Note 7 - Investment Securities - Temporarily Impaired Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Temporarily impaired securities, less than 12 months, fair value	$ 610,955	$ 59,054
Temporarily impaired securities, less than 12 months, unrealized losses	586	1,067
Temporarily impaired securities, 12 months or longer, fair value	775,267	807,644
Temporarily impaired securities, 12 months or longer, unrealized losses	97,933	120,978
Temporarily impaired securities, total fair value	1,386,222	866,698
Temporarily impaired securities, total unrealized losses	98,519	122,045
Temporarily impaired securities, 12 months or longer, fair value	775,267	807,644
US Treasury Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	570,370
Temporarily impaired securities, less than 12 months, unrealized losses	140
Temporarily impaired securities, 12 months or longer, fair value	0
Temporarily impaired securities, 12 months or longer, unrealized losses	0
Temporarily impaired securities, total fair value	570,370
Temporarily impaired securities, total unrealized losses	140
Temporarily impaired securities, 12 months or longer, fair value	0
US Government Corporations and Agencies Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	2,332	4,199
Temporarily impaired securities, less than 12 months, unrealized losses	2	8
Temporarily impaired securities, 12 months or longer, fair value	2,845	2,108
Temporarily impaired securities, 12 months or longer, unrealized losses	109	119
Temporarily impaired securities, total fair value	5,177	6,307
Temporarily impaired securities, total unrealized losses	111	127
Temporarily impaired securities, 12 months or longer, fair value	2,845	2,108
Collateralized Mortgage-Backed Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	28,273	29,955
Temporarily impaired securities, less than 12 months, unrealized losses	424	959
Temporarily impaired securities, 12 months or longer, fair value	628,662	653,236
Temporarily impaired securities, 12 months or longer, unrealized losses	92,407	112,237
Temporarily impaired securities, total fair value	656,935	683,191
Temporarily impaired securities, total unrealized losses	92,831	113,196
Temporarily impaired securities, 12 months or longer, fair value	628,662	653,236
Collateralized Mortgage Obligations [Member]
Temporarily impaired securities, less than 12 months, fair value	0	0
Temporarily impaired securities, less than 12 months, unrealized losses	0	0
Temporarily impaired securities, 12 months or longer, fair value	23,927	24,556
Temporarily impaired securities, 12 months or longer, unrealized losses	2,096	3,191
Temporarily impaired securities, total fair value	23,927	24,556
Temporarily impaired securities, total unrealized losses	2,096	3,191
Temporarily impaired securities, 12 months or longer, fair value	23,927	24,556
Corporate Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	9,980	24,900
Temporarily impaired securities, less than 12 months, unrealized losses	20	100
Temporarily impaired securities, 12 months or longer, fair value	119,833	127,744
Temporarily impaired securities, 12 months or longer, unrealized losses	3,321	5,431
Temporarily impaired securities, total fair value	129,813	152,644
Temporarily impaired securities, total unrealized losses	3,341	5,531
Temporarily impaired securities, 12 months or longer, fair value	$ 119,833	$ 127,744

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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