Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Total revenues	$ 18	$ 18	$ 54	$ 54
Operating expenses:
Research and development	6,879	12,697	28,720	42,727
General and administrative	2,993	2,736	10,115	13,752
Total operating expenses	9,872	15,433	38,835	56,479
Loss from operations	(9,854)	(15,415)	(38,781)	(56,425)
Other income (expense):
Interest and other income	201	160	483	559
Interest and other expense	(620)	(580)	(1,848)	(1,730)
Loss before income taxes	(10,273)	(15,835)	(40,146)	(57,596)
Income tax benefit	0	7	0	139
Net loss	(10,273)	(15,828)	(40,146)	(57,457)
Other comprehensive loss:
Unrealized gain (loss) on short-term investments, net	16	(16)	70	19
Comprehensive loss	$ (10,257)	$ (15,844)	$ (40,076)	$ (57,438)
Net loss per share, basic and diluted (in dollars per share)	$ (1.18)	$ (2.11)	$ (4.62)	$ (10.52)
Weighted average shares used to compute basic and diluted net loss per share (in shares)	8,703,626	7,506,529	8,688,831	5,463,096
Revenue under strategic alliances and collaborations
Revenues:
Total revenues	$ 18	$ 18	$ 54	$ 54