CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
Revenue	$ 277	$ 114	$ 506	$ 358
Operating expenses:
Research and development	3,298	6,269	7,930	11,507
General and administrative	3,471	2,247	5,618	4,850
Total operating expenses	6,769	8,516	13,548	16,357
Loss from operations	(6,492)	(8,402)	(13,042)	(15,999)
Other income (expense):
Other income, net	1	1,826	139	3,134
Loss on extinguishment of debt	0	0	(915)	0
Interest expense	0	(330)	(247)	(565)
Total other income (expense), net	1	1,496	(1,023)	2,569
Net loss and comprehensive loss	$ (6,491)	$ (6,906)	$ (14,065)	$ (13,430)
Net loss per share applicable to common stockholders—basic and diluted (in dollars per share)	$ (0.33)	$ (0.36)	$ (0.71)	$ (0.72)
Weighted-average number of common shares used in net loss per share applicable to common stockholders—basic and diluted (in shares)	19,874	19,087	19,756	18,532