Note 7 - Fair Value Measurements - Assets and Liabilities at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Securities available for sale	$ 439,019	$ 435,263
Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0	0
Fair Value, Inputs, Level 2 [Member]
Securities available for sale	439,019	435,263
Fair Value, Inputs, Level 3 [Member]
Securities available for sale	0	0
US Government Agencies Debt Securities [Member]
Securities available for sale	101,607	121,123
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0	0
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	101,607	121,123
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	0	0
US States and Political Subdivisions Debt Securities [Member]
Securities available for sale	102,297	88,239
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0	0
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	102,297	88,239
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	0	0
Collateralized Mortgage Backed Securities [Member]
Securities available for sale	230,989	221,783
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0	0
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	230,989	221,783
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	0	0
Corporate Debt Securities [Member]
Securities available for sale	4,126	4,118
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0	0
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	4,126	4,118
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	$ 0	$ 0