Note 12 - Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	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, 2018	Dec. 31, 2017	Dec. 31, 2016
Provision at federal statutory tax rate													$ 2,239	$ 3,589	$ 3,196
State income tax-net of federal tax benefit													109	96	111
Change in state statutory tax rate													(9)	(5)	(4)
Revaluation of net deferred tax asset due to change in federal income tax rate														290
Tax-exempt interest income													(328)	(507)	(416)
Bank-owned life insurance income													(67)	(73)	(62)
Captive insurance net premiums													(195)	(290)	(294)
Investment in tax credit entities													(272)
Other													(83)	3	(8)
Totals	$ 216	$ 530	$ 287	$ 361	$ 928	$ 825	$ 835	$ 515	$ 626	$ 666	$ 667	$ 564	$ 1,394	$ 3,103	$ 2,523
Effective tax rate													13.10%	29.40%	26.80%