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FAIR VALUE - Financial assets and liabilities accounted for at fair value on a recurring basis (Details) - USD ($) $ in Thousands | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Available-for-sale investment securities |  |
Fair Value | $ 2,919,992 | $ 4,151,851
Equity securities | 372 | 419
Mortgage loans held for sale |  | 0
Unpaid principal value of mortgage loans held for sale | 400 |
Fair value, assets, levels transfers | 0 |
U.S. Treasury and agency securities |  |
Available-for-sale investment securities |  |
Fair Value | 2,080,783 | 3,243,537
Obligations of state and political subdivisions |  |
Available-for-sale investment securities |  |
Fair Value | 474,363 | 504,297
Government agency mortgage-backed securities |  |
Available-for-sale investment securities |  |
Fair Value | 348,526 | 384,633
Corporate debt securities |  |
Available-for-sale investment securities |  |
Fair Value | 7,394 | 7,114
Government agency collateralized mortgage obligations |  |
Available-for-sale investment securities |  |
Fair Value | 8,926 | 12,270
Level 3 | Commitments to originate real estate loans for sale |  |
Available-for-sale investment securities |  |
Derivative asset | 2 | 5
Recurring |  |
Available-for-sale investment securities |  |
Fair Value | 2,919,992 | 4,151,851
Equity securities | 372 | 419
Mortgage loans held for sale | 414 |
Total | 2,920,786 | 4,152,280
Recurring | Interest rate swap agreements |  |
Available-for-sale investment securities |  |
Derivative asset |  | 1
Derivative liability |  | (1)
Recurring | Forward sales commitments |  |
Available-for-sale investment securities |  |
Derivative asset | 6 | 5
Recurring | Commitments to originate real estate loans for sale |  |
Available-for-sale investment securities |  |
Derivative asset | 2 | 5
Recurring | U.S. Treasury and agency securities |  |
Available-for-sale investment securities |  |
Fair Value | 2,080,783 | 3,243,537
Recurring | Obligations of state and political subdivisions |  |
Available-for-sale investment securities |  |
Fair Value | 474,363 | 504,297
Recurring | Government agency mortgage-backed securities |  |
Available-for-sale investment securities |  |
Fair Value | 348,526 | 384,633
Recurring | Corporate debt securities |  |
Available-for-sale investment securities |  |
Fair Value | 7,394 | 7,114
Recurring | Government agency collateralized mortgage obligations |  |
Available-for-sale investment securities |  |
Fair Value | 8,926 | 12,270
Recurring | Level 1 |  |
Available-for-sale investment securities |  |
Fair Value | 2,019,089 | 3,178,189
Equity securities | 372 | 419
Mortgage loans held for sale | 0 |
Total | 2,019,461 | 3,178,608
Recurring | Level 1 | Interest rate swap agreements |  |
Available-for-sale investment securities |  |
Derivative asset |  | 0
Derivative liability |  | 0
Recurring | Level 1 | Forward sales commitments |  |
Available-for-sale investment securities |  |
Derivative asset | 0 | 0
Recurring | Level 1 | Commitments to originate real estate loans for sale |  |
Available-for-sale investment securities |  |
Derivative asset | 0 | 0
Recurring | Level 1 | U.S. Treasury and agency securities |  |
Available-for-sale investment securities |  |
Fair Value | 2,019,089 | 3,178,189
Recurring | Level 1 | Obligations of state and political subdivisions |  |
Available-for-sale investment securities |  |
Fair Value | 0 | 0
Recurring | Level 1 | Government agency mortgage-backed securities |  |
Available-for-sale investment securities |  |
Fair Value | 0 | 0
Recurring | Level 1 | Corporate debt securities |  |
Available-for-sale investment securities |  |
Fair Value | 0 | 0
Recurring | Level 1 | Government agency collateralized mortgage obligations |  |
Available-for-sale investment securities |  |
Fair Value | 0 | 0
Recurring | Level 2 |  |
Available-for-sale investment securities |  |
Fair Value | 900,903 | 973,662
Equity securities | 0 | 0
Mortgage loans held for sale | 414 |
Total | 901,323 | 973,667
Recurring | Level 2 | Interest rate swap agreements |  |
Available-for-sale investment securities |  |
Derivative asset |  | 1
Derivative liability |  | (1)
Recurring | Level 2 | Forward sales commitments |  |
Available-for-sale investment securities |  |
Derivative asset | 6 | 5
Recurring | Level 2 | Commitments to originate real estate loans for sale |  |
Available-for-sale investment securities |  |
Derivative asset | 0 | 0
Recurring | Level 2 | U.S. Treasury and agency securities |  |
Available-for-sale investment securities |  |
Fair Value | 61,694 | 65,348
Recurring | Level 2 | Obligations of state and political subdivisions |  |
Available-for-sale investment securities |  |
Fair Value | 474,363 | 504,297
Recurring | Level 2 | Government agency mortgage-backed securities |  |
Available-for-sale investment securities |  |
Fair Value | 348,526 | 384,633
Recurring | Level 2 | Corporate debt securities |  |
Available-for-sale investment securities |  |
Fair Value | 7,394 | 7,114
Recurring | Level 2 | Government agency collateralized mortgage obligations |  |
Available-for-sale investment securities |  |
Fair Value | 8,926 | 12,270
Recurring | Level 3 |  |
Available-for-sale investment securities |  |
Fair Value | 0 | 0
Equity securities | 0 | 0
Mortgage loans held for sale | 0 |
Total | 2 | 5
Recurring | Level 3 | Interest rate swap agreements |  |
Available-for-sale investment securities |  |
Derivative asset |  | 0
Derivative liability |  | 0
Recurring | Level 3 | Forward sales commitments |  |
Available-for-sale investment securities |  |
Derivative asset | 0 | 0
Recurring | Level 3 | Commitments to originate real estate loans for sale |  |
Available-for-sale investment securities |  |
Derivative asset | 2 | 5
Recurring | Level 3 | U.S. Treasury and agency securities |  |
Available-for-sale investment securities |  |
Fair Value | 0 | 0
Recurring | Level 3 | Obligations of state and political subdivisions |  |
Available-for-sale investment securities |  |
Fair Value | 0 | 0
Recurring | Level 3 | Government agency mortgage-backed securities |  |
Available-for-sale investment securities |  |
Fair Value | 0 | 0
Recurring | Level 3 | Corporate debt securities |  |
Available-for-sale investment securities |  |
Fair Value | 0 | 0
Recurring | Level 3 | Government agency collateralized mortgage obligations |  |
Available-for-sale investment securities |  |
Fair Value | $ 0 | $ 0

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