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Stock-Based Compensation - Stock-Based Compensation Expense Recognized (Detail) (USD $)
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3 Months Ended | 9 Months Ended | ||
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Sep. 30, 2013
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Sep. 30, 2012
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Sep. 30, 2013
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Sep. 30, 2012
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| 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 |
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Research and Development Expense [Member]
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| Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||||
| Total Stock based compensation | 183,168 | 105,858 | 158,575 | 116,726 |
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Selling, General and Administrative Expenses [Member]
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| 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 |