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Long-Term Debt and Capital Leases - Additional Information (Detail) (USD $) | 12 Months Ended | 1 Months Ended | 8 Months Ended | 3 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Apr. 30, 2013 | Apr. 30, 2012 | Feb. 28, 2015 | Dec. 31, 2014 | Oct. 31, 2014 | Apr. 30, 2014 | Dec. 31, 2012
Debt Instrument [Line Items] |  |  |  |  |  |  |
Net proceeds from the offering sale | $ 42,184,000 us-gaap_ProceedsFromIssuanceOfCommonStock |  |  |  |  |  |
Aggregate principal amount | 496,205,000 us-gaap_DebtAndCapitalLeaseObligations |  |  | 535,711,000 us-gaap_DebtAndCapitalLeaseObligations |  | 508,019,000 us-gaap_DebtAndCapitalLeaseObligations |
Loss on debt extinguishment | 15,584,000 us-gaap_GainsLossesOnExtinguishmentOfDebt | 300,000 us-gaap_GainsLossesOnExtinguishmentOfDebt |  |  |  |  |
Write off Deferred Financing Costs [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Loss on debt extinguishment | 2,767,000 us-gaap_GainsLossesOnExtinguishmentOfDebt / us-gaap_ExtinguishmentOfDebtAxis = cwst_WriteOffDeferredFinancingCostsMember |  |  |  |  |  |
Write off Unamortized Original Issue Discount [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Loss on debt extinguishment | 2,074,000 us-gaap_GainsLossesOnExtinguishmentOfDebt / us-gaap_ExtinguishmentOfDebtAxis = cwst_WriteOffUnamortizedOriginalIssueDiscountMember |  |  |  |  |  |
Tender Premium and Tender Fees [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Loss on debt extinguishment | 10,743,000 us-gaap_GainsLossesOnExtinguishmentOfDebt / us-gaap_ExtinguishmentOfDebtAxis = cwst_TenderPremiumAndTenderFeesMember |  |  |  |  |  |
Class A Common Stock [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Net proceeds from the offering sale | 42,184,000 us-gaap_ProceedsFromIssuanceOfCommonStock / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember |  |  |  |  |  |
Abl Facility [Member] | Senior Subordinated Notes Due 2019 Notes [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Issuance of additional senior subordinated notes |  |  | 60,000,000 us-gaap_ProceedsFromIssuanceOfSubordinatedLongTermDebt / us-gaap_DebtInstrumentAxis = cwst_AblFacilityMember / cwst_DebtMaturityPrincipalPaymentEntityAxis = cwst_SeniorSubordinatedNotesDueTwoThousandNineteenMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |
Maturity date |  |  | Feb. 15, 2019 |  |  |  |
Abl Facility [Member] | Senior Secured Revolving Credit Facility Due Two Thousand Sixteen [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Maturity date |  |  | Mar. 18, 2016 |  |  |  |
Maine Bonds [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Maturity date |  |  |  | Jan. 01, 2025 |  |  |
Debt instrument, face amount |  | 25,000,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = cwst_MaineBondsMember |  |  |  |  |
Debt instrument interest rate |  |  |  | 6.25%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = cwst_MaineBondsMember |  |  |
Aggregate principal amount |  | 21,400,000 us-gaap_DebtAndCapitalLeaseObligations / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = cwst_MaineBondsMember |  | 21,400,000 us-gaap_DebtAndCapitalLeaseObligations / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = cwst_MaineBondsMember |  |  | 21,400,000 us-gaap_DebtAndCapitalLeaseObligations / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = cwst_MaineBondsMember
Maine Bonds [Member] | Variable Rate Bonds [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Carrying value of bonds |  |  |  | 3,600,000 us-gaap_DebtInstrumentCarryingAmount / us-gaap_DebtInstrumentAxis = cwst_VariableRateBondsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = cwst_MaineBondsMember |  |  |
Fixed Rate Bonds [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Maturity date |  |  |  | Apr. 01, 2036 |  |  |
Carrying value of bonds | 16,000,000 us-gaap_DebtInstrumentCarryingAmount / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = cwst_FixedRateBondsMember |  |  | 16,000,000 us-gaap_DebtInstrumentCarryingAmount / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = cwst_FixedRateBondsMember |  |  |
Debt instrument interest rate |  |  |  | 4.75%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = cwst_FixedRateBondsMember |  |  |
Revolver [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Carrying value of bonds |  |  |  | 131,300,000 us-gaap_DebtInstrumentCarryingAmount / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = cwst_TwoThousandElevenRevolvingCreditFacilityMember |  |  |
Senior Subordinated Notes [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Maturity date |  | Feb. 15, 2019 |  | Feb. 15, 2019 |  |  |
Debt instrument, face amount | 125,000,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorSubordinatedNotesMember | 200,000,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorSubordinatedNotesMember |  |  |  |  |
Additional increase in credit facility | 50,000,000 us-gaap_ProceedsFromLinesOfCredit / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorSubordinatedNotesMember |  |  |  |  |  |
Issued discount | 1,863,000 us-gaap_DebtInstrumentUnamortizedDiscount / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorSubordinatedNotesMember |  |  | 476,000 us-gaap_DebtInstrumentUnamortizedDiscount / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorSubordinatedNotesMember |  |  |
