Revenue Recognition - Disaggregated Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregated revenue	$ 1,240	$ 2,014	$ 3,091	$ 4,202
Product revenue
Disaggregated revenue	0	0	199	0
Royalty revenue
Disaggregated revenue	0	0	0	11
Contract revenue
Disaggregated revenue	1,240	2,014	2,892	4,191
Transferred at Point in Time
Disaggregated revenue	36	57	251	167
Transferred at Point in Time | Product revenue
Disaggregated revenue	0	0	199	0
Transferred at Point in Time | Royalty revenue
Disaggregated revenue	0	0	0	11
Transferred at Point in Time | Contract revenue
Disaggregated revenue	36	57	52	156
Transferred over Time
Disaggregated revenue	1,204	1,957	2,840	4,035
Transferred over Time | Product revenue
Disaggregated revenue	0	0	0	0
Transferred over Time | Royalty revenue
Disaggregated revenue	0	0	0	0
Transferred over Time | Contract revenue
Disaggregated revenue	$ 1,204	$ 1,957	$ 2,840	$ 4,035