Quarterly Consolidated Financial Data (Unaudited) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended								12 Months Ended							36 Months Ended	86 Months Ended
	Nov. 30, 2011	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	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007	Dec. 31, 2006	Dec. 31, 2012	Dec. 31, 2012
Costs and expenses:
Research and Development		$ 9,085	$ 7,245	$ 7,626	$ 5,338	$ 5,703	$ 3,883	$ 2,355	$ 1,478	$ 29,294	$ 13,419	$ 9,559						$ 57,707
Purchased in-process research and development			1,000							1,000								29,157
General and administrative		2,447	1,843	1,919	1,732	2,222	1,103	1,524	1,897	7,941	6,745	6,562						27,585
Loss from Operations		(11,532)	(10,088)	(9,545)	(7,070)	(7,925)	(4,986)	(3,879)	(3,375)	(38,235)	(20,164)	(16,121)						(114,449)
Other income		250		256		362				506	362	494					1,362	1,363
Interest and investment income		68	63	48	39	26	20	20	24	218	90	109						496
Interest expense									(12)		(12)							(12)
Change in fair value of derivative instruments-warrants		(764)	140	(1,317)	8	1,911	4,383	(698)	(339)	(1,933)	5,257	297						3,621
Total Other Income/(Loss)		(446)	203	(1,013)	47	2,299	4,403	(678)	(327)	(1,209)	5,697	900						5,468
Net loss		$ (11,978)	$ (9,885)	$ (10,558)	$ (7,023)	$ (5,626)	$ (583)	$ (4,557)	$ (3,702)	$ (39,444)	$ (14,467)	$ (15,221)	$ (8,124)	$ (31,757)	$ (20)	$ (20)		$ (109,053)
Weighted average common shares outstanding-basic and diluted		66,194,306	65,806,178	60,416,068	54,298,079	48,657,013	47,308,946	46,642,901	46,167,416	61,702,277	47,598,240	44,875,356
Earnings per common share-basic and diluted:
Net per common share-basic and diluted (in dollars per share)		$ (0.18)	$ (0.15)	$ (0.17)	$ (0.13)	$ (0.12)	$ (0.01)	$ (0.10)	$ (0.08)	$ (0.64)	$ (0.30)	$ (0.34)
Reverse stock split ratio	0.5