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Stock-Based Compensation - Summary of Assumptions Used in Options (Detail)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Stock Based Compensation [Line Items]      
Expected dividend yield     0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
Weighted average volatility 23.99%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate 25.89%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate 28.56%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate
Minimum      
Stock Based Compensation [Line Items]      
Expected life (years) 3 years 3 years 6 months 3 years 6 months
Risk-free interest rate 0.87%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		 0.40%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		 0.38%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Expected dividend yield 1.77%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Expected volatility 23.50%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		 25.40%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		 28.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Maximum      
Stock Based Compensation [Line Items]      
Expected life (years) 5 years 3 months 6 years 6 years
Risk-free interest rate 1.66%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 1.99%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 0.083%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Expected dividend yield 2.39%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 2.19%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Expected volatility 25.32%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 27.60%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 30.30%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember