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Commitments and Contingencies - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 1 Months Ended
Mar. 31, 2015
Sep. 30, 2011
Nov. 30, 2011
Apr. 30, 2011
May 31, 2009
Greenwood Street Landfill [Member]          
Contingencies And Commitments [Line Items]          
Future remediation costs $ 129us-gaap_LitigationSettlementAmount
/ us-gaap_LitigationCaseAxis
= cwst_GreenwoodStreetLandfillMember
       
Greenwood Street Landfill [Member] | Administrative Penalty [Member]          
Contingencies And Commitments [Line Items]          
Future remediation costs 172us-gaap_LitigationSettlementAmount
/ us-gaap_LitigationCaseAxis
= cwst_GreenwoodStreetLandfillMember
/ us-gaap_OtherCommitmentsAxis
= cwst_AdministrativePenaltyMember
       
Potsdam Environmental Remediation Liability [Member]          
Contingencies And Commitments [Line Items]          
Scrap yard and solid waste transfer station 25cwst_ScrapYardAndSolidWasteTransferStation
/ us-gaap_EnvironmentalRemediationSiteAxis
= cwst_PotsdamEnvironmentalLiabilityMember
       
Estimate of total undiscounted costs associated with implementing the preferred remedies       12,130cwst_UndiscountedCostsPreferredRemedies
/ us-gaap_EnvironmentalRemediationSiteAxis
= cwst_PotsdamEnvironmentalLiabilityMember
10,219cwst_UndiscountedCostsPreferredRemedies
/ us-gaap_EnvironmentalRemediationSiteAxis
= cwst_PotsdamEnvironmentalLiabilityMember
Risk free interest rate 1.70%us-gaap_AccrualForEnvironmentalLossContingenciesDiscountRate
/ us-gaap_EnvironmentalRemediationSiteAxis
= cwst_PotsdamEnvironmentalLiabilityMember
       
Potsdam Environmental Remediation Liability [Member] | Motors Liquidation Trust - DEC [Member]          
Contingencies And Commitments [Line Items]          
Future remediation costs   3,000us-gaap_LitigationSettlementAmount
/ us-gaap_EnvironmentalRemediationSiteAxis
= cwst_PotsdamEnvironmentalLiabilityMember
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= cwst_MotorsLiquidationTrustDecMember
     
Potsdam Environmental Remediation Liability [Member] | Motors Liquidation Trust - Casella Waste Systems, Inc [Member]          
Contingencies And Commitments [Line Items]          
Future remediation costs     $ 100us-gaap_LitigationSettlementAmount
/ us-gaap_EnvironmentalRemediationSiteAxis
= cwst_PotsdamEnvironmentalLiabilityMember
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= cwst_MotorsLiquidationTrustMember