OTHER COMPREHENSIVE INCOME (Changes in Accumulated Other Comprehensive Income, Net of Tax) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning balance	$ (197,738)	$ (172,215)	$ (179,095)
Other comprehensive income (loss) before reclassifications	(8,313)	(26,892)	2,289
Amounts reclassified from AOCI	24,746	1,369	4,591
Other comprehensive income (loss)	16,433	(25,523)	6,880
AOCI, Ending balance	(181,305)	(197,738)	(172,215)
Reclassification Adjustment for Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning balance	(10,953)	(11,180)	(13,902)
Other comprehensive income (loss) before reclassifications	(14,679)	0	2,496
Amounts reclassified from AOCI	1,689	227	226
Other comprehensive income (loss)	(12,990)	227	2,722
AOCI, Ending balance	(23,943)	(10,953)	(11,180)
Amortization of Pension and Postretirement Plan Actuarial Loss and Prior Service Cost [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning balance	(186,785)	(161,035)	(165,193)
Other comprehensive income (loss) before reclassifications	6,366	(26,892)	(207)
Amounts reclassified from AOCI	23,057	1,142	4,365
Other comprehensive income (loss)	29,423	(25,750)	4,158
AOCI, Ending balance	$ (157,362)	$ (186,785)	(161,035)
Scenario, Previously Reported [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning balance			(149,466)
Scenario, Previously Reported [Member] | Reclassification Adjustment for Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning balance			(11,438)
Scenario, Previously Reported [Member] | Amortization of Pension and Postretirement Plan Actuarial Loss and Prior Service Cost [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning balance			(138,028)
Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning balance			(29,629)
Revision of Prior Period, Accounting Standards Update, Adjustment [Member] | Reclassification Adjustment for Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning balance			(2,464)
Revision of Prior Period, Accounting Standards Update, Adjustment [Member] | Amortization of Pension and Postretirement Plan Actuarial Loss and Prior Service Cost [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning balance			$ (27,165)