XML 64 R53.htm IDEA: XBRL DOCUMENT v3.10.0.1

COMMITMENTS AND CONTINGENCIES - Additional Information (Detail)			1 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
	Jul. 17, 2018 USD ($)	Apr. 28, 2017 USD ($)	Nov. 30, 2016 basin	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2018 USD ($)	Apr. 26, 2017 USD ($)	Jan. 29, 2016	Apr. 30, 2011 USD ($)	May 31, 2009 USD ($)	Dec. 20, 2000 a
Loss Contingencies [Line Items]
Number of storm water basins | basin			2
Litigation settlement, future cash payments							$ 850,000
Ancillary services, period							5 years
Litigation settlement, total cash and services							$ 1,200,000
Litigation settlement, amount awarded form other party				$ 10,000,000	$ 0		10,000,000	$ 0
Litigation settlement received						$ 0	$ 992,000
Southbridge Landfill
Loss Contingencies [Line Items]
Risk free interest percentage rate				2.60%			2.60%
Reserve for probable loss				$ 366,000			$ 366,000
Litigation settlement received							$ 3,506,000	$ 0
Potsdam Environmental Remediation Liability
Loss Contingencies [Line Items]
Risk free interest percentage rate				1.50%			1.50%
Scrap yard and solid waste transfer station (in acres) | a														25
Undiscounted costs preferred remedies												$ 12,130,000	$ 10,219,000
Remediation activities, participant share percentage											15.00%
Maximum | Southbridge Landfill | Scenario, Forecast
Loss Contingencies [Line Items]
Loss on contract termination									$ 2,199,000
21E Settlement and Water System Construction Funding Agreement | Bonds
Loss Contingencies [Line Items]
Bond period		20 years
21E Settlement and Water System Construction Funding Agreement | Bonds | Maximum
Loss Contingencies [Line Items]
Amount of costs		$ 5,000,000
Notice of Intent to Sue under the Resource Conservation and Recovery Act
Loss Contingencies [Line Items]
Estimate of possible loss										$ 5,000,000
Notice of Intent to Sue under the Resource Conservation and Recovery Act | MADEP and Casella Waste System
Loss Contingencies [Line Items]
Estimate of possible loss										$ 10,000,000
Steadfast Insurance Company
Loss Contingencies [Line Items]
Litigation settlement, amount awarded form other party	$ 10,000,000
Litigation settlement received	$ 10,000,000

X

- Definition

Ancillary Services, Period

+ References

No definition available.

+ Details

Name:	cwst_AncillaryServicesPeriod
Namespace Prefix:	cwst_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Number of Storm Water Basins

+ References

No definition available.

+ Details

Name:	cwst_NumberofStormWaterBasins
Namespace Prefix:	cwst_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Percentage participation in onsite remediation activities.

+ References

No definition available.

+ Details

Name:	cwst_PercentageParticipationInOnsiteRemediationActivities
Namespace Prefix:	cwst_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Acreage of scrap yard owned by WSI.

+ References

No definition available.

+ Details

Name:	cwst_ScrapYardAndSolidWasteTransferStation
Namespace Prefix:	cwst_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Estimated undiscounted remediation costs.

+ References

No definition available.

+ Details

Name:	cwst_UndiscountedCostsPreferredRemedies
Namespace Prefix:	cwst_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Rate applied to the undiscounted amount of environmental loss contingencies to arrive at the present value recorded as of the balance sheet date.

+ 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 S99
-Paragraph 1
-Subparagraph (SAB Topic 5.Y.Q1)
-URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Total anticipated costs associated with remediation, site restoration, postclosure, monitoring commitments, or other exit costs that may occur on the sale, disposal, or abandonment of a particular property resulting from unanticipated contamination of the assets.

+ 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.Q4)
-URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751

+ Details

Name:	us-gaap_EnvironmentalExitCostsAnticipatedCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount awarded from other party in judgment or settlement of litigation.

+ References

No definition available.

+ Details

Name:	us-gaap_LitigationSettlementAmountAwardedFromOtherParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount awarded to other party in judgment or settlement of litigation.

+ References

No definition available.

+ Details

Name:	us-gaap_LitigationSettlementAmountAwardedToOtherParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

X

- Definition

Amount of loss contingency liability.

+ References

Reference 1: 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=82911808&loc=d3e14326-108349

+ Details

Name:	us-gaap_LossContingencyAccrualAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14557-108349

+ Details

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

X

- Definition

The loss recognized on termination of a contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 912
-SubTopic 275
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84167019&loc=d3e54681-109401

+ Details

Name:	us-gaap_LossOnContractTermination
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

The amount of cash paid for the settlement of litigation or for other legal issues during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585

+ Details

Name:	us-gaap_PaymentsForLegalSettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of cash inflow for proceeds from settlement of insurance claim, classified as investing activities. Excludes insurance settlement classified as operating activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 21B
-URI http://asc.fasb.org/extlink&oid=98514028&loc=SL94080549-108585

+ Details

Name:	us-gaap_ProceedsFromInsuranceSettlementInvestingActivities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=cwst_SouthbridgeLandfillMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=cwst_PotsdamEnvironmentalLiabilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=cwst_A21ESettlementandWaterSystemConstructionFundingAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_BondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_LitigationCaseAxis=cwst_NoticeofIntenttoSueundertheResourceConservationandRecoveryActMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	dei_LegalEntityAxis=cwst_MassachusettsDepartmentofEnvironmentalProtectionMADEPandCasellaWasteSystemsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_LitigationCaseAxis=cwst_SteadfastInsuranceCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: