Note 4 - Investment Securities - Continuous Unrealized Loss Position (Details) $ in Thousands	Jun. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
Unrealized loss position, fair value, less than 12 months	$ 388	$ 781
Unrealized loss position, unrealized losses, less than 12 months	(8)	(22)
Unrealized loss position, fair value, more than 12 months	520,746	539,288
Unrealized loss position, unrealized losses, more than 12 months	(84,361)	(76,470)
Unrealized loss position, fair value	521,134	540,069
Unrealized loss position, unrealized losses	$ (84,369)	$ (76,492)
Number of securities, less than 12 months	1	2
Number of securities, more than 12 months	416	414
Number of securities	417	416
US Government Agencies Debt Securities [Member]
Unrealized loss position, fair value, less than 12 months	$ 0	$ 0
Unrealized loss position, unrealized losses, less than 12 months	0	0
Unrealized loss position, fair value, more than 12 months	100,846	101,366
Unrealized loss position, unrealized losses, more than 12 months	(12,307)	(11,194)
Unrealized loss position, fair value	100,846	101,366
Unrealized loss position, unrealized losses	$ (12,307)	(11,194)
Number of securities	46
US States and Political Subdivisions Debt Securities [Member]
Unrealized loss position, fair value, less than 12 months	$ 388	781
Unrealized loss position, unrealized losses, less than 12 months	(8)	(22)
Unrealized loss position, fair value, more than 12 months	239,650	244,224
Unrealized loss position, unrealized losses, more than 12 months	(38,537)	(33,814)
Unrealized loss position, fair value	240,038	245,005
Unrealized loss position, unrealized losses	$ (38,545)	(33,836)
Number of securities	236
Mortgage-Backed Security, Issued by US Government-Sponsored Enterprise [Member]
Unrealized loss position, fair value, less than 12 months	$ 0	0
Unrealized loss position, unrealized losses, less than 12 months	0	0
Unrealized loss position, fair value, more than 12 months	180,250	193,698
Unrealized loss position, unrealized losses, more than 12 months	(33,517)	(31,462)
Unrealized loss position, fair value	180,250	193,698
Unrealized loss position, unrealized losses	$ (33,517)	$ (31,462)
Number of securities	135