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Black-Scholes-Merton Option Pricing Model for Employee and Director Stock Options Granted (Detail) (USD $)
9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]    
Expected dividend yield 0.00% 0.00%
Weighted average expected volatility 64.00% 63.00%
Weighted average expected term (years) 5 years 10 months 2 days 6 years 11 days
Weighted average risk-free rate 1.76% 1.28%
Weighted average fair value per share $ 7.14 $ 3.98