Note 18 - Parent Company Financial Information (Details) - Condensed Statement of Cash Flows - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities
Net income	$ 489	$ 2,554	$ 2,386	$ 2,860	$ 2,269	$ 2,292	$ 2,098	$ 2,265	$ 8,289	$ 8,924	$ 8,233
Adjustments to reconcile net income to net cash provided by operating activities:
Net securities gains									(1,500)	(674)	(783)
Stock-based compensation expense									102	88	85
Increase (decrease) in other liabilities									421	469	(936)
Decrease (increase) in other assets									(887)	(363)	(71)
Deferred income tax (benefit) provision									2,322	(145)
Net cash provided by operating activities									16,162	11,332	9,116
Investing activities
Purchase of investment securities									(85,265)	(174,943)	(132,048)
Proceeds from sale of investment securities									42,509	32,573	47,960
Net cash used in investing activities									(91,182)	(53,991)	(47,762)
Financing activities
Cash dividend paid									(3,731)	(3,556)	(3,445)
Proceeds from issuance of common stock									672	862	648
Tax benefit from exercise of stock options										17	21
Net cash provided by (used in) financing activities									80,630	36,389	37,392
(Decrease) increase in cash and cash equivalents									5,610	(6,270)	(1,254)
Cash and cash equivalents at beginning of year				10,721				16,991	10,721	16,991	18,245
Cash and cash equivalents at end of period	16,331				10,721				16,331	10,721	16,991
Parent Company [Member]
Operating Activities
Net income									8,289	8,924	8,233
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed income from subsidiary									(4,102)	(5,548)	(4,650)
Net securities gains									(1,477)	(566)	(636)
Stock-based compensation expense									102	88	85
Increase (decrease) in other liabilities									335	(67)	(87)
Decrease (increase) in other assets									(3)	3	(2)
Deferred income tax (benefit) provision									98	14	13
Net cash provided by operating activities									3,242	2,848	2,956
Investing activities
Purchase of investment securities									(9,998)	(7,327)	(3,862)
Proceeds from sale of investment securities									14,422	7,137	3,713
Net cash used in investing activities									4,424	(190)	(149)
Financing activities
Cash dividend paid									(3,731)	(3,556)	(3,445)
Proceeds from issuance of common stock									672	862	648
Tax benefit from exercise of stock options										17	21
Net cash provided by (used in) financing activities									(3,059)	(2,677)	(2,776)
(Decrease) increase in cash and cash equivalents									4,607	(19)	31
Cash and cash equivalents at beginning of year				$ 60				$ 79	60	79	48
Cash and cash equivalents at end of period	$ 4,667				$ 60				$ 4,667	$ 60	$ 79