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Schedule of Weighted Average Fair Values and Assumptions Used (Detail) (Employee Stock Option, USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Employee Stock Option
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average fair value $ 12.06 $ 9.72 $ 12.05
Assumptions:      
Expected volatility 41.00% 50.00%  
Dividend yield 0.00% 0.00%  
Risk-free interest rate 0.87% 0.84%  
Expected life 5 years 5 years