Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 46,391	$ 45,370
Less: Accumulated depreciation and amortization	(18,308)	(12,439)
Property and equipment, net	28,083	32,931
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	14,367	13,181
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,864	2,832
Furniture and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,033	1,033
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	27,977	27,963
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 150	$ 361

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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