ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
AOCI Attributable to Parent [Roll Forward]
OCI Before Reclassifications					$ (2,900)	$ (1,200)
Amounts Reclassified from AOCI					5,000	3,700
Net OCI	$ 881	$ 1,188	$ 553	$ 1,948	2,069	2,501
Total
AOCI Attributable to Parent [Roll Forward]
Beginning balance		(76,400)		(65,100)	(76,400)	(65,100)
Net OCI	881	1,188	553	1,948
Ending balance	(74,300)		(62,600)		(74,300)	(62,600)
Qualified Cash Flow Hedging Instruments
AOCI Attributable to Parent [Roll Forward]
Beginning balance		(1,400)		(3,000)	(1,400)	(3,000)
OCI Before Reclassifications					0	0
Amounts Reclassified from AOCI					900	600
Net OCI					900	600
Ending balance	(500)		(2,400)		(500)	(2,400)
Unrealized Gains/(Losses) on Marketable Securities
AOCI Attributable to Parent [Roll Forward]
Beginning balance		1,100		700	1,100	700
OCI Before Reclassifications					(500)	400
Amounts Reclassified from AOCI					0	0
Net OCI					(500)	400
Ending balance	600		1,100		600	1,100
Defined Benefit Plans
AOCI Attributable to Parent [Roll Forward]
Beginning balance		$ (76,100)		$ (62,800)	(76,100)	(62,800)
OCI Before Reclassifications					(2,400)	(1,600)
Amounts Reclassified from AOCI					4,100	3,100
Net OCI					1,700	1,500
Ending balance	$ (74,400)		$ (61,300)		$ (74,400)	$ (61,300)