Property and equipment, net - Summary of Property and Equipment Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 196,004	$ 169,399
Less accumulated depreciation and amortization	(14,284)	(12,444)
Total Property and equipment, net	181,720	156,955
Building [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	122,451
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	5,528	1,655
Office Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	2,977	1,427
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	16,497	16,305
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	13,697	13,697
Construction in Progress [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 34,854	$ 136,315