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Note 3 - Investment Securities - Amortized Cost, Unrealized Gains and Losses, and Estimated Fair Value of Investment Securities Portfolio (Details) - USD ($) $ in Thousands | Jun. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Debt securities available for sale, amortized cost | $ 3,392,197 | $ 3,634,471
Debt securities available for sale, gross unrealized gains | 785 | 790
Debt securities available for sale, gross unrealized losses | (166,533) | (239,451)
Debt securities available for sale | 3,226,449 | 3,395,810
Held to Maturity, Amortized Cost | 834,440 | 844,635
Held to Maturity, Gross Unrealized Gains | 1,193 | 35
Held to Maturity, Gross Unrealized Losses | (17,914) | (36,832)
Held to Maturity, Fair Value | 817,719 | 807,838
Total, amortized cost | 4,226,637 | 4,479,106
Total, gross unrealized gains | 1,978 | 825
Total, gross unrealized losses | (184,447) | (276,283)
Total, fair value | 4,044,168 | 4,203,648
Agency Residential MBS [Member] |  |
Debt securities available for sale, amortized cost | 208,198 | 229,050
Debt securities available for sale, gross unrealized gains | 1 | 1
Debt securities available for sale, gross unrealized losses | (12,921) | (17,991)
Debt securities available for sale | 195,278 | 211,060
Held to Maturity, Amortized Cost | 49,878 | 57,927
Held to Maturity, Gross Unrealized Gains | 23 | 23
Held to Maturity, Gross Unrealized Losses | (2,887) | (4,218)
Held to Maturity, Fair Value | 47,014 | 53,732
Agency Commercial MBS [Member] |  |
Debt securities available for sale, amortized cost | 95,966 | 7,098
Debt securities available for sale, gross unrealized gains | 364 | 0
Debt securities available for sale, gross unrealized losses | (65) | (132)
Debt securities available for sale | 96,265 | 6,966
US Government Agencies Debt Securities [Member] |  |
Debt securities available for sale, amortized cost | 312,417 | 311,201
Debt securities available for sale, gross unrealized gains | 27 | 1
Debt securities available for sale, gross unrealized losses | (10,541) | (19,085)
Debt securities available for sale | 301,903 | 292,117
US Treasury Securities [Member] |  |
Debt securities available for sale, amortized cost |  | 4,945
Debt securities available for sale, gross unrealized gains |  | 10
Debt securities available for sale, gross unrealized losses |  | 0
Debt securities available for sale |  | 4,955
US States and Political Subdivisions Debt Securities [Member] |  |
Debt securities available for sale, amortized cost | 61,987 | 63,878
Debt securities available for sale, gross unrealized gains | 8 | 9
Debt securities available for sale, gross unrealized losses | (1,160) | (1,701)
Debt securities available for sale | 60,835 | 62,186
Held to Maturity, Amortized Cost | 45,716 | 51,261
Held to Maturity, Gross Unrealized Gains | 8 | 12
Held to Maturity, Gross Unrealized Losses | (131) | (377)
Held to Maturity, Fair Value | 45,593 | 50,896
Corporate Debt Securities [Member] |  |
Debt securities available for sale, amortized cost | 1,931,579 | 2,031,144
Debt securities available for sale, gross unrealized gains | 0 | 127
Debt securities available for sale, gross unrealized losses | (139,558) | (195,334)
Debt securities available for sale | 1,792,021 | 1,835,937
Held to Maturity, Amortized Cost | 738,846 | 735,447
Held to Maturity, Gross Unrealized Gains | 1,162 | 0
Held to Maturity, Gross Unrealized Losses | (14,896) | (32,237)
Held to Maturity, Fair Value | 725,112 | 703,210
Collateralized Debt Obligations [Member] |  |
Debt securities available for sale, amortized cost | 782,050 | 987,155
Debt securities available for sale, gross unrealized gains | 385 | 642
Debt securities available for sale, gross unrealized losses | (2,288) | (5,208)
Debt securities available for sale | $ 780,147 | $ 982,589

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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://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-2 + Details
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- Definition Amount, before tax, of unrealized loss 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://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-2 + Details
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- Definition Amortized cost excluding accrued interest, before allowance for credit loss, of 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://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479130/326-30-45-1 + Details
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