STOCKHOLDERS' EQUITY (AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Loss
Total after-tax amount	$ 613,565		$ 613,565		$ 599,055
Impact on unrecognized net actuarial loss
Change in the unrecognized net actuarial loss, after tax	(1,589)	$ 1,294	(3,158)	$ (4,141)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Loss
Total pre-tax amount	(29,845)		(29,845)		(31,840)
Total after-tax amount	(22,201)	(28,439)	(22,201)	(28,439)	(23,417)	$ (27,496)
Unrecognized Net Periodic Benefit Costs
Accumulated Other Comprehensive Loss
Total pre-tax amount	(28,059)		(28,059)		(29,320)
Total after-tax amount	(21,116)	(26,039)	(21,116)	(26,039)	(21,886)	(25,497)
Interest Rate Swap
Accumulated Other Comprehensive Loss
Total pre-tax amount	(145)		(145)		(542)
Total after-tax amount	(88)	(975)	(88)	(975)	(329)	(545)
Foreign Currency Translation
Accumulated Other Comprehensive Loss
Total pre-tax amount	(1,641)		(1,641)		(1,978)
Total after-tax amount	$ (997)	$ (1,425)	$ (997)	$ (1,425)	$ (1,202)	$ (1,454)