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Business Combinations - Schedule of Purchase Price Paid for Acquisitions (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Apr. 30, 2014
Business Combinations [Abstract] |
Gain on settlement of acquisition related contingent consideration | $ 1,058

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- Definition The gain or loss recorded as a result of the settlement of acquisition related contingent consideration. + References No definition available. + Details
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Namespace Prefix: | cwst_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
Name: | us-gaap_BusinessCombinationsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration