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Restricted Cash / Restricted Assets - Summary of Restricted Cash / Restricted Asset (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Apr. 30, 2014	Apr. 30, 2013
Current:
Restricted cash / restricted assets	$ 76us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue	$ 76us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue	$ 76us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue
Non Current:
Restricted cash / restricted assets	6,632us-gaap_RestrictedCashAndInvestmentsNoncurrent	681us-gaap_RestrictedCashAndInvestmentsNoncurrent	545us-gaap_RestrictedCashAndInvestmentsNoncurrent
Landfills [Member]
Current:
Restricted cash / restricted assets	76us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_LandfillMember	76us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_LandfillMember	76us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_LandfillMember
Non Current:
Restricted cash / restricted assets	813us-gaap_RestrictedCashAndInvestmentsNoncurrent / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_LandfillMember	681us-gaap_RestrictedCashAndInvestmentsNoncurrent / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_LandfillMember	545us-gaap_RestrictedCashAndInvestmentsNoncurrent / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_LandfillMember
Capital Projects [Member]
Non Current:
Restricted cash / restricted assets	$ 5,819us-gaap_RestrictedCashAndInvestmentsNoncurrent / us-gaap_PropertyPlantAndEquipmentByTypeAxis = cwst_CapitalProjectsMember

X

- Definition

The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. For a classified balance sheet represents the current portion only (the noncurrent portion has a separate concept); there is a separate and distinct element for unclassified presentations.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 1

-Article 5



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.1)

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

+ Details

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- Details

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X

- Definition

The noncurrent cash, cash equivalents and investments that is restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits classified as long-term; that is not expected to be released from such existing restrictions within one year of the balance sheet date or operating cycle, whichever is longer. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. Includes noncurrent cash equivalents and investments that are similarly restricted as to withdrawal, usage or disposal.

+ References

No definition available.

+ Details

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- Details

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- Details

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