Annual report pursuant to Section 13 and 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 $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share based Compensation Arrangement Assumptions Used to Estimate Fair Values of Share Options Granted [Line Items]      
Expected term (years) 3 years 8 months 12 days 4 years 1 month 24 days 4 years 6 months 15 days
Volatility 97.00% 105.00% 91.00%
Annual dividend per share $ 0.00 $ 0.00 $ 0.00
Risk-free interest rate 0.77% 1.53% 1.94%