Debt Instrument, Covenant Compliance, Net Leverage Ratio

No definition available.

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- Definition

Amount of additional optional borrowing capacity under the credit facility.

+ References

No definition available.

+ Details

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ 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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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

No definition available.

+ Details

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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

No definition available.

+ 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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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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

+ Details

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

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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DEBT - Credit Facility (Details)	12 Months Ended
DEBT - Credit Facility (Details)	Dec. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)
Line of Credit Facility [Line Items]
Additional revolver capacity		$ 125,000,000
Secured Debt \| Term Loan Facility \| Line of Credit
Line of Credit Facility [Line Items]
Aggregate principal amount issued		350,000,000
Secured Debt \| Term Loan B Facility
Line of Credit Facility [Line Items]
Aggregate principal amount issued		350,000,000
Facility term	5 years
Net leverage ratio	2.25
Secured Debt \| Term Loan B Facility \| LIBOR \| Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.75%
Secured Debt \| Term Loan B Facility \| LIBOR \| Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.25%
Revolving Credit Facility \| Revolving Credit Facility \| Line of Credit
Line of Credit Facility [Line Items]
Credit facility maximum		200,000,000
Line of Credit \| Refinanced Revolving Credit Facility \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Credit facility maximum		$ 160,000,000
Remaining capacity	$ 173,575,000
Line of Credit \| Refinanced Revolving Credit Facility \| Letter of Credit
Line of Credit Facility [Line Items]
Outstanding irrevocable letters of credit totaling	$ 26,425,000