Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues:
Total revenues	$ 18	$ 204	$ 54	$ 1,176
Operating expenses:
Research and development	12,697	14,554	42,727	49,326
General and administrative	2,736	4,842	13,752	13,609
Total operating expenses	15,433	19,396	56,479	62,935
Loss from operations	(15,415)	(19,192)	(56,425)	(61,759)
Other income (expense):
Interest and other income	160	237	559	608
Interest and other expense	(580)	(560)	(1,730)	(674)
Loss before income taxes	(15,835)	(19,515)	(57,596)	(61,825)
Income tax benefit (expense)	7	(4)	139	9
Net loss	(15,828)	(19,519)	(57,457)	(61,816)
Other comprehensive loss:
Unrealized (loss) gain on short-term investments, net	(16)	(30)	19	20
Comprehensive loss	$ (15,844)	$ (19,549)	$ (57,438)	$ (61,796)
Net loss per share, basic and diluted (in dollars per share)	$ (0.18)	$ (0.37)	$ (0.88)	$ (1.17)
Weighted average shares used to compute basic and diluted net loss per share (in shares)	90,072,045	52,835,414	65,550,749	52,776,459
Strategic Alliances and Collaborations
Revenues:
Total revenues	$ 18	$ 204	$ 54	$ 1,176