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COMMITMENTS AND CONTINGENCIES - Schedule of Environmental Liability Associated with Southbridge Landfill (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Accrual for Environmental Loss Contingencies [Roll Forward] |  |
Ending balance | $ 11,694 |
Southbridge Landfill |  |
Accrual for Environmental Loss Contingencies [Roll Forward] |  |
Beginning balance | 0 | $ 0
Accretion expense | 82 | 0
Obligations incurred | 6,379 | 0
Obligations settled | (525) | 0
Ending balance | $ 5,936 | $ 0

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