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Commitments and Contingencies - Schedule of Environmental Liability Associated with Potsdam (Detail) (Potsdam Environmental Remediation Liability [Member], USD $) In Thousands, unless otherwise specified | 3 Months Ended |
--- | --- | ---
Mar. 31, 2014 | Mar. 31, 2015 | Dec. 31, 2014
Site Contingency [Line Items] |  |  |
Beginning balance | $ 5,421 us-gaap_AccrualForEnvironmentalLossContingencies |  | $ 5,142 us-gaap_AccrualForEnvironmentalLossContingencies
Obligations settled | (26)us-gaap_AccrualForEnvironmentalLossContingenciesPayments |  |
Ending balance | 5,429 us-gaap_AccrualForEnvironmentalLossContingencies | 5,162 us-gaap_AccrualForEnvironmentalLossContingencies | 5,142 us-gaap_AccrualForEnvironmentalLossContingencies
Accretion Expense [Member] |  |  |
Site Contingency [Line Items] |  |  |
Accretion expense | $ 34 us-gaap_AccrualForEnvironmentalLossContingenciesProvisionForNewLosses / us-gaap_EnvironmentalRemediationSiteAxis = cwst_PotsdamEnvironmentalLiabilityMember / us-gaap_NatureOfExpenseAxis = cwst_EnvironmentalAccretionExpenseMember | $ 20 us-gaap_AccrualForEnvironmentalLossContingenciesProvisionForNewLosses / us-gaap_EnvironmentalRemediationSiteAxis = cwst_PotsdamEnvironmentalLiabilityMember / us-gaap_NatureOfExpenseAxis = cwst_EnvironmentalAccretionExpenseMember |

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- Definition Total costs accrued as of the balance sheet date for environmental loss contingencies. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The aggregate amount disbursed during the reporting period to settle environmental loss contingencies. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q2) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | debit
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- Definition The amount added to the accrual for newly incurred environmental loss contingencies. These additions include remediation expense and interest accretion. These additions do not relate to changes in the environmental accrual related to a business acquisition or divestiture, to currency movements, or revisions in previously existing estimates. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q2) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + Details
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Namespace Prefix: | us-gaap_
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Period Type: | duration

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