Note 2 - Investment Securities - Investment Securities Available for Sale (Details) $ in Thousands	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Number of investment positions - less than twelve months	78	67
Fair value - less than twelve months	$ 54,539	$ 62,680
Gross unrealized losses - less than twelve months	$ 1,274	$ 590
Number of investment positions - more than twelve months	136	126
Fair value - more than twelve months	$ 163,341	$ 159,337
Gross unrealized losses - more than twelve months	$ 6,415	$ 3,391
Number of investment positions	214	193
Fair value	$ 217,880	$ 222,017
Gross unrealized losses	$ 7,689	$ 3,981
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Number of investment positions - less than twelve months	32	37
Fair value - less than twelve months	$ 22,976	$ 37,570
Gross unrealized losses - less than twelve months	$ 791	$ 400
Number of investment positions - more than twelve months	67	60
Fair value - more than twelve months	$ 77,551	$ 74,960
Gross unrealized losses - more than twelve months	$ 3,963	$ 1,853
Agency Collateralized Mortgage Obligations [Member]
Number of investment positions - less than twelve months	11	6
Fair value - less than twelve months	$ 6,688	$ 3,036
Gross unrealized losses - less than twelve months	$ 106	$ 38
Number of investment positions - more than twelve months	18	18
Fair value - more than twelve months	$ 10,628	$ 11,801
Gross unrealized losses - more than twelve months	$ 405	$ 300
US Government Agencies Debt Securities [Member]
Number of investment positions - less than twelve months	4	4
Fair value - less than twelve months	$ 9,579	$ 11,119
Gross unrealized losses - less than twelve months	$ 90	$ 69
Number of investment positions - more than twelve months	20	19
Fair value - more than twelve months	$ 59,416	$ 57,909
Gross unrealized losses - more than twelve months	$ 1,391	$ 916
Municipal Notes [Member]
Number of investment positions - less than twelve months	31	20
Fair value - less than twelve months	$ 15,296	$ 10,955
Gross unrealized losses - less than twelve months	$ 287	$ 83
Number of investment positions - more than twelve months	31	29
Fair value - more than twelve months	$ 15,746	$ 14,667
Gross unrealized losses - more than twelve months	$ 656	$ 322