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
STATEMENTS OF OPERATIONS [Abstract]
Government contracts	$ 4,268	$ 5,583	$ 10,985	$ 17,328
Research and development collaborations	534	182	1,182	182
Total revenue	4,802	5,765	12,167	17,510
Costs and expenses:
Cost of government contracts revenue	2,276	3,838	5,619	12,740
Research and development	13,948	6,642	33,989	17,270
General and administrative	3,857	2,134	10,740	7,670
Total costs and expenses	20,081	12,614	50,348	37,680
Loss from operations	(15,279)	(6,849)	(38,181)	(20,170)
Other income (expense):
Interest income	53	39	149	111
Interest expense	(64)	(6)	(132)	(12)
Other expense	(10)		(10)
Change in fair value of warrant liability		(401)	267	(401)
Loss from operations before income tax	(15,300)	(7,217)	(37,907)	(20,472)
Income tax expense			22
Net loss	$ (15,300)	$ (7,217)	$ (37,929)	$ (20,472)
Basic and diluted net loss per share	$ (0.09)	$ (0.05)	$ (0.24)	$ (0.16)
Basic and diluted weighted average number of common shares outstanding	168,537	134,178	156,555	127,246