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Weighted-Average Assumptions Used in Black-Scholes Option Pricing Model Which Was Used to Estimate Grant Date Fair Value per Share (Detail) (Employee Stock Option [Member], USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Employee Stock Option [Member]
   
Schedule of Weighted Average Assumptions for Fair Values of Stock Options[Line Items]    
Shares underlying options granted 1,011 825
Weighted-average grant date fair value $ 27.75 $ 27.89
Weighted-average volatility 59.00% 63.00%
Weighted-average expected term (years) 4 years 4 months 24 days 5 years 2 months 12 days
Range of risk-free rates, minimum 0.60% 1.00%
Range of risk-free rates, maximum 0.70% 1.00%
Expected dividend yield 0.00% 0.00%