Note 2 - Investment Securities (Details Textual) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	77
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	$ 37,764		$ 37,087
Debt Securities, Available-for-sale, Realized Gain	69	$ 102
Debt Securities, Available-for-sale, Realized Loss	$ 9	$ 60
US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	30
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Total	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	$ 10,402		9,854
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	34
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Total	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	$ 20,323		23,010
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	5
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Total	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	$ 3,118		1,438
US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	8
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Total	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	$ 3,921		$ 2,785