CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Statement [Abstract]
Revenue	$ 229	$ 244
Operating expenses:
Research and development	4,632	5,238
General and administrative	2,147	2,603
Total operating expenses	6,779	7,841
Loss from operations	(6,550)	(7,597)
Other income (expense):
Other income, net	138	1,308
Loss on extinguishment of debt	(915)	0
Interest expense	(247)	(235)
Total other (expense) income, net	(1,024)	1,073
Net loss and comprehensive loss	$ (7,574)	$ (6,524)
Net loss per share applicable to common stockholders—basic and diluted (in dollars per share)	$ (0.39)	$ (0.36)
Weighted-average number of common shares used in net loss per share applicable to common stockholders—basic and diluted	19,639	17,971