STOCKHOLDERS' EQUITY (AOCI) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss)
Total after-tax amount	$ 759,206	$ 763,043	$ 721,755	$ 717,682
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss)
Total pre-tax amount	(3,078)	260
Total after-tax amount	(2,264)	203	(12,388)	(14,238)
Unrecognized Net Periodic Benefit Credit (cost)
Accumulated Other Comprehensive Income (Loss)
Total pre-tax amount	2,831	2,898
Total after-tax amount	2,102	2,152	(10,792)	(12,749)
Interest Rate Swap
Accumulated Other Comprehensive Income (Loss)
Total pre-tax amount	(1,912)	(563)
Total after-tax amount	(1,413)	(416)	259	591
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss)
Total pre-tax amount	(3,997)	(2,075)
Total after-tax amount	$ (2,953)	$ (1,533)	$ (1,855)	$ (2,080)