Note 3 - Investment Securities - Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Due in 1 year or less, available for sale, amortized cost	$ 34,335
Due in 1 year or less, available for sale, fair value	34,157
Due in 1 year or less, held to maturity, amortized cost	4
Due in 1 year or less, held to maturity, fair value	4
After 1 year to 5 years, available for sale, amortized cost	102,194
After 1 year to 5 years, available for sale, fair value	102,007
After 1 year to 5 years, held to maturity, amortized cost	66,434
After 1 year to 5 years, held to maturity, fair value	67,983
After 5 years to 10 years, available for sale, amortized cost	32,017
After 5 years to 10 years, available for sale, fair value	32,099
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	96,116
After 10 years, available for sale, fair value	94,071
After 10 years, held to maturity, amortized cost	0
After 10 years, held to maturity, fair value	0
Total, available for sale, amortized cost	1,086,972	$ 527,188
Investment securities available for sale, at fair value	1,075,366	528,508
Investment securities held to maturity, amortized cost	1,660,292	814,936
Investment securities held to maturity, at fair value	1,647,360	836,972
Collateralized Mortgage Obligations [Member]
No specific maturity date, available for sale, amortized cost	375,570
No specific maturity date, available for sale, fair value	371,549
No specific maturity date, held to maturity, amortized cost	400,424
No specific maturity date, held to maturity, fair value	396,228
Total, available for sale, amortized cost	375,570	218,232
Investment securities available for sale, at fair value	371,549	221,546
Investment securities held to maturity, amortized cost	400,424	363,363
Investment securities held to maturity, at fair value	396,228	$ 375,819
Collateralized Mortgage-Backed Securities [Member]
No specific maturity date, available for sale, amortized cost	446,740
No specific maturity date, available for sale, fair value	441,483
No specific maturity date, held to maturity, amortized cost	1,193,430
No specific maturity date, held to maturity, fair value	$ 1,183,145