Warrant Liability - Assumptions Used for Black-Scholes Option Pricing Model1 (Detail) (USD $)
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3 Months Ended | 9 Months Ended | 9 Months Ended | 12 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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Dec. 31, 2012
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Sep. 30, 2013
Warrant Agreement 2009 [Member]
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Dec. 31, 2012
Warrant Agreement 2009 [Member]
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Class of Warrant or Right [Line Items] | |||||||
Expected life (years) | 1 year 7 months 6 days | 2 years 3 months 18 days | |||||
Risk-free interest rate | 0.30% | 0.30% | |||||
Expected volatility | 86.10% | 94.50% | |||||
Expected dividend yield | 0.00% | 0.00% | |||||
Fair value of warrant liability | $ 8,420,954 | $ 8,420,954 | $ 9,265,365 | $ 15,260 | $ 63,340 | ||
Change in fair value of warrant liability | $ 143,511 | $ 11,239,465 | $ (425,570) | $ 9,974,685 | $ (48,080) |