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LOANS AND ALLOWANCE FOR LOAN AND LEASE LOSSES (Narrative) (Details) | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2024 USD ($) segment loan | Mar. 31, 2023 USD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Nonaccrual loans, interest income | $ 0 |  | $ 0 |
Loans under modified terms |  | $ 20,541,000 |  |
Total Allowance for credit losses | 136,190,000 | 116,512,000 | 132,182,000 | $ 110,768,000
Transfer from LHFI to LHFS | $ 0 | 7,087,000 |  |
Number of operating segments | segment | 2 |  |  |
Loans held for investment, accrued interest receivable | $ 72,800,000 |  | $ 72,500,000 |
Financing Receivable Accrued Interest After Allowance For Credit Loss Statement Of Financial Position Extensible List Not Disclosed (Flag) | true |  | true |
Commercial Portfolio |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Total Allowance for credit losses | $ 110,528,000 | 88,086,000 | $ 105,896,000 | $ 82,753,000
Troubled Loan Modifications |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Unfunded commitments on TLM loans | 1,100,000 | 4,400,000 |  |
TLM loans that went into default | $ 1,000,000.0 |  |  |
Troubled Loan Modifications | Past Due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Number of loans designated as TLMS currently past due | loan | 3 |  |  |
TLMs that are past due | $ 3,400,000 | $ 0 |  |

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