Note 8 - Investment Securities - Temporarily Impaired Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Temporarily impaired securities, less than 12 months, fair value	$ 429,082	$ 769,045
Temporarily impaired securities, less than 12 months, unrealized losses	8,118	39,023
Temporarily impaired securities, 12 months or longer, fair value	832,385	562,156
Temporarily impaired securities, 12 months or longer, unrealized losses	124,110	110,492
Temporarily impaired securities, total fair value	1,261,467	1,331,201
Temporarily impaired securities, total unrealized losses	132,228	149,515
US Treasury Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	172,306	240,500
Temporarily impaired securities, less than 12 months, unrealized losses	501	1,111
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	172,306	240,500
Temporarily impaired securities, total unrealized losses	501	1,111
US Government Corporations and Agencies Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	6,617	0
Temporarily impaired securities, less than 12 months, unrealized losses	3	0
Temporarily impaired securities, 12 months or longer, fair value	1,676	1,806
Temporarily impaired securities, 12 months or longer, unrealized losses	124	121
Temporarily impaired securities, total fair value	8,293	1,806
Temporarily impaired securities, total unrealized losses	127	121
Collateralized Mortgage-Backed Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	127,422	394,123
Temporarily impaired securities, less than 12 months, unrealized losses	4,819	33,042
Temporarily impaired securities, 12 months or longer, fair value	709,405	452,739
Temporarily impaired securities, 12 months or longer, unrealized losses	108,246	93,941
Temporarily impaired securities, total fair value	836,827	846,862
Temporarily impaired securities, total unrealized losses	113,065	126,983
Collateralized Mortgage Obligations [Member]
Temporarily impaired securities, less than 12 months, fair value	24,326	24,427
Temporarily impaired securities, less than 12 months, unrealized losses	1,206	1,614
Temporarily impaired securities, 12 months or longer, fair value	6,641	6,634
Temporarily impaired securities, 12 months or longer, unrealized losses	1,704	1,877
Temporarily impaired securities, total fair value	30,967	31,061
Temporarily impaired securities, total unrealized losses	2,910	3,491
Corporate Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	98,411	109,995
Temporarily impaired securities, less than 12 months, unrealized losses	1,589	3,256
Temporarily impaired securities, 12 months or longer, fair value	114,663	100,977
Temporarily impaired securities, 12 months or longer, unrealized losses	14,036	14,553
Temporarily impaired securities, total fair value	213,074	210,972
Temporarily impaired securities, total unrealized losses	$ 15,625	$ 17,809