Note 4 - Investments - Available for Sale and Held to Maturity Securities with Gross Unrealized Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Less Than Twelve Months, Fair Value	$ 339,657	$ 268,224
Less Than Twelve Months, Gross Unrealized Losses	20,626	4,788
Total, Fair Value	383,922	275,694
Total, Gross Unrealized Losses	27,274	5,156
Over Twelve Months, Fair Value	44,265	7,470
Over Twelve Months, Gross Unrealized Losses	6,648	368
US Treasury Securities [Member]
Less Than Twelve Months, Fair Value	78,806	73,154
Less Than Twelve Months, Gross Unrealized Losses	5,041	735
Total, Fair Value	78,806	73,154
Total, Gross Unrealized Losses	5,041	735
Collateralized Mortgage-Backed Securities [Member]
Less Than Twelve Months, Fair Value	39,678	26,288
Less Than Twelve Months, Gross Unrealized Losses	724	441
Total, Fair Value	47,932	26,288
Total, Gross Unrealized Losses	1,748	441
Over Twelve Months, Fair Value	8,254
Over Twelve Months, Gross Unrealized Losses	1,024
Collateralized Mortgage Obligations [Member]
Less Than Twelve Months, Fair Value	104,092	66,369
Less Than Twelve Months, Gross Unrealized Losses	3,569	1,035
Total, Fair Value	104,092	66,369
Total, Gross Unrealized Losses	3,569	1,035
US States and Political Subdivisions Debt Securities [Member]
Less Than Twelve Months, Fair Value	117,081	102,413
Less Than Twelve Months, Gross Unrealized Losses	11,292	2,577
Total, Fair Value	153,092	109,883
Total, Gross Unrealized Losses	16,916	2,945
Over Twelve Months, Fair Value	36,011	7,470
Over Twelve Months, Gross Unrealized Losses	$ 5,624	$ 368