Accrued Expenses (Detail) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Schedule of Accrued Liabilities [Line Items]
Payroll and benefits	$ 2,172,045	$ 2,498,492
Professional fees	452,140	1,052,058
Research grants	1,179,007	1,313,280
Other	585,810	457,764
Total	$ 4,389,002	$ 5,321,594