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Contributions in Multiemployer Pension Plans (Parenthetical) (Detail) (USD $)
 12 Months Ended
Dec. 31, 2014
Defined Contribution Plan Disclosure [Line Items]  
Percentage of contribution to the plan 5.00%wab_DefinedContributionPlanPercentageOfContribution
Increasing in weekly pension fund contribution rates $ 75wab_DefinedContributionPlansIncreaseDecreaseInContributionRate
Surcharge Imposed 5.00%wab_MultiemployerPlansSurchargeImposed
Defined Contribution Plan  
Defined Contribution Plan Disclosure [Line Items]  
Surcharge Imposed 10.00%wab_MultiemployerPlansSurchargeImposed
/ us-gaap_DefinedContributionPlanTypeAxis
= wab_DefinedContributionPlanMember
Red Zone  
Defined Contribution Plan Disclosure [Line Items]  
Percentage of funds required in the critical status 65.00%wab_PercentageOfFundsRequiredInCriticalStatus
/ us-gaap_DefinedContributionPlanTypeAxis
= wab_RedZoneMember
Yellow Zone  
Defined Contribution Plan Disclosure [Line Items]  
Percentage of funds required in the critical status 80.00%wab_PercentageOfFundsRequiredInCriticalStatus
/ us-gaap_DefinedContributionPlanTypeAxis
= wab_YellowZoneMember
Green Zone  
Defined Contribution Plan Disclosure [Line Items]  
Percentage of funds required in the critical status 80.00%wab_PercentageOfFundsRequiredInCriticalStatus
/ us-gaap_DefinedContributionPlanTypeAxis
= wab_GreenZoneMember