CLOSURE AND POST-CLOSURE OBLIGATIONS - Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Changes to reported closure and post-closure obligations
Closure and post-closure obligations, beginning of period	$ 79,056	$ 78,363
Accretion expense	1,133	2,258	$ 2,155
Payments	(305)	(775)
Adjustments	35	73
Closure and post-closure obligations, end of period	79,919	79,919
Less current portion	(2,231)	(2,231)		$ (2,266)
Long-term portion	$ 77,688	$ 77,688		$ 76,097

The amount of estimated costs accrued as of the balance sheet date to comply with regulatory requirements pertaining to the retirement of a waste management facility (such as a landfill or waste treatment facility). Represents the portion that will be paid within one year or the normal operating cycle, if longer.

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The estimated amount of costs required as of the balance sheet date to comply with regulatory requirements pertaining to the retirement of a waste management facility, which will be paid after one year or beyond the normal operating cycle, if longer.

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The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

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Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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