OTHER COMPREHENSIVE INCOME (Changes in Accumulated Other Comprehensive Income, Net of Tax) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AOCI, Beginning balance	$ (120,069)	$ (161,714)	$ (99,631)
Other comprehensive income (loss) before reclassifications	(20,583)	23,832	(69,051)
Amounts reclassified from AOCI	1,276	17,813	6,968
Other comprehensive income (loss)	(19,307)	41,645	(62,083)
AOCI, Ending balance	(139,376)	(120,069)	(161,714)
Reclassification Adjustment for Cash Flow Hedge Losses [Member]
AOCI, Beginning balance	(14,494)	(20,322)	(25,178)
Other comprehensive income (loss) before reclassifications	0	0	0
Amounts reclassified from AOCI	1,194	5,828	4,856
Other comprehensive income (loss)	1,194	5,828	4,856
AOCI, Ending balance	(13,300)	(14,494)	(20,322)
Amortization of Pension and Postretirement Plan Actuarial Loss and Prior Service Cost [Member]
AOCI, Beginning balance	(105,575)	(141,392)	(74,453)
Other comprehensive income (loss) before reclassifications	(20,583)	23,832	(69,051)
Amounts reclassified from AOCI	82	11,985	2,112
Other comprehensive income (loss)	(20,501)	35,817	(66,939)
AOCI, Ending balance	$ (126,076)	$ (105,575)	$ (141,392)