Note 11 - Fair Values - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities, Total	$ 0
Fair Value, Measurements, Recurring [Member]
Total	336,988,000	$ 335,742,000
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member]
Interest rate swap		(2,000)
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		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Total	331,797,000	330,551,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]
Interest rate swap		(2,000)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Total	5,191,000	5,191,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Swap [Member]
Interest rate swap		0
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member]
Available-for-sale Securities, Total	173,169,000	169,700,000
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities, Total	0	0
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities, Total	173,169,000	169,700,000
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities, Total	0	0
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member]
Available-for-sale Securities, Total	40,351,000	38,792,000
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities, Total	0	0
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities, Total	40,351,000	38,792,000
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities, Total	0	0
Fair Value, Measurements, Recurring [Member] | Municipal General Obligation Bonds [Member]
Available-for-sale Securities, Total	117,660,000	121,293,000
Fair Value, Measurements, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities, Total	0	0
Fair Value, Measurements, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities, Total	112,469,000	116,102,000
Fair Value, Measurements, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities, Total	5,191,000	5,191,000
Fair Value, Measurements, Recurring [Member] | Municipal Revenue Bonds [Member]
Available-for-sale Securities, Total	3,843,000	3,978,000
Fair Value, Measurements, Recurring [Member] | Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities, Total	0	0
Fair Value, Measurements, Recurring [Member] | Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities, Total	3,843,000	3,978,000
Fair Value, Measurements, Recurring [Member] | Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities, Total	0	0
Fair Value, Measurements, Recurring [Member] | Other Debt and Equity Securities [Member]
Available-for-sale Securities, Total	1,965,000	1,981,000
Fair Value, Measurements, Recurring [Member] | Other Debt and Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities, Total	0	0
Fair Value, Measurements, Recurring [Member] | Other Debt and Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities, Total	1,965,000	1,981,000
Fair Value, Measurements, Recurring [Member] | Other Debt and Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities, Total	$ 0	$ 0