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Stockholders' Equity - Summary of Restricted Stock, Restricted Stock Unit and Performance Stock Unit Activity (Parenthetical) (Detail) (Performance Stock Units [Member])
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Performance Stock Units [Member]
 
Schedule Of Restricted Stock Restricted Stock Unit And Performance Stock Unit Activity [Line Items]  
Performance stock units, percentage of attainment level 100.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_StatementClassOfStockAxis
= cwst_PerformanceShareUnitsMember
Common stock additional issue 242cwst_AdditionalSharesIssuedMaximumAttainmentLevel
/ us-gaap_StatementClassOfStockAxis
= cwst_PerformanceShareUnitsMember