Condensed Statements of Operations (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Collaboration and license revenue	$ 2,766	$ 738	$ 8,474	$ 70,084
Operating expenses:
Research and development	18,088	9,954	56,642	36,004
General and administrative	3,907	2,879	10,654	8,744
Total operating expenses	21,995	12,833	67,296	44,748
Income (loss) from operations	(19,229)	(12,095)	(58,822)	25,336
Interest and other income (expense), net	679	607	532	(188)
Net income (loss)	(18,550)	(11,488)	(58,290)	25,148
Net income (loss) attributable to common stockholders:
Basic	(18,550)	(11,488)	(58,290)	322
Diluted	$ (18,550)	$ (11,488)	$ (58,290)	$ 462
Shares used to compute net income (loss) per share attributable to common stockholders:
Basic	35,200,761	1,370,190	17,218,475	1,342,919
Diluted	35,200,761	1,370,190	17,218,475	1,976,618
Net income (loss) per share attributable to common stockholders:
Basic	$ (0.53)	$ (8.38)	$ (3.39)	$ 0.24
Diluted	$ (0.53)	$ (8.38)	$ (3.39)	$ 0.23