NATURE OF BUSINESS AND OVERVIEW (Details) (USD $)	1 Months Ended	2 Months Ended	3 Months Ended								12 Months Ended			1 Months Ended
	May 30, 2011	Mar. 31, 2012	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	Feb. 28, 2013 Subsequent event	Jan. 31, 2013 Subsequent event
NATURE OF BUSINESS AND OVERVIEW
Cash, cash equivalents and marketable securities			$ 84,000,000								$ 84,000,000
Working capital			67,400,000								67,400,000
Term Loan			11,300,000								11,300,000
Net Loss			(16,807,000)	(15,027,000)	(13,773,000)	(13,516,000)	(12,732,000)	(11,772,000)	(10,236,000)	(10,059,000)	(59,123,000)	(44,799,000)	(2,533,000)
Net cash used in operations											(49,782,000)	(35,658,000)	(30,372,000)
Shares of common stock sold under the Cantor Agreement														13,800,000	2,433,608
Net proceeds from sale of common stock											83,784,000	36,023,000	1,014,000	97,000,000	17,100,000
Common stock in an underwritten public offering issued (in shares)	11,500,000	12,075,000												13,800,000
Amount raised from shares issued in underwritten public offering	$ 33,700,000	$ 43,400,000									$ 43,483,000	$ 33,695,000		$ 97,000,000