Note 8 - Long-term Borrowings (Details Textual)		3 Months Ended	21 Months Ended
	Apr. 07, 2006 USD ($)	Mar. 31, 2021 USD ($)	Dec. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Apr. 01, 2019 USD ($)	Jul. 01, 2011 USD ($)
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged		$ 897,492,000
Long-term Federal Home Loan Bank Advances, Total		0		$ 0
Public Deposit Accounts		311,702,000
Subordinated Debt, Ending Balance		$ 35,656,000		35,630,000
Subordinated Borrowing, Interest Rate		5.35%	6.75%
Proceeds from Issuance of Long-term Debt, Total	$ 20,000,000
Number of Consecutive Quarterly Periods for Deferral of Distributions on Trust Preferred Securities, Maximum	20
Proceeds from Issuance of Common Stock	$ 619,000
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust, Total	$ 20,619,000
MidCarolina Trusts [Member]
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust, Total						$ 8,764,000
Equity Method Investments		$ 264,000
AMNB Statutory Trust I [Member]
Equity Method Investments		619,000
MidCarolina Trust I [Member]
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust, Fair Value Adjustment		652,000		666,000		1,197,000
MidCarolina Trust II [Member]
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust, Fair Value Adjustment		575,000		$ 587,000		$ 1,021,000
HomeTown Bankshares Corporation [Member]
Subordinated Debt, Ending Balance					$ 7,500,000
US States and Political Subdivisions Debt Securities [Member]
Deposit Liabilities, Collateral Issued, Financial Instruments		$ 133,057,000
FHLB Line of Credit [Member]
Debt Instrument, Percentage of Assets		30.00%
Letters of Credit Outstanding, Amount		$ 245,000,000
Subordinated Debt [Member] | HomeTown Bankshares Corporation [Member]
Liabilities, Fair Value Adjustment			$ 30,000