Organization and Business (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	1 Months Ended		12 Months Ended
	Jan. 31, 2013	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Organization and Business [Abstract]
MedImmune upfront payment receivable	$ 5,000,000
CytoDyn upfront payment		3,500,000	3,500,000
Common stock, issued (in shares)		12,650
Common stock public offering price (in dollars per share)		$ 2.00
Common stock public offering proceeds		23,300,000	23,348,000	0	0
Funding and Financial Matters [Abstract]
Cash and cash equivalents at end of period		58,838,000	58,838,000	70,105,000	47,918,000	90,903,000
Decrease in cash and cash equivalents			11,267,000	(22,187,000)	42,985,000
Minimum number of years cash will fund operations			1 year
Cash, cash equivalents and auction rate securities		62,078,000	62,078,000	73,437,000
Decrease in cash, cash equivalents and auction rate securities			11,359,000
Authorized amount of common shares under stock repurchase program, maximum			15,000,000
Remaining authorized amount of common shares under stock repurchase program			12,300,000
Stock repurchased during the period, value			$ 0	$ 0	$ 0