Note 4 - Securities (Details Textual) $ in Thousands	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Number of Temporarily Impaired Securities	529
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value	$ 639,367
Continuous Unrealized Loss Position Aggregate Losses	$ 40,595
Number of Temporarily Impaired Securities Greater than Twelve Months	116
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value	$ 114,273	$ 51,999
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses	14,880	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	614,894
Restricted Stock [Member]
Restricted Investments	$ 941	845
US Government Agencies Debt Securities [Member]
Number of Temporarily Impaired Securities	77
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value	$ 68,352
Continuous Unrealized Loss Position Aggregate Losses	8,570
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value	68,352	26,792
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses	$ 8,570	1,180
US States and Political Subdivisions Debt Securities [Member]
Number of Temporarily Impaired Securities	35
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value	$ 36,298	20,542
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses	$ 5,850	$ 793
Collateralized Mortgage-Backed Securities [Member]
Number of Temporarily Impaired Securities	4
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value	$ 9,623
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value	$ 460