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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
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

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Data Type:	xbrli:stringItemType
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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

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Namespace Prefix:	cwst_
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Balance Type:	na
Period Type:	instant