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Basis of Presentation - Additional Information (Detail)	8 Months Ended
	Dec. 31, 2014 Segment
Segment Reporting Information [Line Items]
Operating segments	4us-gaap_NumberOfOperatingSegments
Eastern Region [Member]
Segment Reporting Information [Line Items]
Operating segments	1us-gaap_NumberOfOperatingSegments / us-gaap_StatementBusinessSegmentsAxis = cwst_EasternRegionMember
Western Region [Member]
Segment Reporting Information [Line Items]
Operating segments	1us-gaap_NumberOfOperatingSegments / us-gaap_StatementBusinessSegmentsAxis = cwst_WesternRegionMember
Recycling [Member]
Segment Reporting Information [Line Items]
Operating segments	1us-gaap_NumberOfOperatingSegments / us-gaap_StatementBusinessSegmentsAxis = cwst_RecyclingMember
Other [Member]
Segment Reporting Information [Line Items]
Operating segments	1us-gaap_NumberOfOperatingSegments / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember

X

- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

X

- Details

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

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=cwst_RecyclingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=cwst_WesternRegionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=us-gaap_AllOtherSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: