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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 | $ 129 us-gaap_LitigationSettlementAmount / us-gaap_LitigationCaseAxis = cwst_GreenwoodStreetLandfillMember |  |  |  |
Greenwood Street Landfill [Member] | Administrative Penalty [Member] |  |  |  |  |
Contingencies And Commitments [Line Items] |  |  |  |  |
Future remediation costs | 172 us-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 | 25 cwst_ScrapYardAndSolidWasteTransferStation / us-gaap_EnvironmentalRemediationSiteAxis = cwst_PotsdamEnvironmentalLiabilityMember |  |  |  |
Estimate of total undiscounted costs associated with implementing the preferred remedies |  |  |  | 12,130 cwst_UndiscountedCostsPreferredRemedies / us-gaap_EnvironmentalRemediationSiteAxis = cwst_PotsdamEnvironmentalLiabilityMember | 10,219 cwst_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 |  | 3,000 us-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 |  |  | $ 100 us-gaap_LitigationSettlementAmount / us-gaap_EnvironmentalRemediationSiteAxis = cwst_PotsdamEnvironmentalLiabilityMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = cwst_MotorsLiquidationTrustMember |  |

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- Definition Acreage of scrap yard owned by WSI. + References No definition available. + Details
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- Definition Estimated undiscounted remediation costs. + References No definition available. + Details
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- Definition Rate applied to the undiscounted amount of environmental loss contingencies to arrive at the present value recorded as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q1) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section Y -Paragraph Question 1 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 + Details
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