Note 7 - Investment Securities - Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Investment securities available for sale, amortized cost	$ 1,783,915	$ 1,726,080
Investment securities available for sale, gross unrealized gains	162	515
Investment securities available for sale, gross unrealized losses	130,910	122,025
Securities AFS	1,653,167	1,604,570
US Treasury Securities [Member]
Investment securities available for sale, amortized cost	541,914	495,167
Investment securities available for sale, gross unrealized gains	4	153
Investment securities available for sale, gross unrealized losses	120	20
Securities AFS	541,798	495,300
US Government Corporations and Agencies Securities [Member]
Investment securities available for sale, amortized cost	12,123	48,282
Investment securities available for sale, gross unrealized gains	61	117
Investment securities available for sale, gross unrealized losses	126	230
Securities AFS	12,058	48,169
US Government-sponsored Enterprises Debt Securities [Member]
Investment securities available for sale, amortized cost	59,785
Investment securities available for sale, gross unrealized gains	0
Investment securities available for sale, gross unrealized losses	40
Securities AFS	59,745
Collateralized Mortgage-Backed Securities [Member]
Investment securities available for sale, amortized cost	871,231	892,942
Investment securities available for sale, gross unrealized gains	63	223
Investment securities available for sale, gross unrealized losses	117,132	106,442
Securities AFS	754,162	786,723
Collateralized Mortgage Obligations [Member]
Investment securities available for sale, amortized cost	30,494	31,238
Investment securities available for sale, gross unrealized gains	0	0
Investment securities available for sale, gross unrealized losses	3,296	3,194
Securities AFS	27,198	28,044
Corporate Debt Securities [Member]
Investment securities available for sale, amortized cost	268,368	258,451
Investment securities available for sale, gross unrealized gains	34	22
Investment securities available for sale, gross unrealized losses	10,196	12,139
Securities AFS	$ 258,206	$ 246,334

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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