Note 3 - Investment Securities - Securities With Unrealized Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Securities available-for-sale, less than 12 months, fair value	$ 820,786	$ 808,870
Securities available-for-sale, less than 12 months, unrealized losses	(48,314)	(12,206)
Securities available-for-sale, 12 months or more, fair value	265,088	103,568
Securities available-for-sale, 12 months or more, unrealized losses	(27,844)	(3,156)
Securities available-for-sale, fair value	1,085,874	912,438
Securities available-for-sale, unrealized losses	(76,158)	(15,362)
US Treasury Securities and US Government Agencies Debt Securities [Member]
Securities available-for-sale, less than 12 months, fair value	116,338	122,501
Securities available-for-sale, less than 12 months, unrealized losses	(5,481)	(1,252)
Securities available-for-sale, 12 months or more, fair value	0	0
Securities available-for-sale, 12 months or more, unrealized losses	0	0
Securities available-for-sale, fair value	116,338	122,501
Securities available-for-sale, unrealized losses	(5,481)	(1,252)
US Government-sponsored Enterprises Debt Securities [Member]
Securities available-for-sale, less than 12 months, fair value	94,099	23,789
Securities available-for-sale, less than 12 months, unrealized losses	(2,334)	(223)
Securities available-for-sale, 12 months or more, fair value	243	447
Securities available-for-sale, 12 months or more, unrealized losses	(7)	(13)
Securities available-for-sale, fair value	94,342	24,236
Securities available-for-sale, unrealized losses	(2,341)	(236)
Mortgage-Backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available-for-sale, less than 12 months, fair value	482,129	615,130
Securities available-for-sale, less than 12 months, unrealized losses	(33,441)	(10,027)
Securities available-for-sale, 12 months or more, fair value	263,942	102,637
Securities available-for-sale, 12 months or more, unrealized losses	(27,735)	(3,127)
Securities available-for-sale, fair value	746,071	717,767
Securities available-for-sale, unrealized losses	(61,176)	(13,154)
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale, less than 12 months, fair value	122,102	46,493
Securities available-for-sale, less than 12 months, unrealized losses	(6,923)	(686)
Securities available-for-sale, 12 months or more, fair value	903	484
Securities available-for-sale, 12 months or more, unrealized losses	(102)	(16)
Securities available-for-sale, fair value	123,005	46,977
Securities available-for-sale, unrealized losses	(7,025)	(702)
Other Debt Obligations [Member]
Securities available-for-sale, less than 12 months, fair value	6,118	957
Securities available-for-sale, less than 12 months, unrealized losses	(135)	(18)
Securities available-for-sale, 12 months or more, fair value	0	0
Securities available-for-sale, 12 months or more, unrealized losses	0	0
Securities available-for-sale, fair value	6,118	957
Securities available-for-sale, unrealized losses	$ (135)	$ (18)