Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended		398 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013
Income Statement [Abstract]
Revenues from license fees, grants and research contracts	$ 4,168	$ 7,574	$ 11,593	$ 29,993	$ 185,141
Operating expenses:
Research and development	21,087	10,914	47,833	39,568	433,501
General and administrative	8,014	3,565	21,195	9,761	140,282
Acquired in-process research and development					29,461
Operating loss	(24,933)	(6,905)	(57,435)	(19,336)	(418,103)
Other (loss) income:
Interest income and other, net	63	67	281	270	9,804
Loss on change in warrant valuation	(17,160)	(42,716)	(46,011)	(40,154)	(112,979)
Realized gain on sale of short-term securities - available-for-sale					3,863
Write-down of short-term securities - available-for-sale					(17,001)
Total other loss	(17,097)	(42,649)	(45,730)	(39,884)	(116,313)
Net loss	(42,030)	(49,554)	(103,165)	(59,220)	(534,416)
Other comprehensive (loss) income:
Write-down of short-term securities - available-for-sale					17,001
Realized gain on sale of short-term securities - available-for-sale					(3,863)
Unrealized loss on short-term securities - available-for-sale					(13,138)
Total other comprehensive (loss) income
Comprehensive loss	$ (42,030)	$ (49,554)	$ (103,165)	$ (59,220)	$ (534,416)
Net loss per share - basic	$ (1.24)	$ (2.17)	$ (3.17)	$ (2.61)
Net loss per share - diluted	$ (1.24)	$ (2.17)	$ (3.17)	$ (2.61)
Weighted average number of common shares outstanding for computing basic net loss per share	33,943	22,824	32,588	22,691
Weighted average number of common shares outstanding for computing diluted net loss per share	33,943	22,824	32,588	22,691