Condensed Consolidated Statements of Operations (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues:
Grant revenues	$ 0	$ 0	$ 0	$ 147
Total revenues				147
Operating expenses:
Research and development	17,623	11,743	51,879	35,061
General and administrative	4,171	2,796	12,236	8,324
Total operating expenses	21,794	14,539	64,115	43,385
Loss from operations	(21,794)	(14,539)	(64,115)	(43,238)
Interest expense, net	(721)	(457)	(1,915)	(1,429)
Net loss	$ (22,515)	$ (14,996)	$ (66,030)	$ (44,667)
Net loss per common share:
Basic and diluted net loss per common share (in dollars per share)	$ (0.33)	$ (0.25)	$ (0.96)	$ (0.77)
Basic and diluted weighted average number of common shares outstanding (in shares)	69,047,161	60,661,720	69,024,656	58,235,263