Note 4 - Investment Securities - Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Investment securities available for sale, amortized cost	$ 1,726,080	$ 1,622,173
Investment securities available for sale, gross unrealized gains	515	690
Investment securities available for sale, gross unrealized losses	122,025	149,515
Securities available-for-sale	1,604,570	1,473,348
US Treasury Securities [Member]
Investment securities available for sale, amortized cost	495,167	241,611
Investment securities available for sale, gross unrealized gains	153	0
Investment securities available for sale, gross unrealized losses	20	1,111
Securities available-for-sale	495,300	240,500
US Government Corporations and Agencies Securities [Member]
Investment securities available for sale, amortized cost	48,282	63,347
Investment securities available for sale, gross unrealized gains	117	384
Investment securities available for sale, gross unrealized losses	230	121
Securities available-for-sale	48,169	63,610
Collateralized Mortgage-Backed Securities [Member]
Investment securities available for sale, amortized cost	892,942	993,883
Investment securities available for sale, gross unrealized gains	223	194
Investment securities available for sale, gross unrealized losses	106,442	126,983
Securities available-for-sale	786,723	867,094
US Government-sponsored Enterprises Debt Securities [Member]
Investment securities available for sale, amortized cost		30,000
Investment securities available for sale, gross unrealized gains		0
Investment securities available for sale, gross unrealized losses		0
Securities available-for-sale	0	30,000
Collateralized Mortgage Obligations [Member]
Investment securities available for sale, amortized cost	31,238	34,552
Investment securities available for sale, gross unrealized gains	0	0
Investment securities available for sale, gross unrealized losses	3,194	3,491
Securities available-for-sale	28,044	31,061
Corporate Debt Securities [Member]
Investment securities available for sale, amortized cost	258,451	258,780
Investment securities available for sale, gross unrealized gains	22	112
Investment securities available for sale, gross unrealized losses	12,139	17,809
Securities available-for-sale	$ 246,334	$ 241,083

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).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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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).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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