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Warrant Liability - Assumptions Used for Black-Scholes Option Pricing Model1 (Detail) (USD $)
3 Months Ended 9 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Dec. 31, 2012
Sep. 30, 2013
Warrant Agreement 2009 [Member]
Dec. 31, 2012
Warrant Agreement 2009 [Member]
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)