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INVESTMENT SECURITIES - Available-for-sale portfolio (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021
Available-for-Sale Portfolio |  |
Amortized cost | $ 4,675,474 | $ 4,980,102
Gross unrealized gains | 565 | 65,387
Gross unrealized losses | 524,188 | 111,279
Total - Fair value | 4,151,851 | 4,934,210
Debt Securities, Available-for-sale, Fair Value to Amortized Cost |  |
Amortized cost | 4,675,474 | 4,980,102
Total - Fair value | 4,151,851 | 4,934,210
U.S. Treasury and agency securities |  |
Available-for-Sale Portfolio |  |
Amortized cost | 3,660,546 | 4,064,624
Total - Fair value | 3,243,537 | 3,998,564
Debt Securities, Available-for-sale, Fair Value to Amortized Cost |  |
Amortized cost | 3,660,546 | 4,064,624
Gross unrealized gains | 0 | 39,997
Gross unrealized losses | 417,009 | 106,057
Total - Fair value | 3,243,537 | 3,998,564
Obligations of state and political subdivisions |  |
Available-for-Sale Portfolio |  |
Amortized cost | 549,118 | 413,019
Total - Fair value | 504,297 | 430,289
Debt Securities, Available-for-sale, Fair Value to Amortized Cost |  |
Amortized cost | 549,118 | 413,019
Gross unrealized gains | 506 | 17,326
Gross unrealized losses | 45,327 | 56
Total - Fair value | 504,297 | 430,289
Government agency mortgage-backed securities |  |
Available-for-Sale Portfolio |  |
Amortized cost | 444,689 | 474,506
Total - Fair value | 384,633 | 477,056
Debt Securities, Available-for-sale, Fair Value to Amortized Cost |  |
Amortized cost | 444,689 | 474,506
Gross unrealized gains | 58 | 7,615
Gross unrealized losses | 60,114 | 5,065
Total - Fair value | 384,633 | 477,056
Corporate debt securities |  |
Available-for-Sale Portfolio |  |
Amortized cost | 8,000 | 8,000
Total - Fair value | 7,114 | 7,962
Debt Securities, Available-for-sale, Fair Value to Amortized Cost |  |
Amortized cost | 8,000 | 8,000
Gross unrealized gains | 0 | 39
Gross unrealized losses | 886 | 77
Total - Fair value | 7,114 | 7,962
Government agency collateralized mortgage obligations |  |
Available-for-Sale Portfolio |  |
Amortized cost | 13,121 | 19,953
Total - Fair value | 12,270 | 20,339
Debt Securities, Available-for-sale, Fair Value to Amortized Cost |  |
Amortized cost | 13,121 | 19,953
Gross unrealized gains | 1 | 410
Gross unrealized losses | 852 | 24
Total - Fair value | 12,270 | 20,339
Federal reserve bank common stock |  |
Debt Securities, Available-for-sale, Fair Value to Amortized Cost |  |
Gross unrealized losses | 0 | 0
Other equity securities |  |
Debt Securities, Available-for-sale, Fair Value to Amortized Cost |  |
Gross unrealized losses | 0 | 0
Federal home loan bank common stock |  |
Debt Securities, Available-for-sale, Fair Value to Amortized Cost |  |
Gross unrealized losses | $ 0 | $ 0

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- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563 + Details
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