Note 12 - Fair Value Measurements - Available for Sale Investment Securities Measured At Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Available-for-sale Securities	$ 492,906	$ 480,864
Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	861	833
Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	492,045	480,031
Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	0	0
US Government-sponsored Enterprises Debt Securities [Member]
Available-for-sale Securities	94,883	71,694
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	0	0
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	94,883	71,694
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	0	0
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale Securities	129,595	132,292
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	0	0
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	129,595	132,292
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	0	0
Residential Mortgage Backed Securities [Member]
Available-for-sale Securities	212,639	224,307
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	0	0
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	212,639	224,307
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	0	0
Commercial Mortgage Backed Securities [Member]
Available-for-sale Securities	47,535	45,613
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	0	0
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	47,535	45,613
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	0	0
Corporate Debt Securities [Member]
Available-for-sale Securities	7,393	6,125
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	0	0
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	7,393	6,125
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	0	0
Mutual Funds and Equity Securities [Member]
Available-for-sale Securities	861	833
Mutual Funds and Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	861	833
Mutual Funds and Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	0	0
Mutual Funds and Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	$ 0	$ 0