Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statements of Operations
Total collaboration revenue	$ 41,259
Costs and expenses:
Research and development	88,385	$ 33,215	$ 6,792
General and administrative	33,387	14,210	6,889
Total costs and expenses	121,772	47,425	13,681
Income (loss) from operations	(80,513)	(47,425)	(13,681)
Interest income (expense)	217	(1,454)	(507)
Loss on extinguishment of debt		(1,091)
Other loss		(1,175)	(374)
Income (loss) before income tax provision	(80,296)	(51,145)	(14,562)
Income tax provision	(36,476)
Net loss	(116,772)	(51,145)	(14,562)
Add: accretion of preferred stock dividends		(5,891)	(7,063)
Net income (loss) attributable to common stockholders	$ (116,772)	$ (57,036)	$ (21,625)
Net income (loss) per common stockholders per share:
Basic and diluted (in dollars per share)	$ (3.51)	$ (6.34)	$ (14.89)
Weighted average common shares outstanding:
Basic and diluted (in shares)	33,258	9,003	1,452