Certain Balance Sheet Accounts - Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total cost	$ 9,792		$ 9,864
Less accumulated depreciation and amortization	(6,437)		(6,035)
Total property and equipment, net	3,355		3,829
Depreciation and amortization	402	$ 377
Finance leases
Property, Plant and Equipment [Line Items]
Total cost	5,496		5,474
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total cost	2,750		2,844
Computer equipment
Property, Plant and Equipment [Line Items]
Total cost	921		921
Office equipment and furniture
Property, Plant and Equipment [Line Items]
Total cost	$ 625		$ 625