Subsequent Events (Details 2) (USD $)					0 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011	Oct. 04, 2013 Subsequent event	Sep. 30, 2013 Pro Forma
Actual balance sheet data and pro forma balance sheet data
Cash and cash equivalents	$ 19,082,000	$ 9,087,000	$ 5,464,000	$ 6,387,000		$ 59,127,000
Accounts payable and accrued expenses	3,725,000	2,268,000				2,344,000
Long-term accrued expenses	137,000	110,000				79,000
Common stock	1,000	1,000				20,000
Additional paid-in capital	14,367,000	12,789,000				136,398,000
Deficit accumulated during the development stage	(80,770,000)	(65,615,000)				(81,024,000)
Total stockholders' (deficit) equity	(66,402,000)	(52,825,000)				55,394,000
Aggregate non-cash charge related to the final fair value adjustment of the exchangeable share liability and the preferred stock warrant liability					$ 500,000