Note 12 - Fair Value Measurements - Available for Sale Investment Securities Measured at Fair Value on a Recurring Basis (Details) - USD ($)	Jun. 30, 2016	Dec. 31, 2015
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	128,187,000	106,906,000
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	0	0
US Government-sponsored Enterprises Debt Securities [Member]
Available-for-sale Securities	128,187,000	106,906,000
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	132,883,000	150,266,000
US States and Political Subdivisions 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	132,883,000	150,266,000
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	287,391,000	297,861,000
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	0	0
Residential Mortgage Backed Securities [Member]
Available-for-sale Securities	287,391,000	297,861,000
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	25,323,000	20,584,000
Commercial 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	25,323,000	20,584,000
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	5,865,000	5,840,000
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	0	0
Corporate Debt Securities [Member]
Available-for-sale Securities	5,865,000	5,840,000
Mutual Funds and Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	798,000	745,000
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
Mutual Funds and Equity Securities [Member]
Available-for-sale Securities	798,000	745,000
Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	798,000	745,000
Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	579,649,000	581,457,000
Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	0	0
Available-for-sale Securities	$ 580,447,000	$ 582,202,000