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Assumptions Used to Estimate Fair Value of Stock Options Granted, SARs Granted and Employee Share Purchase Plan Granted to Employees (Detail)
3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected dividend yield 0.00% 0.00% 0.00% 0.00%
Stock options and SARs, Expected volatility, Minimum 39.00% 47.00% 38.00% 47.00%
Stock options and SARs, Expected volatility, Maximum 53.00% 55.00% 54.00% 58.00%
Risk-free interest rate, Minimum 0.10% 0.20% 0.10% 0.10%
Risk-free interest rate, Maximum 2.00% 1.00% 2.50% 1.20%
Expected forfeiture 10.00% 10.00% 10.00% 10.00%
Expected forfeiture (executives)   5.00% 5.00% 5.00%
Contractual term of up to 7 years 7 years 10 years 10 years
Common Stock
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected dividend yield 0.00% 0.00% 0.00% 0.00%
Stock options and SARs, Expected volatility, Minimum 34.00% 47.00% 34.00% 41.00%
Stock options and SARs, Expected volatility, Maximum 52.00% 55.00% 53.00% 61.00%
Risk-free interest rate, Minimum 0.10% 0.20% 0.10% 0.10%
Risk-free interest rate, Maximum 0.20% 1.00% 0.20% 0.60%
Expected forfeiture 0.00% 0.00% 0.00% 0.00%
Contractual term of up to 24 months 24 months 24 months 24 months
Employees
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Suboptimal exercise multiple 2.1 2.1 2.1 2.1
Executives
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Suboptimal exercise multiple   2.4 2.4 2.4