Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenue
Collaborations, licenses and milestones	$ 3,503	$ 848	$ 6,008	$ 3,856
Operating expenses
Research and development	10,582	4,953	23,263	13,464
General and administrative	3,233	2,182	8,521	5,499
Total operating expenses	13,815	7,135	31,784	18,963
Loss from operations	(10,312)	(6,287)	(25,776)	(15,107)
Other income (expenses)
Interest income	676	2	1,067	31
Interest expense	(4)	(2)	(11)	(7)
Other income (expenses)	(397)	9	(629)	10
Total other income (expense), net	275	9	427	34
Net loss	(10,037)	(6,278)	(25,349)	(15,073)
Other comprehensive loss
Net unrealized gain (loss) on marketable securities available-for-sale	84		(6)
Comprehensive loss	$ (9,953)	$ (6,278)	$ (25,355)	$ (15,073)
Basic and diluted net loss per common share (in dollars per share)	$ (0.25)	$ (0.20)	$ (0.66)	$ (0.48)
Weighted-average common shares outstanding used in computing basic and diluted net loss (in shares)	40,473,520	31,395,626	38,514,179	31,376,502