Note 7 - Fair Value of Financial Instruments (Details) - Assets Measured On Recurring Basis - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Note 7 - Fair Value of Financial Instruments (Details) - Assets Measured On Recurring Basis [Line Items]
Available-for-sale securities	$ 752,036	$ 774,145
Fair Value, Measurements, Recurring [Member]
Note 7 - Fair Value of Financial Instruments (Details) - Assets Measured On Recurring Basis [Line Items]
Available-for-sale securities	752,036	774,145
US States and Political Subdivisions Debt Securities [Member]
Note 7 - Fair Value of Financial Instruments (Details) - Assets Measured On Recurring Basis [Line Items]
Available-for-sale securities	427,493	411,797
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Note 7 - Fair Value of Financial Instruments (Details) - Assets Measured On Recurring Basis [Line Items]
Available-for-sale securities	427,493	411,797
Pass-Through Mortgage Securities [Member]
Note 7 - Fair Value of Financial Instruments (Details) - Assets Measured On Recurring Basis [Line Items]
Available-for-sale securities	156,226	131,181
Pass-Through Mortgage Securities [Member] | Fair Value, Measurements, Recurring [Member]
Note 7 - Fair Value of Financial Instruments (Details) - Assets Measured On Recurring Basis [Line Items]
Available-for-sale securities	156,226	131,181
Collateralized Mortgage Obligations [Member]
Note 7 - Fair Value of Financial Instruments (Details) - Assets Measured On Recurring Basis [Line Items]
Available-for-sale securities	168,317	231,167
Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Note 7 - Fair Value of Financial Instruments (Details) - Assets Measured On Recurring Basis [Line Items]
Available-for-sale securities	168,317	231,167
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Note 7 - Fair Value of Financial Instruments (Details) - Assets Measured On Recurring Basis [Line Items]
Available-for-sale securities	752,036	774,145
Fair Value, Inputs, Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Note 7 - Fair Value of Financial Instruments (Details) - Assets Measured On Recurring Basis [Line Items]
Available-for-sale securities	427,493	411,797
Fair Value, Inputs, Level 2 [Member] | Pass-Through Mortgage Securities [Member] | Fair Value, Measurements, Recurring [Member]
Note 7 - Fair Value of Financial Instruments (Details) - Assets Measured On Recurring Basis [Line Items]
Available-for-sale securities	156,226	131,181
Fair Value, Inputs, Level 2 [Member] | Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Note 7 - Fair Value of Financial Instruments (Details) - Assets Measured On Recurring Basis [Line Items]
Available-for-sale securities	$ 168,317	$ 231,167