OTHER COMPREHENSIVE INCOME (LOSS) (reclassification adjustments) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification adjustments [Line Items]
Interest expense									$ (34,682)	$ (27,112)	$ (21,359)
Income tax provision									(14,267)	(63,001)	(82,672)
Net (loss) income	$ 44,824	$ (318,493)	$ 32,582	$ 41,190	$ 57,170	$ (31,083)	$ 60,207	$ 63,336	(199,897)	149,630	230,155
Other income									7,193	8,522	5,010
Amounts reclassified from accumulated other comprehensive loss [Member]
Reclassification adjustments [Line Items]
Net (loss) income									(1,472)	(972)	(1,844)
Prior service credit [Member] | Amounts reclassified from accumulated other comprehensive loss [Member]
Reclassification adjustments [Line Items]
Other income									1,421	1,421	1,421
Net actuarial loss [Member] | Amounts reclassified from accumulated other comprehensive loss [Member]
Reclassification adjustments [Line Items]
Other income									(3,223)	(2,884)	(3,637)
Total amortization [Member] | Amounts reclassified from accumulated other comprehensive loss [Member]
Reclassification adjustments [Line Items]
Income tax provision									273	491	372
Net (loss) income									(1,529)	(972)	(1,844)
Other income									(1,802)	(1,463)	(2,216)
Realized gains on interest rate swap [Member] | Amounts reclassified from accumulated other comprehensive loss [Member]
Reclassification adjustments [Line Items]
Interest expense									77	0	0
Income tax provision									(20)	0	0
Net (loss) income									$ 57	$ 0	$ 0