| Cover Page Document | Feb. 18, 2021 |
| Cover [Abstract] | |
| Title of 12(b) Security | Class A common stock, $0.01 par value per share |
| Entity Address, Address Line One | 25 Greens Hill Lane, |
| Entity Central Index Key | 0000911177 |
| Amendment Flag | false |
| Written Communications | false |
| Entity Emerging Growth Company | false |
| Document Type | 8-K |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 000-23211 |
| Entity Tax Identification Number | 03-0338873 |
| Entity Address, Postal Zip Code | 05701 |
| Document Period End Date | Feb. 18, 2021 |
| Entity Registrant Name | Casella Waste Systems, Inc. |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| City Area Code | 802 |
| Local Phone Number | 775-0325 |
| Entity Address, City or Town | Rutland, |
| Entity Address, State or Province | VT |
| Trading Symbol | CWST |
| Security Exchange Name | NASDAQ |
