ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Reclassifications out of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Amounts Reclassified from AOCI
Interest expense	$ 5,418	$ 10,835	$ 13,370	$ 21,027
Income tax expense (benefit)	(3,129)	(2,859)	(5,805)	(6,274)
Net income	10,656	10,653	20,004	23,580
Amount Reclassified from Accumulated Other Comprehensive Income
Amounts Reclassified from AOCI
Total reclassifications, before income tax	(314)	539	(357)	966
Income tax expense (benefit)	91	(157)	104	(282)
Net income	(223)	382	(253)	684
Amount Reclassified from Accumulated Other Comprehensive Income | Realized gains (losses) on sale of available for sale securities | Net securities gains (losses)
Amounts Reclassified from AOCI
Net securities gains (losses)		201	(15)	201
Amount Reclassified from Accumulated Other Comprehensive Income | Prior service credit | Other operating expenses
Amounts Reclassified from AOCI
Other operating expenses	19	19	38	38
Amount Reclassified from Accumulated Other Comprehensive Income | Actuarial losses | Other operating expenses
Amounts Reclassified from AOCI
Other operating expenses	(157)	(147)	(314)	(295)
Amount Reclassified from Accumulated Other Comprehensive Income | Realized (losses) gains on cash flow hedges | Interest expense.
Amounts Reclassified from AOCI
Interest expense	$ (176)	$ 466	$ (66)	$ 1,022