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Other Items - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2014
Mar. 31, 2015
Dec. 31, 2014
Asset Retirement Obligation [Line Items]      
Development project charges $ 1,440us-gaap_NoncashProjectAbandonmentCosts    
Deferred project costs   0us-gaap_OtherDeferredCostsGross 0us-gaap_OtherDeferredCostsGross
Gain on settlement of acquisition related contingent consideration (1,058)us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1    
Industrial Service Management Business [Member]      
Asset Retirement Obligation [Line Items]      
Gain on settlement of acquisition related contingent consideration 1,058us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1
/ us-gaap_BusinessAcquisitionAxis
= cwst_IndustrialServiceManagementBusinessMember
   
Maine Energy Facility [Member]      
Asset Retirement Obligation [Line Items]      
Development project charges $ 1,440us-gaap_NoncashProjectAbandonmentCosts
/ us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis
= cwst_MaineEnergyFacilityMember