Intangible Assets - Gross Carrying Amount (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Gross Carrying Amount	$ 6,181	$ 6,246
Accumulated amortization	(2,504)	(2,356)
Total	3,677	$ 3,890
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	$ 5,861	$ 5,926
Accumulated amortization	(2,314)	(2,176)
Total	$ 3,547	$ 3,750
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	(130)	(123)
Total	$ 130	$ 137
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	$ (60)	(57)
Total		$ 3