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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	Mar. 31, 2025	Dec. 31, 2024
Debt securities available for sale, amortized cost	$ 3,430,221	$ 3,634,471
Debt securities available for sale, gross unrealized gains	995	790
Debt securities available for sale, gross unrealized losses	(195,167)	(239,451)
Debt securities available for sale	3,236,049	3,395,810
Held to Maturity, Amortized Cost	839,349	844,635
Held to Maturity, Gross Unrealized Gains	312	35
Held to Maturity, Gross Unrealized Losses	(26,536)	(36,832)
Held to Maturity, Fair Value	813,125	807,838
Total	4,269,570	4,479,106
Total	1,307	825
Total	(221,703)	(276,283)
Total	4,049,174	4,203,648
Agency Residential MBS [Member]
Debt securities available for sale, amortized cost	218,825	229,050
Debt securities available for sale, gross unrealized gains	4	1
Debt securities available for sale, gross unrealized losses	(14,487)	(17,991)
Debt securities available for sale	204,342	211,060
Held to Maturity, Amortized Cost	53,528	57,927
Held to Maturity, Gross Unrealized Gains	23	23
Held to Maturity, Gross Unrealized Losses	(3,418)	(4,218)
Held to Maturity, Fair Value	50,133	53,732
Agency Commercial MBS [Member]
Debt securities available for sale, amortized cost	46,057	7,098
Debt securities available for sale, gross unrealized gains	451	0
Debt securities available for sale, gross unrealized losses	(6)	(132)
Debt securities available for sale	46,502	6,966
US Government Agencies Debt Securities [Member]
Debt securities available for sale, amortized cost	311,809	311,201
Debt securities available for sale, gross unrealized gains	19	1
Debt securities available for sale, gross unrealized losses	(12,106)	(19,085)
Debt securities available for sale	299,722	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	62,177	63,878
Debt securities available for sale, gross unrealized gains	7	9
Debt securities available for sale, gross unrealized losses	(1,603)	(1,701)
Debt securities available for sale	60,581	62,186
Held to Maturity, Amortized Cost	48,675	51,261
Held to Maturity, Gross Unrealized Gains	12	12
Held to Maturity, Gross Unrealized Losses	(203)	(377)
Held to Maturity, Fair Value	48,484	50,896
Corporate Debt Securities [Member]
Debt securities available for sale, amortized cost	1,967,432	2,031,144
Debt securities available for sale, gross unrealized gains	0	127
Debt securities available for sale, gross unrealized losses	(164,641)	(195,334)
Debt securities available for sale	1,802,791	1,835,937
Held to Maturity, Amortized Cost	737,146	735,447
Held to Maturity, Gross Unrealized Gains	277	0
Held to Maturity, Gross Unrealized Losses	(22,915)	(32,237)
Held to Maturity, Fair Value	714,508	703,210
Collateralized Debt Obligations [Member]
Debt securities available for sale, amortized cost	823,921	987,155
Debt securities available for sale, gross unrealized gains	514	642
Debt securities available for sale, gross unrealized losses	(2,324)	(5,208)
Debt securities available for sale	$ 822,111	$ 982,589

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