Note 18 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale Securities	$ 335,744,000	$ 328,060,000
Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	0
US Government Agencies Debt Securities [Member]
Available-for-sale Securities	169,700,000	152,040,000
Collateralized Mortgage Backed Securities [Member]
Available-for-sale Securities	38,792,000	47,392,000
Municipal General Obligation Bonds [Member]
Available-for-sale Securities	121,293,000	119,047,000
Municipal Revenue Bonds [Member]
Available-for-sale Securities	3,978,000	7,631,000
Other Debt and Equity Securities [Member]
Available-for-sale Securities	1,981,000	1,950,000
Fair Value, Measurements, Recurring [Member]
Total	335,742,000	327,976,000
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member]
Interest rate swap agreement	(2,000)	(84,000)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Total	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Interest Rate Swap [Member]
Interest rate swap agreement	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Total	330,551,000	321,577,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]
Interest rate swap agreement	(2,000)	(84,000)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Total	5,191,000	6,399,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Swap [Member]
Interest rate swap agreement	0	0
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member]
Available-for-sale Securities	169,700,000	152,040,000
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	169,700,000	152,040,000
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member]
Available-for-sale Securities	38,792,000	47,392,000
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	38,792,000	47,392,000
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Municipal General Obligation Bonds [Member]
Available-for-sale Securities	121,293,000	119,047,000
Fair Value, Measurements, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	116,102,000	112,648,000
Fair Value, Measurements, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	5,191,000	6,399,000
Fair Value, Measurements, Recurring [Member] | Municipal Revenue Bonds [Member]
Available-for-sale Securities	3,978,000	7,631,000
Fair Value, Measurements, Recurring [Member] | Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	3,978,000	7,631,000
Fair Value, Measurements, Recurring [Member] | Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Other Debt and Equity Securities [Member]
Available-for-sale Securities	1,981,000	1,950,000
Fair Value, Measurements, Recurring [Member] | Other Debt and Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Other Debt and Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	1,981,000	1,950,000
Fair Value, Measurements, Recurring [Member] | Other Debt and Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	$ 0	$ 0