COMMITMENTS AND CONTINGENCIES - Southbridge Landfill Environmental Remediation Liability (Details) - Southbridge Landfill - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	$ 5,173	$ 5,936
Accretion expense	94	116
Obligations settled	(556)	(612)
Ending balance	$ 4,711	$ 5,440

Total costs accrued as of the balance sheet date for environmental loss contingencies.

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Amount of expense for newly incurred environmental loss contingencies. Includes, but is not limited to, remediation expense and interest accretion.

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Amount of cash outflow to settle environmental loss contingencies.

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