Property and Equipment - Property and Equipment and Related Accumulated Depreciation and Amortization (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and Equipment, Gross	$ 61,717	$ 38,435
Less: accumulated depreciation and amortization	(24,943)	(17,420)
Property and Equipment, Net	36,774	21,015
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Gross	23,786	14,843
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Gross	9,701	6,673
Software [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Gross	3,190	2,111
Furniture and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Gross	3,376	1,974
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Gross	18,783	$ 12,834
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Gross	$ 2,881