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INVESTMENT SECURITIES - Additional Information (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Investment Securities Pledged as Collateral |  |  |  |
Investment securities pledged to collateralize certain deposits and borrowings |  | $ 2,140,000 | $ 2,180,000 |
Gross realized losses |  | (52,329) | 0 | $ 0
Accrued interest and fees receivable |  | 5,000 | 4,700 |
Proceeds from sales of securities |  | $ 733,789 | $ 0 | $ 0
Debt Securities, Pledged Status [Extensible Enumeration] |  | us-gaap:AssetPledgedAsCollateralWithoutRightMember | us-gaap:AssetPledgedAsCollateralWithoutRightMember |
Debt Securities, Pledging Purpose [Extensible Enumeration] |  | Deposits | Deposits |
U.S. Treasury and agency securities |  |  |  |
Investment Securities Pledged as Collateral |  |  |  |
Book value of available-for-sale | $ 786,100 |  |  |
Gross realized losses | 52,300 |  |  |
Proceeds from sales of securities | $ 733,800 |  |  |
U.S. Treasury and agency securities | Securities Sold under Agreements to Repurchase |  |  |  |
Investment Securities Pledged as Collateral |  |  |  |
Investment securities pledged to collateralize certain deposits and borrowings |  | $ 598,900 | $ 466,900 |

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