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Summary of Significant Accounting Policies - Derivatives and Hedging - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
8 Months Ended 12 Months Ended 1 Months Ended
Dec. 31, 2014
Agreement
Dec. 31, 2013
Apr. 30, 2014
Apr. 30, 2013
Feb. 28, 2015
Jan. 15, 2013
Summary Of Significant Accounting Policies [Line Items]            
Number of interest rate derivative agreements 2us-gaap_DerivativeNumberOfInstrumentsHeld          
Derivative liability notional amount $ 150,000us-gaap_DerivativeLiabilityNotionalAmount     $ 75,000us-gaap_DerivativeLiabilityNotionalAmount    
LIBOR base rate 1.40%us-gaap_DerivativeFixedInterestRate          
Derivative Instrument maturity term Mar. 15, 2016          
Loss on derivative instruments (225)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet 69us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet (280)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet (4,512)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet    
Interest Rate Swap [Member]            
Summary Of Significant Accounting Policies [Line Items]            
Obligation recorded in other accrued liabilities and other long-term liabilities 1,668us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
         
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Interest Rate Swap [Member]            
Summary Of Significant Accounting Policies [Line Items]            
Loss on derivative instruments       3,626us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember
   
Subsequent Event [Member]            
Summary Of Significant Accounting Policies [Line Items]            
Settlement of forward starting interest rate derivative agreements         $ 830cwst_DerivativeSettlementOfForwardStartingInterestRateSwapAgreement
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
 
Second Lien Notes [Member]            
Summary Of Significant Accounting Policies [Line Items]            
Derivative instrument interest rate           11.00%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_FinancialInstrumentAxis
= cwst_SecondLienNotesMember