Subsequent Event (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	88 Months Ended									0 Months Ended
	Mar. 31, 2013	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007	Dec. 31, 2005	Mar. 31, 2013 Pro-forma	Apr. 16, 2013 Subsequent Event	Apr. 16, 2013 Subsequent Event Public Offering
Subsequent Event
Number of shares of common stock issued											16,375,000
Common stock price (in dollars per share)											$ 5.50
Net proceeds	$ 4,671	$ 121,105									$ 84,400
Term of options granted to underwriters											30 days
Options granted to underwriters (in shares)											2,456,250
Cash, cash equivalents and available for sale securities	21,116	21,116								105,560		84,444
Total Assets	22,890	22,890	37,405							107,334		84,444
Common Stock	8	8	7							10		2
Additional paid-in capital	134,991	134,991	133,878							219,433		84,442
Deficit accumulated during development stage	(127,750)	(127,750)	(109,053)							(127,750)
Total Stockholders' Equity	7,249	7,249	24,832	9,798	(4,099)	7,484	(1,156)	(11)	20	91,693		84,444
Total Liabilities and Stockholders' Equity	$ 22,890	$ 22,890	$ 37,405							$ 107,334		$ 84,444
Common Shares Outstanding	73,779,680	73,779,680	66,621,832							90,154,680		16,375,000