Condensed Consolidated Statements of Comprehensive Loss (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Condensed Consolidated Statements of Comprehensive Loss
Contract revenue		$ 15		$ 31
Operating expenses:
Research and development	6,721	9,646	14,411	15,966
General and administrative	2,813	1,940	5,283	3,959
Total operating expenses	9,534	11,586	19,694	19,925
Loss from operations	(9,534)	(11,571)	(19,694)	(19,894)
Other income (expense):
Interest income, net	(290)	(236)	(550)	(488)
Other income (expense), net	10	(2)	22	(1)
Net loss	(9,814)	(11,809)	(20,222)	(20,383)
Other comprehensive income (loss):
Net unrealized gains (losses) on marketable securities	2	17	(2)	17
Comprehensive loss	$ (9,812)	$ (11,792)	$ (20,224)	$ (20,366)
Basic and diluted net loss per common share (in dollars per share)	$ (0.30)	$ (0.49)	$ (0.61)	$ (1.02)
Weighted average common shares outstanding used to calculate basic and diluted net loss per common share (in shares)	32,981,396	24,189,819	32,973,892	19,922,307