Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statements of Operations
Collaboration revenue	$ 51,505	$ 41,259
Operating expenses:
Research and development	131,012	88,385	$ 33,215
General and administrative	44,021	33,387	14,210
Total operating expenses	175,033	121,772	47,425
Income (loss) from operations	(123,528)	(80,513)	(47,425)
Interest income (expense)	971	217	(1,454)
Loss on extinguishment of debt			(1,091)
Other income (loss)	53		(1,175)
Loss before income tax provision	(122,504)	(80,296)	(51,145)
Income tax (benefit) provision	(16,787)	36,476
Net loss	(105,717)	(116,772)	(51,145)
Add: accretion of preferred stock dividends			(5,891)
Net loss attributable to common stockholders	$ (105,717)	$ (116,772)	$ (57,036)
Net loss per common share:
Basic and diluted (in dollars per share)	$ (3.06)	$ (3.51)	$ (6.34)
Weighted average common shares outstanding:
Basic and diluted (in shares)	34,580	33,258	9,003