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COMMITMENTS AND CONTINGENCIES - Narrative (Detail) plantiff in Thousands, $ in Thousands |  |  |  | 3 Months Ended | 9 Months Ended |  |  |  |  |  |  |  |
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Dec. 01, 2020 USD ($) | Sep. 17, 2019 plantiff | Apr. 28, 2017 USD ($) | Sep. 30, 2020 USD ($) | Sep. 30, 2020 USD ($) | Sep. 30, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Apr. 26, 2017 USD ($) | Jan. 29, 2016 | Apr. 30, 2011 USD ($) | May 31, 2009 USD ($) | Dec. 20, 2000 a
Southbridge Landfill |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Loss contingency, settlement awarded |  |  |  | $ 2,000 | $ 2,000 |  |  |  |  |  |  |  |
Risk free interest (as a percent) |  |  |  |  |  | 2.60% |  |  |  |  |  |  |
Environmental remediation liability |  |  |  | $ 4,233 | $ 4,233 | $ 4,062 | $ 4,261 | $ 4,596 |  |  |  |  |
Potsdam Environmental Remediation |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Risk free interest (as a percent) |  |  |  |  |  | 1.90% |  |  |  |  |  |  |
Scrap yard and solid waste transfer station (in acres) | a |  |  |  |  |  |  |  |  |  |  |  |  | 25
Undiscounted costs preferred remedies |  |  |  |  |  |  |  |  |  |  | $ 12,130 | $ 10,219 |
Remediation activities, participant share (as a percent) |  |  |  |  |  |  |  |  |  | 15.00% |  |  |
Environmental remediation liability |  |  |  |  |  | $ 939 | $ 939 |  |  |  |  |  |
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] |  |  |  |  |  |  |  |  |  |  |  |  |
Anticipated cost |  |  | $ 4,089 |  |  |  |  |  |  |  |  |  |
Notice of Intent to Sue under the Resource Conservation and Recovery Act |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Estimate of possible loss |  |  |  |  |  |  |  |  | $ 5,000 |  |  |  |
Notice of Intent to Sue under the Resource Conservation and Recovery Act | MADEP and Casella Waste Systems |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Estimate of possible loss |  |  |  |  |  |  |  |  | $ 10,000 |  |  |  |
Ontario County, New York Class Action Litigation |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of citizens seeking damages | plantiff |  | 1 |  |  |  |  |  |  |  |  |  |  |
Loss contingency, settlement awarded | $ 750 |  |  |  |  |  |  |  |  |  |  |  |
Estimate of possible loss | $ 900 |  |  |  |  |  |  |  |  |  |  |  |

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