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Share Based Compensation (Stock Based Compensation Awards, Expected Fair Value Assumptions) (Detail)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility, minimum 0.00% 73.50% 74.40%
Expected volatility, maximum 0.00% 75.40% 75.90%
Expected term (in years) 0 years 4 years 4 years
Risk-free rate, minimum 0.00% 0.90% 1.18%
Risk-free rate, maximum 0.00% 2.11% 2.58%
Annual forfeiture rate 0.00% 10.00% 10.00%