STOCKHOLDERS' EQUITY (AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Loss
Total after-tax amount	$ 602,080		$ 602,080		$ 599,055
Impact on unrecognized net actuarial loss
Change in the unrecognized net actuarial loss, after tax	(98)	$ (1,931)	(1,569)	$ (5,435)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Loss
Total pre-tax amount	(29,562)		(29,562)		(31,840)
Total after-tax amount	(22,026)	(30,843)	(22,026)	(30,843)	(23,417)	$ (27,496)
Unrecognized Net Periodic Benefit Costs
Accumulated Other Comprehensive Loss
Total pre-tax amount	(27,251)		(27,251)		(29,320)
Total after-tax amount	(20,622)	(28,601)	(20,622)	(28,601)	(21,886)	(25,497)
Interest Rate Swap
Accumulated Other Comprehensive Loss
Total pre-tax amount	(186)		(186)		(542)
Total after-tax amount	(113)	(1,237)	(113)	(1,237)	(329)	(545)
Foreign Currency Translation
Accumulated Other Comprehensive Loss
Total pre-tax amount	(2,125)		(2,125)		(1,978)
Total after-tax amount	$ (1,291)	$ (1,005)	$ (1,291)	$ (1,005)	$ (1,202)	$ (1,454)