Carrying value of bonds |  |  |  | 325,000,000 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorSubordinatedNotesMember |  |  |
Debt instrument interest rate |  |  |  | 7.75%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorSubordinatedNotesMember |  |  |
Senior Subordinated Notes Due 2013 [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Maturity date |  | Feb. 01, 2013 |  |  |  |  |
New Hampshire Bonds [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Maturity date |  |  |  | Apr. 01, 2029 |  |  |
Carrying value of bonds |  |  |  | 11,000,000 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = cwst_NewHampshireBondsMember | 11,000,000 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = cwst_NewHampshireBondsMember |  |
Debt instrument interest rate |  |  |  | 4.00%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = cwst_NewHampshireBondsMember |  |  |
Aggregate principal amount |  |  |  |  | 5,500,000 us-gaap_DebtAndCapitalLeaseObligations / us-gaap_LongtermDebtTypeAxis = cwst_NewHampshireBondsMember |  |
Additional bond issued |  |  |  |  | 5,500,000 us-gaap_ProceedsFromIssuanceOfUnsecuredTaxExemptDebt / us-gaap_LongtermDebtTypeAxis = cwst_NewHampshireBondsMember |  |
Second Lien Notes [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Loss on debt extinguishment | 15,584,000 us-gaap_GainsLossesOnExtinguishmentOfDebt / us-gaap_LongtermDebtTypeAxis = cwst_SecondLienNotesMember |  |  |  |  |  |
Senior Secured Revolving Credit Facility Due Two Thousand Twenty [Member] | Abl Facility [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Maturity date |  |  |  | Feb. 26, 2020 |  |  |
Revolving credit facility |  |  |  | 190,000,000 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_DebtInstrumentAxis = cwst_AblFacilityMember / us-gaap_LongtermDebtTypeAxis = cwst_SeniorSecuredRevolvingCreditFacilityDueTwoThousandTwentyMember |  |  |
Additional increase in credit facility |  |  |  | 100,000,000 cwst_AdditionalRevolverCapacity / us-gaap_DebtInstrumentAxis = cwst_AblFacilityMember / us-gaap_LongtermDebtTypeAxis = cwst_SeniorSecuredRevolvingCreditFacilityDueTwoThousandTwentyMember |  |  |
Line of credit facility interest rate description |  |  |  | London Interbank Offered Rate (“LIBOR”) plus between 1.75% and 2.50% |  |  |
Debt instrument stated percentage |  |  |  | 2.25%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / us-gaap_DebtInstrumentAxis = cwst_AblFacilityMember / us-gaap_LongtermDebtTypeAxis = cwst_SeniorSecuredRevolvingCreditFacilityDueTwoThousandTwentyMember |  |  |
Senior Secured Revolving Credit Facility Due Two Thousand Twenty [Member] | Abl Facility [Member] | Minimum [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Debt instrument stated percentage |  |  |  | 1.75%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / us-gaap_DebtInstrumentAxis = cwst_AblFacilityMember / us-gaap_LongtermDebtTypeAxis = cwst_SeniorSecuredRevolvingCreditFacilityDueTwoThousandTwentyMember / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |
Senior Secured Revolving Credit Facility Due Two Thousand Twenty [Member] | Abl Facility [Member] | Maximum [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Debt instrument stated percentage |  |  |  | 2.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / us-gaap_DebtInstrumentAxis = cwst_AblFacilityMember / us-gaap_LongtermDebtTypeAxis = cwst_SeniorSecuredRevolvingCreditFacilityDueTwoThousandTwentyMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |
Senior Credit Facility [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Maturity date |  |  |  | Mar. 18, 2016 |  |  |
Revolving credit facility |  |  |  | 227,500,000 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_LongtermDebtTypeAxis = cwst_SeniorSecuredRevolvingCreditFacilityMember |  |  |
Available revolving credit facility |  |  |  | 69,133,000 us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity / us-gaap_LongtermDebtTypeAxis = cwst_SeniorSecuredRevolvingCreditFacilityMember |  |  |
Outstanding irrevocable letters of credit totaling |  |  |  | 27,067,000 us-gaap_LettersOfCreditOutstandingAmount / us-gaap_LongtermDebtTypeAxis = cwst_SeniorSecuredRevolvingCreditFacilityMember |  |  |
New York Bonds [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Maturity date |  |  |  | Dec. 18, 2044 |  |  |
Carrying value of bonds |  |  |  | 25,000,000 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = cwst_NewYorkBondsMember |  |  |
Debt instrument interest rate |  |  |  | 3.75%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = cwst_NewYorkBondsMember |  |  |
Additional bond issued |  |  |  | 15,000,000 cwst_DebtInstrumentAdditionalBorrowingsFeature / us-gaap_LongtermDebtTypeAxis = cwst_NewYorkBondsMember |  |  |
Fixed Rate Bonds [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Carrying value of bonds |  |  |  | 398,400,000 us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = cwst_FixedRateBondsMember |  |  |
Fair value of bonds |  |  |  | $ 401,861,000 us-gaap_DebtInstrumentFairValue / us-gaap_LongtermDebtTypeAxis = cwst_FixedRateBondsMember |  |  |

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