ACCUMULATED OTHER COMPREHENSIVE INCOME- Summary of reclassification out of each component of accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest (expense) income	$ 11,104			$ 9,629			$ 30,613	$ 29,748
Compensation and employee benefits	5,931			6,125			18,321	17,694
Income tax expense	6,217			1,098			6,485	6,489
Total reclassification for the period, net of tax	14,970	$ 1,003	$ 745	1,665	$ 16,744	$ 11,334	16,718	29,744
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense	118			103			341	61
Total reclassification for the period, net of tax	302			263			873	157
Interest rate contracts | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest (expense) income	(368)			(317)			(1,059)	(413)
Net actuarial loss | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Compensation and employee benefits	$ (52)			$ (49)			$ (155)	$ 195