Note 6 - Investment Securities - Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Due in 1 year or less, available for sale, amortized cost	$ 35,899
Due in 1 year or less, available for sale, fair value	29,762
Due in 1 year or less, held to maturity, amortized cost	0
Due in 1 year or less, held to maturity, fair value	0
After 1 year to 5 years, available for sale, amortized cost	95,090
After 1 year to 5 years, available for sale, fair value	89,803
After 1 year to 5 years, held to maturity, amortized cost	52,788
After 1 year to 5 years, held to maturity, fair value	48,024
After 5 years to 10 years, available for sale, amortized cost	67,549
After 5 years to 10 years, available for sale, fair value	60,572
After 5 years to 10 years, held to maturity, amortized cost	0
After 5 years to 10 years, held to maturity, fair value	0
After 10 years, available for sale, amortized cost	106,238
After 10 years, available for sale, fair value	82,347
After 10 years, held to maturity, amortized cost	0
After 10 years, held to maturity, fair value	0
Total, available for sale, amortized cost	1,203,064	$ 1,086,972
Investment securities available for sale, at fair value	999,521	1,075,366
Investment securities held to maturity, amortized cost	1,562,376	1,660,292
Investment securities held to maturity, at fair value	1,267,546	1,647,360
Collateralized Mortgage Obligations [Member]
No specific maturity date, available for sale, amortized cost	388,019
No specific maturity date, available for sale, fair value	321,015
No specific maturity date, held to maturity, amortized cost	374,421
No specific maturity date, held to maturity, fair value	306,864
Total, available for sale, amortized cost	388,019	375,570
Investment securities available for sale, at fair value	321,015	371,549
Investment securities held to maturity, amortized cost	374,421	400,424
Investment securities held to maturity, at fair value	306,864	$ 396,228
Collateralized Mortgage-Backed Securities [Member]
No specific maturity date, available for sale, amortized cost	510,269
No specific maturity date, available for sale, fair value	416,022
No specific maturity date, held to maturity, amortized cost	1,135,167
No specific maturity date, held to maturity, fair value	$ 912,658