ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Reclassifications out of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Amounts Reclassified from AOCI
Interest expense	$ 10,192	$ 6,825
Income tax (expense) benefit	3,415	3,181
Net income	12,927	12,073
Amount Reclassified from Accumulated Other Comprehensive Income
Amounts Reclassified from AOCI
Total reclassifications, before income tax	427	(160)
Income tax (expense) benefit	(125)	47
Net income	302	(113)
Amount Reclassified from Accumulated Other Comprehensive Income | Prior service credit
Amounts Reclassified from AOCI
Other operating expenses	19	19
Amount Reclassified from Accumulated Other Comprehensive Income | Transition obligation
Amounts Reclassified from AOCI
Other operating expenses		(1)
Amount Reclassified from Accumulated Other Comprehensive Income | Actuarial losses
Amounts Reclassified from AOCI
Other operating expenses	(148)	(113)
Amount Reclassified from Accumulated Other Comprehensive Income | Realized gains (losses) on cash flow hedges
Amounts Reclassified from AOCI
Interest expense	$ 556	$ (65)