Property and Equipment, Net - Components of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 20,456	$ 19,659
Less: Accumulated depreciation and amortization	(4,588)	(3,035)
Property and equipment, net	15,868	16,624
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	577	529
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	312	354
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	7,442	6,819
Office equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	400	400
Building related to facility lease obligation
Property, Plant and Equipment [Line Items]
Property and equipment, gross	10,557	10,557
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,168	$ 1,000