ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
AOCI Attributable to Parent [Roll Forward]
OCI Before Reclassifications							$ (1,300)	$ 3,900
Amounts Reclassified from AOCI							6,000	4,100
Other Comprehensive Income (Loss), Net of Tax	$ 2,161	$ 553	$ 1,948	$ 1,624	$ 4,163	$ 2,196	4,662	7,983
Total
AOCI Attributable to Parent [Roll Forward]
Balance			(65,100)			(60,000)	(65,100)	(60,000)
Other Comprehensive Income (Loss), Net of Tax	2,161	$ 553	1,948	1,624	$ 4,163	2,196
Balance	(60,400)			(52,000)			(60,400)	(52,000)
Qualified Cash Flow Hedging Instruments
AOCI Attributable to Parent [Roll Forward]
Balance			(3,000)			(4,400)	(3,000)	(4,400)
OCI Before Reclassifications							0	0
Amounts Reclassified from AOCI							1,200	900
Other Comprehensive Income (Loss), Net of Tax							1,200	900
Balance	(1,800)			(3,500)			(1,800)	(3,500)
Unrealized Gains on Marketable Securities
AOCI Attributable to Parent [Roll Forward]
Balance			700			(500)	700	(500)
OCI Before Reclassifications							300	1,300
Amounts Reclassified from AOCI							0	0
Other Comprehensive Income (Loss), Net of Tax							300	1,300
Balance	1,000			800			1,000	800
Defined Benefit Plans
AOCI Attributable to Parent [Roll Forward]
Balance			$ (62,800)			$ (55,100)	(62,800)	(55,100)
OCI Before Reclassifications							(1,600)	2,600
Amounts Reclassified from AOCI							4,800	3,200
Other Comprehensive Income (Loss), Net of Tax							3,200	5,800
Balance	$ (59,600)			$ (49,300)			$ (59,600)	$ (49,300)