Quarterly report pursuant to Section 13 or 15(d)

Assumptions Used in Estimating Fair Value of Stock Options Granted (Detail)

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Assumptions Used in Estimating Fair Value of Stock Options Granted (Detail) (USD $)
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Share based Compensation Arrangement Assumptions Used to Estimate Fair Values of Share Options Granted [Line Items]    
Expected term 3 years 8 months 12 days 4 years 1 month 6 days
Volatility 92.70% 102.00%
Annual dividend per share $ 0.00 $ 0.00
Risk-free interest rate 0.80% 0.93%