Note 4 - Securities - Securities in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Less than 12 months, fair value	$ 51,556	$ 27,562
Less than 12 months, unrealized loss	(1,321)	(182)
12 months or more, fair value	39,554	43,661
12 months or more, unrealized loss	(1,962)	(1,073)
Total, fair value	91,110	71,223
Total, unrealized loss	(3,283)	(1,255)
US Treasury and Government [Member]
Less than 12 months, fair value
Less than 12 months, unrealized loss
12 months or more, fair value	4,395	4,472
12 months or more, unrealized loss	(139)	(69)
Total, fair value	4,395	4,472
Total, unrealized loss	(139)	(69)
US Government Agencies Debt Securities [Member]
Less than 12 months, fair value	7,796	3,447
Less than 12 months, unrealized loss	(134)	(42)
12 months or more, fair value	8,754	8,975
12 months or more, unrealized loss	(374)	(170)
Total, fair value	16,550	12,422
Total, unrealized loss	(508)	(212)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Less than 12 months, fair value	21,938	9,659
Less than 12 months, unrealized loss	(600)	(48)
12 months or more, fair value	5,726	6,581
12 months or more, unrealized loss	(262)	(105)
Total, fair value	27,664	16,240
Total, unrealized loss	(862)	(153)
Collateralized Mortgage Obligations [Member]
Less than 12 months, fair value	1,500	954
Less than 12 months, unrealized loss	(5)	(16)
12 months or more, fair value	15,870	19,147
12 months or more, unrealized loss	(997)	(692)
Total, fair value	17,370	20,101
Total, unrealized loss	(1,002)	(708)
US States and Political Subdivisions Debt Securities [Member]
Less than 12 months, fair value	17,386	10,510
Less than 12 months, unrealized loss	(514)	(60)
12 months or more, fair value	4,325	3,487
12 months or more, unrealized loss	(172)	(36)
Total, fair value	21,711	13,997
Total, unrealized loss	(686)	(96)
Corporate Debt Securities [Member]
Less than 12 months, fair value	2,936	2,992
Less than 12 months, unrealized loss	(68)	(16)
12 months or more, fair value	484	999
12 months or more, unrealized loss	(18)	(1)
Total, fair value	3,420	3,991
Total, unrealized loss	$ (86)	$ (17)