Note 6 - Fair Value Measurements - Assets and Liabilities at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Securities available for sale, at fair value	$ 699,354	$ 686,080
Securities available for sale	699,354	686,080
Fair Value, Inputs, Level 1 [Member]
Securities available for sale, at fair value	0	0
Securities available for sale	0	0
Fair Value, Inputs, Level 2 [Member]
Securities available for sale, at fair value	699,354	686,080
Securities available for sale	699,354	686,080
Fair Value, Inputs, Level 3 [Member]
Securities available for sale, at fair value	0	0
Securities available for sale	0	0
US Treasury Securities [Member]
Securities available for sale, at fair value	964
Securities available for sale	964
US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale, at fair value	964
Securities available for sale	964
US Government Agencies Debt Securities [Member]
Securities available for sale, at fair value	322,388	278,019
Securities available for sale	322,388	278,019
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale, at fair value	0	0
Securities available for sale	0	0
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale, at fair value	322,388	278,019
Securities available for sale	322,388	278,019
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale, at fair value	0	0
Securities available for sale	0	0
US States and Political Subdivisions Debt Securities [Member]
Securities available for sale, at fair value	178,800	198,672
Securities available for sale	178,800	198,672
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale, at fair value	0	0
Securities available for sale	0	0
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale, at fair value	178,800	198,672
Securities available for sale	178,800	198,672
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale, at fair value	0	0
Securities available for sale	0	0
Collateralized Mortgage-Backed Securities [Member]
Securities available for sale, at fair value	190,886	206,174
Securities available for sale	190,886	206,174
Collateralized Mortgage-Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale, at fair value	0	0
Securities available for sale	0	0
Collateralized Mortgage-Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale, at fair value	190,886	206,174
Securities available for sale	190,886	206,174
Collateralized Mortgage-Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale, at fair value	0	0
Securities available for sale	0	0
Corporate Debt Securities [Member]
Securities available for sale, at fair value	6,316	3,215
Securities available for sale	6,316	3,215
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale, at fair value	0	0
Securities available for sale	0	0
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale, at fair value	6,316	3,215
Securities available for sale	6,316	3,215
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale, at fair value	0	0
Securities available for sale	$ 0	$ 0