STATEMENTS OF OPERATIONS (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
STATEMENTS OF OPERATIONS [Abstract]
Government contracts	$ 3,441	$ 4,642
Research and development collaborations	392
Total revenue	3,833	4,642
Costs and expenses:
Cost of government contracts revenue	1,712	3,786
Research and development	9,432	5,338
General and administrative	2,694	2,985
Total costs and expenses	13,838	12,109
Loss from operations	(10,005)	(7,467)
Other income (expense):
Interest income	48	33
Interest expense	(22)	(3)
Change in fair value of warrant liability		101
Loss from operations before income tax	(9,979)	(7,336)
Income tax expense	17
Net loss	$ (9,996)	$ (7,336)
Basic and diluted net loss per share	$ (0.07)	$ (0.06)
Basic and diluted weighted average number of common shares outstanding	148,448	120,558