization	(2,032)	(1,593)
Total	$ 3,909	$ 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	(117)	(97)
Total	$ 143	$ 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	(54)	(45)
Total	$ 6	$ 15