Property and equipment, net - Property and equipment, net (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Property and equipment, net
Property and Equipment, gross	$ 346,051	$ 334,427
Less accumulated depreciation and amortization	(81,441)	(74,664)
Property and Equipment, net	264,610	259,763	[1]
Office equipment
Property and equipment, net
Property and Equipment, gross	15,978	14,674
Laboratory equipment
Property and equipment, net
Property and Equipment, gross	54,434	48,807
Computer equipment
Property and equipment, net
Property and Equipment, gross	51,876	51,351
Land
Property and equipment, net
Property and Equipment, gross	5,350	5,350
Building and leasehold improvements
Property and equipment, net
Property and Equipment, gross	$ 218,413	$ 214,245

[1] The condensed consolidated balance sheet at December 31, 2017 has been derived from the audited financial statements at that date.