Property and equipment, net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property Plant And Equipment [Line Items]
Depreciation and amortization expense	$ 3,700	$ 2,300	$ 900
Property and equipment, gross	89,435	$ 19,141
Construction In Progress 60 Binney Street [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 62,100