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Development Project Charges - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Oct. 31, 2011 | Apr. 30, 2012 | Apr. 30, 2013
Collaborative Arrangements Non collaborative Arrangements And Business Acquisitions Transactions [Line Items] |  |  |
Deferred costs associated with development projects | $ 131 | $ 131 |
Deferred project costs |  | $ 1,163 | $ 1,644

X
- Definition Amount recognized as an operating expense or loss during the period to write-off the deferred costs associated with development projects no longer deemed viable. + References No definition available. + Details
Name: | cwst_AbandonedDevelopmentProjectExpense
Namespace Prefix: | cwst_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Definition Capitalized costs related to projects that are ongoing. + References No definition available. + Details
Name: | cwst_DeferredProjectCosts
Namespace Prefix: | cwst_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant