Condensed Consolidated Statements of Operations and Comprehensive Loss (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		404 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014
Income Statement [Abstract]
Revenue from license fees, grants and research contracts	$ 6,088	$ 4,474	$ 193,855
Operating expenses:
Research and development	20,906	13,762	479,483
General and administrative	10,303	6,127	160,984
Acquired in-process research and development			29,461
Operating loss	(25,121)	(15,415)	(476,073)
Other income (loss):
Interest income and other, net	99	237	9,948
Loss on change in warrant valuation	(3,251)	(26,906)	(92,246)
Realized gain on sale of available-for-sale securities			3,863
Write-down of available-for-sale securities			(17,001)
Total other loss	(3,152)	(26,669)	(95,436)
Net loss	(28,273)	(42,084)	(571,509)
Other comprehensive income (loss):
Write-down of available-for-sale securities			17,001
Realized gain on sale of available-for-sale securities			(3,863)
Unrealized loss on available-for-sale securities	(59)		(13,197)
Total other comprehensive loss	(59)		(59)
Comprehensive loss	$ (28,332)	$ (42,084)	$ (571,568)
Net loss per share:
Net loss per share - basic and diluted	$ (0.75)	$ (1.32)
Weighted average number of common shares outstanding for computing basic and diluted net loss per share	37,821	31,813