STOCKHOLDERS' EQUITY (AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Loss
Total after-tax amount	$ 595,153		$ 595,153		$ 588,728
Impact on unrecognized net actuarial loss
Change in the unrecognized net actuarial loss, after tax	1,294	$ (6,780)	(4,141)	$ (6,232)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Loss
Total pre-tax amount	(39,915)		(39,915)		(38,507)
Total after-tax amount	(28,439)	(27,585)	(28,439)	(27,585)	(27,496)	$ (23,479)
Unrecognized Net Periodic Benefit Costs
Accumulated Other Comprehensive Loss
Total pre-tax amount	(36,118)		(36,118)		(35,231)
Total after-tax amount	(26,039)	(25,338)	(26,039)	(25,338)	(25,497)	(22,387)
Interest Rate Swap
Accumulated Other Comprehensive Loss
Total pre-tax amount	(1,605)		(1,605)		(897)
Total after-tax amount	(975)	(953)	(975)	(953)	(545)	(350)
Foreign Currency Translation
Accumulated Other Comprehensive Loss
Total pre-tax amount	(2,192)		(2,192)		(2,379)
Total after-tax amount	$ (1,425)	$ (1,294)	$ (1,425)	$ (1,294)	$ (1,454)	$ (742)