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Divestiture Transactions - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 0 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Mar. 31, 2015 | Feb. 09, 2015 | Apr. 30, 2013 | Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Gain on divestiture | $ 4,935 cwst_DivestitureTransactions |  |  |
Other accrued liabilities | 16,200 us-gaap_OtherAccruedLiabilitiesCurrent |  |  | 16,667 us-gaap_OtherAccruedLiabilitiesCurrent
Proceeds from sale of assets | 4,550 us-gaap_ProceedsFromSalesOfBusinessAffiliateAndProductiveAssets |  |  |
Casella-Altela Regional Environmental Services, LLC [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Gain on divestiture |  | 2,850 cwst_DivestitureTransactions / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = cwst_CasellaAltelaRegionalEnvironmentalServicesLlcMember |  |
Membership interest | 51.00%us-gaap_MinorityInterestOwnershipPercentageByParent / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = cwst_CasellaAltelaRegionalEnvironmentalServicesLlcMember |  |  |
Proceeds from sale of assets |  | 3,500 us-gaap_ProceedsFromSalesOfBusinessAffiliateAndProductiveAssets / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = cwst_CasellaAltelaRegionalEnvironmentalServicesLlcMember |  |
Casella-Altela Regional Environmental Services, LLC [Member] | Other Assets [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Gain on divestiture | 928 cwst_DivestitureTransactions / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherAssetsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = cwst_CasellaAltelaRegionalEnvironmentalServicesLlcMember |  |  |
Proceeds from sale of assets |  | 1,050 us-gaap_ProceedsFromSalesOfBusinessAffiliateAndProductiveAssets / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherAssetsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = cwst_CasellaAltelaRegionalEnvironmentalServicesLlcMember |  |
Casella-Altela Regional Environmental Services, LLC [Member] | Altela, Inc. [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Membership interest |  | 49.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / dei_LegalEntityAxis = cwst_AltelaIncMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = cwst_CasellaAltelaRegionalEnvironmentalServicesLlcMember |  |
Maine Energy Facility [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Undiscounted purchase consideration |  |  | 6,650 us-gaap_SignificantAcquisitionsAndDisposalsAcquisitionCostsOrSaleProceeds / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = cwst_MaineEnergyFacilityMember |
Undiscounted purchase consideration paid in installments |  |  | 21 years |
Gain on divestiture | 1,157 cwst_DivestitureTransactions / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = cwst_MaineEnergyFacilityMember |  |  |
Other accrued liabilities | $ 115 us-gaap_OtherAccruedLiabilitiesCurrent / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = cwst_MaineEnergyFacilityMember |  |  |

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