Note 4 - Investment Securities - Temporarily Impaired Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Temporarily impaired securities, less than 12 months, fair value	$ 769,045	$ 639,985
Temporarily impaired securities, less than 12 months, unrealized losses	39,023	9,198
Temporarily impaired securities, 12 months or longer, fair value	562,156	28,429
Temporarily impaired securities, 12 months or longer, unrealized losses	110,492	1,435
Temporarily impaired securities, total fair value	1,331,201	668,414
Temporarily impaired securities, total unrealized losses	149,515	10,633
US Treasury Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	240,500	0
Temporarily impaired securities, less than 12 months, unrealized losses	1,111	0
Temporarily impaired securities, 12 months or longer, fair value	0	0
Temporarily impaired securities, 12 months or longer, unrealized losses	0	0
Temporarily impaired securities, total fair value	240,500	0
Temporarily impaired securities, total unrealized losses	1,111	0
US Government Corporations and Agencies Securities [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	1,806	2,337
Temporarily impaired securities, 12 months or longer, unrealized losses	121	135
Temporarily impaired securities, total fair value	1,806	2,337
Temporarily impaired securities, total unrealized losses	121	135
Collateralized Mortgage-Backed Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	394,123	527,276
Temporarily impaired securities, less than 12 months, unrealized losses	33,042	6,659
Temporarily impaired securities, 12 months or longer, fair value	452,739	6,496
Temporarily impaired securities, 12 months or longer, unrealized losses	93,941	755
Temporarily impaired securities, total fair value	846,862	533,772
Temporarily impaired securities, total unrealized losses	126,983	7,414
Collateralized Mortgage Obligations [Member]
Temporarily impaired securities, less than 12 months, fair value	24,427	8,989
Temporarily impaired securities, less than 12 months, unrealized losses	1,614	417
Temporarily impaired securities, 12 months or longer, fair value	6,634	128
Temporarily impaired securities, 12 months or longer, unrealized losses	1,877	13
Temporarily impaired securities, total fair value	31,061	9,117
Temporarily impaired securities, total unrealized losses	3,491	430
Corporate Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	109,995	103,720
Temporarily impaired securities, less than 12 months, unrealized losses	3,256	2,122
Temporarily impaired securities, 12 months or longer, fair value	100,977	19,468
Temporarily impaired securities, 12 months or longer, unrealized losses	14,553	532
Temporarily impaired securities, total fair value	210,972	123,188
Temporarily impaired securities, total unrealized losses	$ 17,809	$ 2,654

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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