Note 3 - Investment Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Securities available-for-sale, amortized cost	$ 1,225,815	$ 1,190,379
Securities available-for-sale, unrealized gains	698	5,281
Securities available-for-sale, unrealized losses	(76,158)	(15,362)
Securities available-for-sale, fair value	1,150,355	1,180,298
US Treasury Securities and US Government Agencies Debt Securities [Member]
Securities available-for-sale, amortized cost	121,819	123,753
Securities available-for-sale, unrealized gains	0	0
Securities available-for-sale, unrealized losses	(5,481)	(1,252)
Securities available-for-sale, fair value	116,338	122,501
US Government-sponsored Enterprises Debt Securities [Member]
Securities available-for-sale, amortized cost	126,467	132,760
Securities available-for-sale, unrealized gains	525	2,497
Securities available-for-sale, unrealized losses	(2,341)	(236)
Securities available-for-sale, fair value	124,651	135,021
Mortgage-Backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available-for-sale, amortized cost	820,452	857,283
Securities available-for-sale, unrealized gains	137	2,495
Securities available-for-sale, unrealized losses	(61,176)	(13,154)
Securities available-for-sale, fair value	759,413	846,624
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale, amortized cost	150,824	75,488
Securities available-for-sale, unrealized gains	36	289
Securities available-for-sale, unrealized losses	(7,025)	(702)
Securities available-for-sale, fair value	143,835	75,075
Other Debt Obligations [Member]
Securities available-for-sale, amortized cost	6,253	1,095
Securities available-for-sale, unrealized gains	0	0
Securities available-for-sale, unrealized losses	(135)	(18)
Securities available-for-sale, fair value	$ 6,118	$ 1,077