Note 10 - Restrictions on Dividends (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Consolidated Subsidiaries	$ 9,419	$ 8,141	$ 9,071
Payments of Dividends, Total	$ 8,419	$ 8,141	8,071
Period of Restriction on Retained Net Income Without Prior Approval	2 years
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval	$ 19,979
National Bankshares Financial Services [Member]
Payments of Dividends, Total			$ 350