Nature of Expenses Allocated by Function - Research and Development (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Income Statements, Captions [Line Items]
Personnel expenses	$ (332,353)	$ (246,171)	$ (189,418)
Personnel expense excluding equity awards compensation expense and research tax credit	(220,317)	(170,079)	(128,737)
Equity awards compensation expense	(43,259)	(23,989)	(19,600)
Research tax credit	4,941	3,386	5,063
Total research and development expenses	(123,649)	(86,807)	(60,075)
Research and Development Expense
Condensed Income Statements, Captions [Line Items]
Personnel expenses	(86,389)	(58,075)	(40,075)
Personnel expense excluding equity awards compensation expense and research tax credit	(79,222)	(54,941)	(41,456)
Equity awards compensation expense	(12,108)	(6,520)	(3,682)
Research tax credit	4,941	3,386	5,063
Other cash operating expenses	(29,867)	(21,081)	(14,888)
Subcontracting and other headcount related costs	(14,713)	(12,592)	(8,218)
Rent and facilities costs	(10,939)	(7,107)	(5,765)
Consulting and professional fees	(2,423)	(1,201)	(765)
Marketing costs	(953)	(161)	(97)
Other	(839)	(20)	(43)
Other non-cash operating expenses	(7,393)	(7,651)	(5,112)
Depreciation and amortization	(7,211)	(7,995)	(4,949)
Net change in other provisions	$ (182)	$ 344	$ (163)