Note 4 - Securities (Details Textual) $ in Thousands	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Number of Temporarily Impaired Securities	229
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value	$ 254,651
Continuous Unrealized Loss Position Aggregate Losses	$ 5,644
Number of Temporarily Impaired Securities Greater than Twelve Months	10
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value	$ 15,116	$ 4,695
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses	513	5
National Bank of Blacksburg [Member] | Federal Home Loan Bank of Atlanta [Member]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	596,772
Restricted Stock [Member]
Restricted Investments	$ 845	1,279
US Government Agencies Debt Securities [Member]
Number of Temporarily Impaired Securities	1
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value	$ 944
Continuous Unrealized Loss Position Aggregate Losses	53
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value	944	0
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses	$ 53	0
US States and Political Subdivisions Debt Securities [Member]
Number of Temporarily Impaired Securities	6
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value	$ 9,026	635
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses	$ 313	$ 3
Collateralized Mortgage Backed Securities [Member]
Number of Temporarily Impaired Securities	3
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value	$ 5,146
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value	$ 147