STOCKHOLDERS' EQUITY (AOCI) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Loss
Total after-tax amount	$ 763,626	$ 743,159	$ 721,755	$ 717,682	$ 705,091	$ 668,515	$ 665,474	$ 651,462
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Loss
Total pre-tax amount	(10,292)			(13,836)
Total after-tax amount	(7,630)	$ (12,429)	$ (12,388)	(14,238)	(22,620)	$ (17,842)	$ (20,078)	(20,574)
Unrecognized Net Periodic Benefit Costs
Accumulated Other Comprehensive Loss
Total pre-tax amount	(7,068)			(11,821)
Total after-tax amount	(5,249)			(12,749)	(22,357)			(19,715)
Interest Rate Swap, 2019
Accumulated Other Comprehensive Loss
Total pre-tax amount	(822)
Total after-tax amount	(607)			591
Interest Rate Swap, 2018
Accumulated Other Comprehensive Loss
Total pre-tax amount				801
Total after-tax amount				591	1,301			292
Foreign Currency Translation
Accumulated Other Comprehensive Loss
Total pre-tax amount	(2,402)			(2,816)
Total after-tax amount	$ (1,774)			$ (2,080)	$ (1,564)			$ (1,151)