Unaudited Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Collaboration revenue	$ 1,662	$ 15,721
Operating expenses:
Research and development	31,979	37,770
General and administrative	13,159	14,696
Total operating expenses	45,138	52,466
Loss from operations	(43,476)	(36,745)
Interest income	378	446
Other income (loss)	(21)	30
Loss before income tax provision	(43,119)	(36,269)
Income tax provision	3	32
Net loss	$ (43,122)	$ (36,301)
Net loss per common share:
Basic and diluted (in dollars per share)	$ (1.20)	$ (1.03)
Weighted average common shares outstanding:
Basic and diluted (in shares)	35,804	35,256