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Assumptions Used in Estimating Fair Value of Stock Options Granted (Detail) (USD $)
3 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term 3 years 7 months 6 days 3 years 8 months 12 days
Volatility 98.37% 92.70%
Annual dividend per share $ 0.00 $ 0.00
Risk-free interest rate 1.65% 0.80%