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LOANS AND ALLOWANCE FOR LOAN AND LEASE LOSSES (Narrative) (Details) | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2025 USD ($) | Sep. 30, 2024 USD ($) | Sep. 30, 2025 USD ($) segment | Sep. 30, 2024 USD ($) | Dec. 31, 2024 USD ($) segment | Jun. 30, 2025 USD ($) | Jun. 26, 2025 USD ($) | Apr. 01, 2025 USD ($) | Jun. 30, 2024 USD ($) | Dec. 31, 2023 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |
Gain on CRE loan sale |  |  | $ 10,915,000 | $ 0 |  |  |  |  |  |
Nonaccrual loans, interest income | $ 0 | $ 0 | 0 | 0 |  |  |  |  |  |
Loans under modified terms | 2,183,000 | 1,296,000 | 16,148,000 | 24,477,000 |  |  |  |  |  |
Amortized Cost | 2,183,000 | 1,296,000 | 16,148,000 | 24,477,000 |  |  |  |  |  |
Total Allowance for credit losses | 293,035,000 | 160,685,000 | 293,035,000 | 160,685,000 | $ 178,644,000 | $ 315,574,000 |  |  | $ 158,131,000 | $ 132,182,000
Unfunded commitments on loans modified and designated as TLMs | 0 |  | 0 |  | $ 0 |  |  |  |  |
TLM loans that went into default | 0 | 0 | 0 | 0 |  |  |  |  |  |
TLMs that are past due | 0 | 0 | $ 0 | 0 |  |  |  |  |  |
Number of reportable segments | segment |  |  | 2 |  | 2 |  |  |  |  |
Loans held for investment, accrued interest receivable | 103,600,000 |  | $ 103,600,000 |  | $ 73,700,000 |  |  |  |  |
Financing Receivable Accrued Interest After Allowance For Credit Loss Statement Of Financial Position Extensible List Not Disclosed (Flag) |  |  | true |  | true |  |  |  |  |
Revolving loans converted to term |  |  | $ 0 |  | $ 0 |  |  |  |  |
Sandy Spring |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |
Unpaid principle balance of CRE loans acquired |  |  |  |  |  |  | $ 2,000,000,000 |  |  |
Commercial Portfolio Segment [Member] |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |
Total Allowance for credit losses | 233,759,000 | $ 132,720,000 | 233,759,000 | $ 132,720,000 | $ 148,887,000 | $ 257,403,000 |  |  | $ 131,139,000 | $ 105,896,000
CRE | Sandy Spring |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |
LHFS |  |  |  |  |  |  |  | $ 1,839,638,000 |  |
Gain on CRE loan sale |  |  | 10,900,000 |  |  |  |  |  |  |
Commercial Real Estate | Sandy Spring |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |
Gain on CRE loan sale | $ (4,800,000) |  | $ 10,900,000 |  |  |  |  |  |  |

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