Condensed Consolidated Statements of Operations and Comprehensive Loss (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		77 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013
Revenues:
Collaboration revenue	$ 209	$ 208	$ 626	$ 1,075	$ 2,927
Grant revenue		320	345	952	2,084
Total revenue	209	528	971	2,027	5,011
Operating expenses:
Research and development	3,378	3,315	8,976	8,596	53,955
General and administrative	1,979	863	4,768	2,944	28,839
Total operating expenses	5,357	4,178	13,744	11,540	82,794
Loss from operations	(5,148)	(3,650)	(12,773)	(9,513)	(77,783)
Other income (expense), net	(925)	(463)	(2,382)	(571)	(2,987)
Net loss and comprehensive loss	$ (6,073)	$ (4,113)	$ (15,155)	$ (10,084)	$ (80,770)
Net loss per common share, basic and diluted (in dollars per share)	$ (4.81)	$ (3.51)	$ (12.24)	$ (9.52)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	1,262,546	1,171,012	1,238,567	1,059,113