DEBT - Narrative - Credit Facility (Details) - USD ($)	1 Months Ended
Sep. 30, 2024	Jun. 30, 2025
Line of Credit Facility [Line Items]
Letters of credit outstanding		$ 26,307,000
Line of Credit \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit drawn		0
Credit Facility
Line of Credit Facility [Line Items]
Additional revolver capacity	$ 200,000,000
Facility term	5 years
Variable rate adjustment	0.04%
Commitment fee percentage, adjustment	0.01%
Floor interest rate	0.00%
Interest rate, annual increase upon payment default	2.00%
Interest rate, annual increase upon other event of default	2.00%
Credit Facility \| Minimum
Line of Credit Facility [Line Items]
Commitment fee percentage	0.20%
Credit Facility \| Maximum
Line of Credit Facility [Line Items]
Commitment fee percentage	0.40%
Credit Facility \| Secured Debt
Line of Credit Facility [Line Items]
Aggregate principal amount issued	$ 800,000,000
Credit Facility \| Line of Credit \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Credit facility, maximum borrowing capacity	700,000,000
Letters of credit sublimit	$ 155,000,000
Remaining capacity		$ 673,693,000
Credit Facility \| Line of Credit \| Letter of Credit
Line of Credit Facility [Line Items]
Fronting fee	0.25%

Debt Instrument, Floor Interest Rate

No definition available.

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- Definition

Debt Instrument, Interest Rate, Annual Increase, Upon Other Event Of Default

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Interest Rate, Annual Increase, Upon Payment Default

+ References

No definition available.

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- Definition

Debt Instrument, Variable Rate Adjustment

+ References

No definition available.

+ Details

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Balance Type:	na
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- Definition

Sublimit to the amount of letters of credit allowed under credit agreement.

+ References

No definition available.

+ Details

Name:	cwst_LettersOfCreditSublimit
Namespace Prefix:	cwst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of additional optional borrowing capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	cwst_LineOfCreditFacilityAdditionalBorrowingCapacity
Namespace Prefix:	cwst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line of Credit Facility, Fronting Fee Percentage

+ References

No definition available.

+ Details

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Namespace Prefix:	cwst_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of Credit Facility, Unused Capacity, Commitment Fee Percentage, Adjustment

+ References

No definition available.

+ Details

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Namespace Prefix:	cwst_
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Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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+ Details

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

- 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

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

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+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

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+ Details

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

- 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

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+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
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+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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Period Type:	duration

- Details

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- Details

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Balance Type:
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- Details

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- Details

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- Details

Name:	srt_RangeAxis=srt_MaximumMember
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- Details

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- Details

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