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Development Project Charge - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
	Jan. 31, 2014	Jan. 31, 2014	Apr. 30, 2013
Research And Development [Abstract]
Deferred costs associated with development projects	$ 1,440	$ 1,440
Deferred project costs	$ 0	$ 0	$ 1,644

X

- Definition

Amount recognized as an operating expense or loss during the period to write-off the deferred costs associated with development projects no longer deemed viable.

+ References

No definition available.

+ Details

Name:	cwst_AbandonedDevelopmentProjectExpense
Namespace Prefix:	cwst_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Gross amount of other deferred costs capitalized at the end of the reporting period. Does not include deferred finance costs or deferred acquisition costs of insurance companies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.17)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_OtherDeferredCostsGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

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