ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Reclassifications out of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassifications out of accumulated other comprehensive (loss) income
Interest expense	$ 5,589	$ 9,639	$ 18,959	$ 30,666
Loss on termination of swaps	(3,403)		(3,403)
Income tax benefit	(3,999)	(3,852)	(9,804)	(10,126)
Net income	13,061	13,903	33,065	37,483
Reclassifications out of accumulated other comprehensive (loss) income
Reclassifications out of accumulated other comprehensive (loss) income
Total reclassifications, before income tax	(936)	203	(1,293)	1,169
Income tax benefit	274	(59)	378	(341)
Net income	(662)	144	(915)	828
Reclassifications out of accumulated other comprehensive (loss) income | Realized gains on sale of available for sale securities | Net securities gains (losses)
Reclassifications out of accumulated other comprehensive (loss) income
Net securities gains	3,540		3,525	201
Reclassifications out of accumulated other comprehensive (loss) income | Prior service credit | Other operating expenses
Reclassifications out of accumulated other comprehensive (loss) income
Other operating expenses	20	20	58	58
Reclassifications out of accumulated other comprehensive (loss) income | Actuarial losses | Other operating expenses
Reclassifications out of accumulated other comprehensive (loss) income
Other operating expenses	(156)	(148)	(470)	(443)
Reclassifications out of accumulated other comprehensive (loss) income | Realized (losses) gains on cash flow hedges | Interest expense.
Reclassifications out of accumulated other comprehensive (loss) income
Interest expense	(992)	$ 331	(1,058)	$ 1,353
Reclassifications out of accumulated other comprehensive (loss) income | Realized (losses) gains on cash flow hedges | Loss on termination of swaps
Reclassifications out of accumulated other comprehensive (loss) income
Loss on termination of swaps	$ (3,348)		$ (3,348)