Note 3 - Investment Securities - Amortized Cost and Fair Value of HTM and AFS Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Securities HTM:
Securities held to maturity, at amortized cost, net of allowance for credit losses	$ 683,504	$ 587,142
Securities HTM, Amortized cost	683,707	587,322
Securities HTM, Allowance for Credit (Losses)	(203)	(180)
Securities HTM, Gross Unrealized Gains	33,429	5,292
Securities HTM, Gross Unrealized (Losses)	(36,654)	(56,798)
Securities HTM, Fair Value	680,279	535,636
Securities AFS:
Securities AFS, Amortized Cost	348,633	400,511
Securities AFS, Allowance for Credit (Losses)	(989)
Securities AFS, Gross Unrealized Gains	190	160
Securities AFS, Gross Unrealized (Losses)	(48,179)	(59,711)
Securities AFS, Fair Value	299,655	340,960
U.S. treasuries and govt. sponsored agency securities
Securities AFS:
Securities AFS, Amortized Cost	17,399	19,745
Securities AFS, Gross Unrealized Gains	12	19
Securities AFS, Gross Unrealized (Losses)	(2,438)	(2,783)
Securities AFS, Fair Value	14,973	16,981
Residential mortgage-backed and related securities
Securities AFS:
Securities AFS, Amortized Cost	65,168	73,438
Securities AFS, Gross Unrealized (Losses)	(5,972)	(7,223)
Securities AFS, Fair Value	59,196	66,215
Municipal securities.
Securities HTM:
Securities HTM, Amortized cost	682,657	586,272
Securities HTM, Allowance for Credit (Losses)	(202)	(180)	$ (198)
Securities HTM, Gross Unrealized Gains	33,385	5,292
Securities HTM, Gross Unrealized (Losses)	(36,639)	(56,798)
Securities HTM, Fair Value	679,201	534,586
Securities AFS:
Securities AFS, Amortized Cost	206,566	239,812
Securities AFS, Gross Unrealized Gains	11	66
Securities AFS, Gross Unrealized (Losses)	(35,590)	(46,700)
Securities AFS, Fair Value	170,987	193,178
Asset-backed securities
Securities AFS:
Securities AFS, Amortized Cost	15,261	18,885
Securities AFS, Gross Unrealized Gains	167	48
Securities AFS, Gross Unrealized (Losses)	(5)	(205)
Securities AFS, Fair Value	15,423	18,728
Corporate Debt Securities [Member]
Securities AFS:
Securities AFS, Allowance for Credit (Losses)	(989)
Other securities
Securities HTM:
Securities HTM, Amortized cost	1,050	1,050
Securities HTM, Allowance for Credit (Losses)	(1)
Securities HTM, Gross Unrealized Gains	44
Securities HTM, Gross Unrealized (Losses)	(15)
Securities HTM, Fair Value	1,078	1,050
Securities AFS:
Securities AFS, Amortized Cost	44,239	48,631
Securities AFS, Allowance for Credit (Losses)	(989)
Securities AFS, Gross Unrealized Gains		27
Securities AFS, Gross Unrealized (Losses)	(4,174)	(2,800)
Securities AFS, Fair Value	$ 39,076	$ 45,858

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).

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