Note 7 - Investment Securities - Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Investment securities available for sale, amortized cost	$ 1,073,074	$ 1,019,230
Investment securities available for sale, gross unrealized gains	14,264	18,779
Investment securities available for sale, gross unrealized losses	8,122	1,459
Securities available-for-sale	1,079,216	1,036,550
US Treasury Securities [Member]
Investment securities available for sale, amortized cost	40,206	80,948
Investment securities available for sale, gross unrealized gains	5	6
Investment securities available for sale, gross unrealized losses	0	6
Securities available-for-sale	40,211	80,948
US Government Corporations and Agencies Securities [Member]
Investment securities available for sale, amortized cost	89,823	99,944
Investment securities available for sale, gross unrealized gains	1,255	441
Investment securities available for sale, gross unrealized losses	135	546
Securities available-for-sale	90,943	99,839
Collateralized Mortgage Backed Securities [Member]
Investment securities available for sale, amortized cost	798,905	709,709
Investment securities available for sale, gross unrealized gains	12,490	17,965
Investment securities available for sale, gross unrealized losses	6,328	606
Securities available-for-sale	805,067	727,068
Collateralized Mortgage Obligations [Member]
Investment securities available for sale, amortized cost	9,792	10,358
Investment securities available for sale, gross unrealized gains	0	0
Investment securities available for sale, gross unrealized losses	231	34
Securities available-for-sale	9,561	10,324
Corporate Debt Securities [Member]
Investment securities available for sale, amortized cost	134,348	118,271
Investment securities available for sale, gross unrealized gains	514	367
Investment securities available for sale, gross unrealized losses	1,428	267
Securities available-for-sale	$ 133,434	$ 118,371