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Assumptions Used to Estimate Fair Value (Detail) - Stock Options
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 2.20% 1.50% 0.80%
Expected volatility 43.00% 46.00% 57.00%
Risk free interest rate 1.30% 1.50% 1.90%
Weighted average expected option life in years 5 years 9 months 18 days 5 years 8 months 12 days 5 years 9 months 18 days