Organization, Operations and Liquidity - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Product Information [Line Items]
Number of subjects in open label safety study	500
Proceeds from Issuance of Private Placement	$ 23,000,000
Deficit accumulated during development stage	201,858,000	191,735,000
Cash and cash equivalents	29,583,000	4,565,000	7,070,000	2,957,000
Accounts payable and accrued expenses	1,800,000
Private Placement [Member]
Product Information [Line Items]
Issuance of common stock, share	2,145,636
Common stock, price per share	$ 11.00
One year [Member]
Product Information [Line Items]
Number of subjects required for registration	100
Six months [Member]
Product Information [Line Items]
Number of subjects required for registration	800
Issuance During Period 2nd [Member]
Product Information [Line Items]
Issuance of common stock, share	2,463,537
Common stock, price per share	$ 4.50
Issuance of stock net of offering costs	$ 10,300,000