Note 3 - Securities - Securities Available-for-sale With Unrealized Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Less than 12 Months - Fair Value	$ 54,648	$ 44,331
Less than 12 Months - Unrealized Loss	(1,338)	(531)
12 Months or More - Fair Value	39,544	38,326
12 Months or More - Unrealized Loss	(1,715)	(1,099)
Fair Value	94,192	82,657
Unrealized Loss	(3,053)	(1,630)
US Government-sponsored Enterprises Debt Securities [Member]
Less than 12 Months - Fair Value	3,882	6,910
Less than 12 Months - Unrealized Loss	(126)	(97)
12 Months or More - Fair Value	9,434	6,563
12 Months or More - Unrealized Loss	(110)	(52)
Fair Value	13,316	13,473
Unrealized Loss	(236)	(149)
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Less than 12 Months - Fair Value	50,766	37,421
Less than 12 Months - Unrealized Loss	(1,212)	(434)
12 Months or More - Fair Value	30,110	31,763
12 Months or More - Unrealized Loss	(1,605)	(1,047)
Fair Value	80,876	69,184
Unrealized Loss	$ (2,817)	$ (1,481)