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Summary of Significant Accounting Policies - Goodwill and Intangible Assets - Additional Information (Detail) (Maximum [Member])	8 Months Ended
	Dec. 31, 2014
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Intangible assets, useful life	10 years

X

- Details

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Namespace Prefix:	cwst_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration