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Stock-Based Compensation - Fair Value of Date of Grant Using Black-Scholes Option-Pricing Model (Detail) - Stock Options [Member]
6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]    
Dividend yield 2.00% 1.80%
Risk-free interest rate 0.70% 0.50%
Expected volatility 33.00% 39.00%
Expected life (in years) 5 years 2 months 12 days 5 years 2 months 12 days