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INVESTMENT SECURITIES - Available-for-Sale Portfolio (Details) - USD ($) $ in Thousands | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2022 | Dec. 31, 2021
Available-for-Sale Portfolio [Abstract] |  |
Amortized cost | $ 6,255,259 | $ 4,980,102
Gross unrealized gains | 2,793 | 65,387
Gross unrealized losses | 667,625 | 111,279
Available-for-sale investment securities | 5,590,427 | 4,934,210
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract] |  |
Amortized cost | 6,255,259 | 4,980,102
Debt Securities, Available-for-sale | 5,590,427 | 4,934,210
U.S. Treasury and Agency Securities |  |
Available-for-Sale Portfolio [Abstract] |  |
Amortized cost | 5,199,745 | 4,064,624
Available-for-sale investment securities | 4,615,546 | 3,998,564
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract] |  |
Amortized cost | 5,199,745 | 4,064,624
Gross unrealized gains | 165 | 39,997
Gross unrealized losses | 584,364 | 106,057
Debt Securities, Available-for-sale | 4,615,546 | 3,998,564
Obligations of State and Political Subdivisions |  |
Available-for-Sale Portfolio [Abstract] |  |
Amortized cost | 565,701 | 413,019
Available-for-sale investment securities | 527,155 | 430,289
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract] |  |
Amortized cost | 565,701 | 413,019
Gross unrealized gains | 2,224 | 17,326
Gross unrealized losses | 40,770 | 56
Debt Securities, Available-for-sale | 527,155 | 430,289
Government Agency Mortgage-Backed Securities |  |
Available-for-Sale Portfolio [Abstract] |  |
Amortized cost | 466,276 | 474,506
Available-for-sale investment securities | 425,357 | 477,056
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract] |  |
Amortized cost | 466,276 | 474,506
Gross unrealized gains | 397 | 7,615
Gross unrealized losses | 41,316 | 5,065
Debt Securities, Available-for-sale | 425,357 | 477,056
Corporate debt securities |  |
Available-for-Sale Portfolio [Abstract] |  |
Amortized cost | 8,000 | 8,000
Available-for-sale investment securities | 7,231 | 7,962
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract] |  |
Amortized cost | 8,000 | 8,000
Gross unrealized gains | 0 | 39
Gross unrealized losses | 769 | 77
Debt Securities, Available-for-sale | 7,231 | 7,962
Government Agency Collateralized Mortgage Obligations |  |
Available-for-Sale Portfolio [Abstract] |  |
Amortized cost | 15,537 | 19,953
Available-for-sale investment securities | 15,138 | 20,339
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract] |  |
Amortized cost | 15,537 | 19,953
Gross unrealized gains | 7 | 410
Gross unrealized losses | 406 | 24
Debt Securities, Available-for-sale | 15,138 | 20,339
Federal Reserve Bank Stock [Member] |  |
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract] |  |
Gross unrealized losses | 0 | 0
Other Equity Securities [Member] |  |
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract] |  |
Gross unrealized losses | 0 | 0
Federal Home Loan Bank Common Stock [Member] |  |
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract] |  |
Gross unrealized losses | $ 0 | $ 0

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