ACCUMULATED OTHER COMPREHENSIVE INCOME- Summary of reclassification out of each component of accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Unrealized (loss) gain on securities available for sale: Realized (losses) gains on securities available for sale		$ (1)	$ 69
Interest (expense) income		42,949	39,068
Compensation and employee benefits		25,206	22,639
Income tax expense		(9,618)	7,866
Total reclassification for the period, net of tax	$ (36,342)	(36,342)	(31,506)
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense		479	247
Total reclassification for the period, net of tax		(1,159)	(625)
Unrealized (loss) gain on securities available for sale: Realized (losses) gains on securities available for sale | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Unrealized (loss) gain on securities available for sale: Realized (losses) gains on securities available for sale		(1)	69
Gains and (losses) on cash flow hedges: | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest (expense) income		(1,427)	(752)
Defined Benefit Pension Items | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Compensation and employee benefits		$ (210)	$ (189)