Organization (Details Textual) (USD $)	3 Months Ended
	Mar. 31, 2013 Candidate	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Organization (Textual) [Abstract]
Number of drug candidates	2
Cash and cash equivalents	$ 6,149,000	$ 10,096,000	$ 18,689,000	$ 24,571,000
Accumulated deficit	$ 398,465,000	$ 394,658,000
Quarter to which operations can be funded with current cash and cash equivalents and proceeds from follow-on public offering	Fourth quarter of 2014