Consolidated Statements of Operations and Comprehensive Loss (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended			401 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
Income Statement [Abstract]
Revenues from license fees, grants and research contracts	$ 14,219	$ 37,329	$ 46,990	$ 187,767
Operating expenses:
Research and development	72,909	52,402	66,862	458,577
General and administrative	31,594	14,630	16,055	150,681
Acquired in-process research and development				29,461
Operating loss	(90,284)	(29,703)	(35,927)	(450,952)
Other income (loss):
Interest income (expense) and other, net	326	354	587	9,849
Gain (loss) on change in warrant valuation	(22,027)	(91,938)	33,022	(88,995)
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 income (loss):	(21,701)	(91,584)	33,609	(92,284)
Net income (loss)	(111,985)	(121,287)	(2,318)	(543,236)
Other comprehensive income (loss):
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 income (loss)
Comprehensive loss	$ (111,985)	$ (121,287)	$ (2,318)	$ (543,236)
Loss per share:
Net loss per share-basic and diluted	$ (3.31)	$ (5.14)	$ (0.11)
Weighted average number of common shares outstanding for computing basic and diluted net loss per share (in thousands)	33,850	23,602	21,599