Note 6 - Fair Value Measurements - Assets and Liabilities at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Securities available for sale	$ 641,486	$ 546,742
Fair Value, Inputs, Level 2 [Member]
Securities available for sale	641,486	546,742
US Government Agencies Debt Securities [Member]
Securities available for sale	220,191	91,163
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	220,191	91,163
US States and Political Subdivisions Debt Securities [Member]
Securities available for sale	199,307	203,961
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	199,307	203,961
Collateralized Mortgage Backed Securities [Member]
Securities available for sale	218,752	249,175
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	218,752	249,175
Corporate Debt Securities [Member]
Securities available for sale	3,236	2,443
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	$ 3,236	$ 2,443