FAIR VALUE OF FINANCIAL INSTRUMENTS - Fair value option and gains and losses from fair value changes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Fair Value, Option, Quantitative Disclosures [Line Items]
Aggregate fair value	$ 26,621		$ 26,621		$ 138,090
Difference	499		499		810
Contractual principal	26,122		26,122		137,280
Gains and losses from fair value changes
Gains and losses from fair value changes of loan held for sales	(231)	$ (270)	(361)	$ 517
Commercial Loan Portfolio
Fair Value, Option, Quantitative Disclosures [Line Items]
Aggregate fair value	17,013		17,013		126,123
Difference	0		0		67
Contractual principal	17,013		17,013		126,056
Gains and losses from fair value changes
Gains and losses from fair value changes of loan held for sales	0	(156)	(67)	(38)
Residential Portfolio Segment
Fair Value, Option, Quantitative Disclosures [Line Items]
Aggregate fair value	9,608		9,608		11,967
Difference	499		499		743
Contractual principal	9,109		9,109		$ 11,224
Gains and losses from fair value changes
Gains and losses from fair value changes of loan held for sales	$ (231)	$ (114)	$ (294)	$ 555