Annual report pursuant to section 13 and 15(d)

Valuation Assumptions Used in Computation of Stock Option Expense (Detail)

v2.4.0.8
Valuation Assumptions Used in Computation of Stock Option Expense (Detail)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected volatility, minimum 75.80% 0.00%
Expected volatility, maximum 118.60% 84.70%
Weighted-average volatility 78.10% 81.00%
Risk-free interest rate, minimum 0.30% 0.40%
Risk-free interest rate, maximum 0.90% 2.20%
Expected dividend yield 0.00% 0.00%
Minimum
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life in years 3 years 6 months 3 years 6 months
Maximum
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life in years 8 years 7 months 6 days 8 years 7 months 6 days