Accounting for Stock-Based Compensation - Employee and Non-Employee Share Based Compensation Expense Allocation (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Total stock-based compensation expense	$ 818,300	$ 922,554	$ 2,245,565	$ 2,499,091
Research and Development Expenses [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Total stock-based compensation expense	195,670	345,390	496,418	841,909
General and Administrative Expenses [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Total stock-based compensation expense	$ 622,630	$ 577,164	$ 1,749,147	$ 1,657,182