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Stock-Based Compensation - Assumptions Used for Computing Stock-Based Employee Compensation Expense (Detail)
9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]    
Risk-free interest rate 2.70% 1.74%
Dividend yield 2.00% 2.00%
Stock price volatility 18.35% 32.88%
Expected term 10 years 10 years