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Estimated Fair Value of Each Option Award at Grant Date by Using Black-Scholes Option Pricing Model (Detail) (Stock Option)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Share-Based Compensation [Line Items]    
Dividend yield 0.00% 0.00%
Expected volatility, in years 125.00%  
Expected volatility, in years minimum   82.00%
Expected volatility, in years maximum   136.00%
Risk-free interest rates minimum 0.80% 0.40%
Risk-free interest rates maximum 0.90% 2.60%
Expected lives, in years 5 years  
Minimum
   
Share-Based Compensation [Line Items]    
Expected lives, in years   2 years
Maximum
   
Share-Based Compensation [Line Items]    
Expected lives, in years   7 years