LEASES - Narrative (Details)	9 Months Ended
Sep. 30, 2020 Agreement
Leases [Abstract]
Number of landfill operation and management agreements	3

Number of Landfill Operation and Management Agreements Entered Into

No definition available.

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