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Summary of Significant Accounting Policies - Cash and Cash Equivalents - Additional Information (Detail) | 8 Months Ended
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Dec. 31, 2014
Accounting Policies [Abstract] |
Maximum cash equivalents maturity period | Three months

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- Definition Maturity for a highly liquid investment to be considered a cash equivalent. + References No definition available. + Details
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Namespace Prefix: | cwst_
Data Type: | us-types:durationStringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration