Unaudited Quarterly Results (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Revenues	$ 8,885	$ 1,117	$ 1,820	$ 2,226	$ 2,197	$ 5,804	$ 74,407	$ 2,388	$ 14,048	$ 84,796	$ 7,952
Net income (loss)	(324)	(11,301)	(10,720)	(13,086)	(10,746)	(11,432)	55,486	(22,927)	(35,431)	10,381	(69,725)
Net (loss) income per share - basic					$ (0.32)	$ (0.34)	$ 1.66	$ (0.69)	$ (1.02)	$ 0.31	$ (2.14)
Net (loss) income per share - diluted					$ (0.32)	$ (0.34)	$ 1.64	$ (0.69)	$ (1.02)	$ 0.31	$ (2.14)
Net income (loss) per share - basic and diluted (in dollars per share)	$ (0.01)	$ (0.33)	$ (0.32)	$ (0.39)					$ (1.02)		$ (2.14)
MedImmune [Member]
Segment Reporting Information [Line Items]
Revenues	5,000
CytoDyn [Member]
Segment Reporting Information [Line Items]
Revenues	2,800
Salix [Member]
Segment Reporting Information [Line Items]
Revenues							$ 59,500