ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Attributable to Parent [Roll Forward]
OCI Before Reclassifications	$ (700)	$ 200
Amounts Reclassified from AOCI	1,900	1,800
Net OCI	1,188	1,948
Total
AOCI Attributable to Parent [Roll Forward]
Balance	(76,400)	(65,100)
Net OCI	1,188	1,948
Balance	(75,200)	(63,100)
Qualified Cash Flow Hedging Instruments
AOCI Attributable to Parent [Roll Forward]
Balance	(1,400)	(3,000)
OCI Before Reclassifications	0	0
Amounts Reclassified from AOCI	400	200
Net OCI	400	200
Balance	(1,000)	(2,800)
Unrealized Gains/(Losses) on Marketable Securities
AOCI Attributable to Parent [Roll Forward]
Balance	1,100	700
OCI Before Reclassifications	(700)	200
Amounts Reclassified from AOCI	0	0
Net OCI	(700)	200
Balance	400	900
Defined Benefit Plans
AOCI Attributable to Parent [Roll Forward]
Balance	(76,100)	(62,800)
OCI Before Reclassifications	0	0
Amounts Reclassified from AOCI	1,500	1,600
Net OCI	1,500	1,600
Balance	$ (74,600)	$ (61,200)