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Summary of Significant Accounting Policies - Estimated Useful Lives of Assets (Detail) | 12 Months Ended
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Apr. 30, 2013
Minimum [Member] | Buildings [Member] |
Depreciation Amortization Impairment [Line Items] |
Property plant and equipment, estimated useful life | 25 years
Minimum [Member] | Machinery and equipment [Member] |
Depreciation Amortization Impairment [Line Items] |
Property plant and equipment, estimated useful life | 5 years
Minimum [Member] | Rolling stock [Member] |
Depreciation Amortization Impairment [Line Items] |
Property plant and equipment, estimated useful life | 5 years
Minimum [Member] | Containers [Member] |
Depreciation Amortization Impairment [Line Items] |
Property plant and equipment, estimated useful life | 5 years
Minimum [Member] | Furniture and Fixtures [Member] |
Depreciation Amortization Impairment [Line Items] |
Property plant and equipment, estimated useful life | 3 years
Maximum [Member] | Buildings [Member] |
Depreciation Amortization Impairment [Line Items] |
Property plant and equipment, estimated useful life | 30 years
Maximum [Member] | Machinery and equipment [Member] |
Depreciation Amortization Impairment [Line Items] |
Property plant and equipment, estimated useful life | 10 years
Maximum [Member] | Rolling stock [Member] |
Depreciation Amortization Impairment [Line Items] |
Property plant and equipment, estimated useful life | 10 years
Maximum [Member] | Containers [Member] |
Depreciation Amortization Impairment [Line Items] |
Property plant and equipment, estimated useful life | 12 years
Maximum [Member] | Furniture and Fixtures [Member] |
Depreciation Amortization Impairment [Line Items] |
Property plant and equipment, estimated useful life | 8 years

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- Details
Name: | cwst_DepreciationAmortizationImpairmentLineItems
Namespace Prefix: | cwst_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration