Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenues:
Total revenues	$ 483	$ 3,834	$ 972	$ 8,034
Operating expenses:
Research and development	18,007	19,201	34,772	32,628
General and administrative	3,664	5,814	8,767	9,458
Total operating expenses	21,671	25,015	43,539	42,086
Loss from operations	(21,188)	(21,181)	(42,567)	(34,052)
Other income (expense):
Interest and other income	180	151	372	351
Interest and other expense	(90)	(7)	(114)	(16)
Loss from valuation of convertible note payable	0	0	0	(1,811)
Loss before income taxes	(21,098)	(21,037)	(42,309)	(35,528)
Income tax benefit	8	2	13	6
Net loss	(21,090)	(21,035)	(42,296)	(35,522)
Other comprehensive loss:
Unrealized gain (loss) on short-term investments, net	9	(2)	50	55
Comprehensive loss	$ (21,081)	$ (21,037)	$ (42,246)	$ (35,467)
Net loss per share, basic and diluted (in dollars per share)	$ (0.40)	$ (0.41)	$ (0.80)	$ (0.70)
Weighted average shares used to compute basic and diluted net loss per share (in shares)	52,782,643	51,073,488	52,746,657	50,575,096
Strategic Alliances and Collaborations
Revenues:
Total revenues	$ 483	$ 3,834	$ 972	$ 8,034