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