Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 31,697	$ 25,156
Less: Accumulated depreciation	(13,587)	(10,227)
Property and equipment, net	18,110	14,929
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	11,223	6,687
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,213	2,529
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,117	228
Equipment Acquired Under Capital Leases
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,468	6,172
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 10,676	$ 9,540