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Stock-Based Compensation - Assumptions Used to Determine the Fair Value of the Awards with Market-Based (Detail) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested [Roll Forward]        
Expected dividends per share $ 0.90 $ 0.80 $ 0.90 $ 0.80
Expected volatility, minimum 41.50% 36.70% 41.50% 36.70%
Expected volatility, maximum 51.60% 50.00% 51.60% 50.00%
Risk-free interest rate, minimum 0.00% 0.10% 0.00% 0.10%
Risk-free interest rate, maximum 2.00% 1.20% 2.00% 1.20%
Estimated cost of capital 9.30%   9.30%  
Estimated cost of capital, minimum   11.90%   11.90%
Estimated cost of capital, maximum   12.10%   12.10%
Expected life (in years) 6 years 6 years 6 years 6 years