Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation - Stock-Based Compensation Expense Recognized (Detail)

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Stock-Based Compensation - Stock-Based Compensation Expense Recognized (Detail) (USD $)
3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Total Stock based compensation $ 1,538,343 $ 799,391 $ 1,624,165 $ 1,057,218
Research and Development Expense [Member]
       
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Total Stock based compensation 183,168 105,858 158,575 116,726
Selling, General and Administrative Expenses [Member]
       
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Total Stock based compensation $ 1,355,175 $ 693,533 $ 1,465,590 $ 940,492