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 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Share Based Compensation Arrangement Assumptions Used To Estimate Fair Values Of Share Options Granted [Line Items]        
Expected term 3 years 7 months 6 days 3 years 8 months 12 days 3 years 7 months 24 days 3 years 9 months 18 days
Volatility 75.00% 103.00% 85.00% 103.00%
Annual dividend per share $ 0.00 $ 0.00 $ 0.00 $ 0.00
Risk-free interest rate 0.98% 0.87% 0.88% 0.88%