Property and equipment, net - Summary of Property and Equipment Net (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 190,982	$ 169,399
Less accumulated depreciation and amortization	(10,563)	(12,444)
Total Property and equipment, net	180,419	156,955
Building [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	160,403
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	4,904	1,655
Office Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	4,188	1,427
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	20,946	16,305
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	65	13,697
Construction in Progress [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 476	$ 136,315