INCOME TAXES (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Provision for doubtful accounts	$ 10,305	$ 8,949
Closure, post-closure and remedial liabilities	28,665	26,960
Operating lease liabilities	38,151	40,879
Accrued expenses	16,797	17,602
Accrued compensation and benefits	11,372	7,155
Net operating loss carryforwards	50,433	50,824
Tax credit carryforwards	14,471	16,909
Interest rate swap liability	10,089	6,252
Stock-based compensation	3,040	2,435
Other	5,553	8,342
Total deferred tax assets	188,876	186,307
Deferred tax liabilities:
Property, plant and equipment	(194,604)	(184,594)
Operating lease right-of-use assets	(38,018)	(40,985)
Permits and other intangible assets	(95,492)	(98,654)
Prepaid expenses	(9,660)	(9,694)
Total deferred tax liabilities	(337,774)	(333,927)
Total net deferred tax liability before valuation allowance	(148,898)	(147,620)
Less valuation allowance	(77,044)	(83,643)
Net deferred tax liabilities	(225,942)	$ (231,263)
State and local operating loss carryforwards	193,200
Federal operating loss carryforwards	16,800
Foreign operating loss carryforwards	151,500
Foreign tax credit carryforwards	$ 14,100