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Fair Value of Each Option Award on the Grant Date Using the Black-Scholes Option-Pricing Model (Detail)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]      
Dividend yield 0.00% 0.00% 0.00%
Risk-free interest rate 0.87% 1.63% 1.88%
Expected volatility 35.70% 39.50% 31.40%
Expected term (years) 6 years 3 months 18 days 6 years 3 months 18 days 6 years 3 months 18 days