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Income Taxes - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Income Taxes [Line Items]        
Percentage of income attributable to wholly-owned operations and investments for which income tax expense and effective tax rate calculated 100.00%wso_PercentOfOperationAndInvestmentIncomeForWhichIncomeTaxExpenseAndEffectiveTaxRateCalculated      
Undistributed earnings of foreign subsidiaries $ 80,000us-gaap_UndistributedEarningsOfForeignSubsidiaries      
Valuation allowance   75us-gaap_DeferredTaxAssetsValuationAllowanceNoncurrent    
State and other net operating loss carry forwards 7,231us-gaap_OperatingLossCarryforwards      
Gross unrecognized tax benefits 3,719us-gaap_UnrecognizedTaxBenefits 3,135us-gaap_UnrecognizedTaxBenefits 2,474us-gaap_UnrecognizedTaxBenefits 2,424us-gaap_UnrecognizedTaxBenefits
Unrecognized tax benefits that, if recognized, would affect the effective tax rate 2,417us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate 2,038us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate    
Estimated accrued interest and penalties resulting from unrecognized tax benefits $ 729us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued $ 630us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued    
Minimum        
Income Taxes [Line Items]        
State and other net operating loss carry forwards expiration date 2015      
Maximum        
Income Taxes [Line Items]        
State and other net operating loss carry forwards expiration date 2034