Note 4 - Securities (Details Textual) $ in Thousands	Sep. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Number of Temporarily Impaired Securities	614
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value	$ 647,648
Continuous Unrealized Loss Position Aggregate Losses	$ 108,057
Number of Temporarily Impaired Securities Greater than Twelve Months	207
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value	$ 182,187	$ 51,999
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses	50,582	2,145
National Bank of Blacksburg [Member] | Federal Home Loan Bank of Atlanta [Member]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	641,798
Restricted Stock [Member]
Restricted Investments	$ 941	845
US Government Agencies Debt Securities [Member]
Number of Temporarily Impaired Securities	150
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value	$ 124,968
Continuous Unrealized Loss Position Aggregate Losses	31,692
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value	124,968	26,792
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses	$ 31,692	1,180
US States and Political Subdivisions Debt Securities [Member]
Number of Temporarily Impaired Securities	50
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value	$ 43,622
Continuous Unrealized Loss Position Aggregate Losses	17,482
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value	43,622	20,542
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses	$ 17,482	793
Commercial Mortgage-Backed Securities [Member]
Number of Temporarily Impaired Securities	6
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value	$ 12,802
Continuous Unrealized Loss Position Aggregate Losses	1,200
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value	12,802	4,665
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses	$ 1,200	172
Corporate Debt Securities [Member]
Number of Temporarily Impaired Securities	1
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value	$ 795
Continuous Unrealized Loss Position Aggregate Losses	208
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value	795	0
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses	$ 208	$ 0