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Assumptions Used to Estimate Fair Value on Grant Date, Stock Options (Detail) (Stock Options)
6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Stock Options
   
Schedule of Weighted Average Assumptions for Fair Values of Stock Options[Line Items]    
Risk-free interest rate 1.30% 2.60%
Expected volatility 39.20% 27.40%
Weighted average expected life in years 6 years 292 days 7 years 146 days
Dividend yield 3.60% 3.70%