FAIR VALUE - Summary of carrying amounts and estimated fair values for financial instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
Assets:
Cash and cash equivalents	$ 245,799	$ 254,442	$ 297,568	$ 196,512
Held-to-maturity securities, net of ACL	71,067	66,617
Total	2,456,063	2,530,915
Accrued interest receivable	11,339	11,428
Liabilities:
FHLB borrowings – fixed rate	191,505	125,711
Subordinated notes	52,451	52,340
Accrued interest payable	2,243	3,793
Carrying Amount
Assets:
Cash and cash equivalents	245,799	254,442
Held-to-maturity securities, net of ACL	78,927	74,102
Total	2,418,554	2,493,258
Accrued interest receivable	11,339	11,428
Liabilities:
Term deposits	519,597	496,452
Non-term deposits	1,891,295	2,032,587
FHLB borrowings – fixed rate	128,712	41,175
FHLB borrowings – floating rate	50,000	50,000
Federal Reserve borrowings – fixed rate	12,793	34,536
Accrued interest payable	2,243	3,793
Subordinated Notes | Carrying Amount
Liabilities:
Subordinated notes	52,451	52,340
Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimate of Fair Value Measurement
Assets:
Cash and cash equivalents	245,799	254,442
Held-to-maturity securities, net of ACL	248	242
Accrued interest receivable	11,339	11,428
Liabilities:
Term deposits	463,850	414,613
Non-term deposits	1,891,295	2,032,587
Federal Reserve borrowings – fixed rate	2,793	3,539
Accrued interest payable	2,243	3,793
Significant Other Observable Inputs (Level 2) | Estimate of Fair Value Measurement
Assets:
Held-to-maturity securities, net of ACL	62,850	58,231
Liabilities:
FHLB borrowings – fixed rate	128,752	41,372
FHLB borrowings – floating rate	49,054	49,986
Federal Reserve borrowings – fixed rate	9,947	30,936
Significant Unobservable Inputs (Level 3) | Estimate of Fair Value Measurement
Assets:
Held-to-maturity securities, net of ACL	7,969	8,144
Total	2,323,908	2,395,468
Liabilities:
Term deposits	55,425	82,564
Significant Unobservable Inputs (Level 3) | Subordinated Notes | Estimate of Fair Value Measurement
Liabilities:
Subordinated notes	$ 46,621	$ 48,228