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Stockholders' Equity - Summary of Grant Activity for Stock Options, Restricted Stock Units, Performance Stock Units and Restricted Stock Awards (Parenthetical) (Detail) (Performance Stock Units [Member]) | Apr. 30, 2013
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Performance Stock Units [Member] |
Schedule Of Stock Option Activity [Line Items] |
Performance stock units, percentage of attainment level | 100.00%

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- Details
Name: | cwst_ScheduleOfStockOptionActivityLineItems
Namespace Prefix: | cwst_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The attainment level for performance stock units included in the roll forward. + References No definition available. + Details
Name: | cwst_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardTargetPerformanceRate
Namespace Prefix: | cwst_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant