Facility Lease - Lease cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating lease cost
Base rent expense	$ 249	$ 177
Common area maintenance	81	75
Total operating lease cost	330	252
Other Information
Operating cash flows used for operating lease	359	$ 356
Operating lease liabilities arising from obtaining right-of-use asset	$ 3,769
Remaining lease term	3 years 9 months 18 days	2 years 9 months 18 days
Discount rate	10.00%