Note 7 - Investment Securities - Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Investment securities available for sale, amortized cost	$ 991,724	$ 1,019,230
Investment securities available for sale, gross unrealized gains	15,637	18,779
Investment securities available for sale, gross unrealized losses	4,846	1,459
Investment securities available for sale, Estimated fair value	1,002,515	1,036,550
US Treasury Securities [Member]
Investment securities available for sale, amortized cost	40,458	80,948
Investment securities available for sale, gross unrealized gains	9	6
Investment securities available for sale, gross unrealized losses	0	6
Investment securities available for sale, Estimated fair value	40,467	80,948
US Government Corporations and Agencies Securities [Member]
Investment securities available for sale, amortized cost	92,120	99,944
Investment securities available for sale, gross unrealized gains	1,329	441
Investment securities available for sale, gross unrealized losses	137	546
Investment securities available for sale, Estimated fair value	93,312	99,839
Collateralized Mortgage Backed Securities [Member]
Investment securities available for sale, amortized cost	739,672	709,709
Investment securities available for sale, gross unrealized gains	13,640	17,965
Investment securities available for sale, gross unrealized losses	3,836	606
Investment securities available for sale, Estimated fair value	749,476	727,068
Collateralized Mortgage Obligations [Member]
Investment securities available for sale, amortized cost	10,010	10,358
Investment securities available for sale, gross unrealized gains	0	0
Investment securities available for sale, gross unrealized losses	274	34
Investment securities available for sale, Estimated fair value	9,736	10,324
Corporate Debt Securities [Member]
Investment securities available for sale, amortized cost	109,464	118,271
Investment securities available for sale, gross unrealized gains	659	367
Investment securities available for sale, gross unrealized losses	599	267
Investment securities available for sale, Estimated fair value	$ 109,524	$ 118,371

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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