ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent [Roll Forward]
OCI Before Reclassifications					$ (1,200)	$ 3,700
Amounts Reclassified from AOCI					3,700	2,700
Other Comprehensive Income (Loss), Net of Tax	$ 553	$ 1,948	$ 4,163	$ 2,196	2,501	6,359
Total
AOCI Attributable to Parent [Roll Forward]
Balance		(65,100)		(60,000)	(65,100)	(60,000)
Other Comprehensive Income (Loss), Net of Tax	553	1,948	4,163	2,196
Balance	(62,600)		(53,600)		(62,600)	(53,600)
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					600	600
Other Comprehensive Income (Loss), Net of Tax					600	600
Balance	(2,400)		(3,800)		(2,400)	(3,800)
Unrealized Gains on Marketable Securities
AOCI Attributable to Parent [Roll Forward]
Balance		700		(500)	700	(500)
OCI Before Reclassifications					400	1,100
Amounts Reclassified from AOCI					0	0
Other Comprehensive Income (Loss), Net of Tax					400	1,100
Balance	1,100		600		1,100	600
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					3,100	2,100
Other Comprehensive Income (Loss), Net of Tax					1,500	4,700
Balance	$ (61,300)		$ (50,400)		$ (61,300)	$ (50,400)