ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Accumulated Other Comprehensive Income (loss) by Component (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent [Roll Forward]
Balance as of Beginning of Period	$ (65,282)
OCI Before Reclassifications	1,700	$ 200
Amounts Reclassified from AOCL	1,500	1,400
Net OCI	3,141	1,669
Balance as of End of Period	(62,141)
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent [Roll Forward]
Balance as of Beginning of Period	(65,300)	(66,800)
Balance as of End of Period	(62,100)	(65,200)
Qualified Cash Flow Hedging Instruments [Member]
AOCI Attributable to Parent [Roll Forward]
Balance as of Beginning of Period	(8,200)	(10,300)
OCI Before Reclassifications	0	0
Amounts Reclassified from AOCL	500	500
Net OCI	500	500
Balance as of End of Period	(7,700)	(9,800)
Unrealized Gains/(Losses) on Marketable Securities [Member]
AOCI Attributable to Parent [Roll Forward]
Balance as of Beginning of Period	400	(1,900)
OCI Before Reclassifications	1,700	200
Amounts Reclassified from AOCL	0	0
Net OCI	1,700	200
Balance as of End of Period	2,100	(1,700)
Defined Benefit Plans [Member]
AOCI Attributable to Parent [Roll Forward]
Balance as of Beginning of Period	(57,500)	(54,600)
OCI Before Reclassifications	0	0
Amounts Reclassified from AOCL	1,000	900
Net OCI	1,000	900
Balance as of End of Period	$ (56,500)	$ (53,700)