Condensed Statements of Operations and Comprehensive Loss (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues:
Total revenues	$ 1,083	$ 6,118	$ 3,450	$ 14,115
Operating expenses:
Research and development	10,173	7,106	30,572	21,710
General and administrative	2,569	1,917	8,255	5,545
Total operating expenses	12,742	9,023	38,827	27,255
Loss from operations	(11,659)	(2,905)	(35,377)	(13,140)
Other income (expense):
Interest and other income	86	72	283	207
Interest expense	(10)	(7)	(31)	(25)
Gain (loss) from valuation of convertible note payable	1,785	671	614	(3,787)
Loss before income taxes	(9,798)	(2,169)	(34,511)	(16,745)
Income tax (benefit) expense		(5)	1	(4)
Net loss	(9,798)	(2,164)	(34,512)	(16,741)
Other comprehensive loss:
Unrealized (loss) gain on short-term investments, net	(24)	37	(50)	8
Comprehensive loss	(9,822)	(2,127)	(34,562)	(16,733)
Net loss per share:
Basic	$ (0.23)	$ (0.05)	$ (0.80)	$ (0.45)
Diluted	$ (0.26)	$ (0.07)	$ (0.80)	$ (0.45)
Weighted average shares used to compute net loss per share:
Basic	43,406,251	40,154,812	43,155,601	37,367,368
Diluted	44,855,463	41,555,660	43,155,601	37,367,368
Strategic Alliances and Collaborations
Revenues:
Total revenues	$ 1,083	$ 6,118	$ 3,450	$ 14,115