Note 11 - Restrictions on Dividends (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	$ 8,141	$ 9,071	$ 7,930
Payments of Dividends	$ 8,141	8,071	$ 7,930
Period of Restriction on Retained Net Income Without Prior Approval	2 years
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval	$ 20,820
National Bankshares Financial Services [Member]
Payments of Dividends		$ 350