STOCKHOLDERS' EQUITY (AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Loss
Total after-tax amount	$ 577,251		$ 588,728
Impact on unrecognized net actuarial loss
Change in the unrecognized net actuarial loss, after tax	(3,504)	$ (1,831)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Loss
Total pre-tax amount	(42,163)		(38,507)
Total after-tax amount	(29,727)	(24,658)	(27,496)	$ (23,479)
Unrecognized Net Periodic Benefit Costs
Accumulated Other Comprehensive Loss
Total pre-tax amount	(38,943)		(35,231)
Total after-tax amount	(27,766)	(22,907)	(25,497)	(22,387)
Interest Rate Swap
Accumulated Other Comprehensive Loss
Total pre-tax amount	(1,796)		(897)
Total after-tax amount	(1,091)	(714)	(545)	(350)
Foreign Currency Translation
Accumulated Other Comprehensive Loss
Total pre-tax amount	(1,424)		(2,379)
Total after-tax amount	$ (870)	$ (1,037)	$ (1,454)	$ (742)