Investments (Narrative) (Details) - USD ($)	1 Months Ended	3 Months Ended
	Jan. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Schedule of Investments [Line Items]
Federal Home Loan Bank Stock and Federal Reserve Bank Stock		$ 15,400,000		$ 15,500,000
Non-governmental issues exceeding 10% shareholders equity threshold		0		0
Credit-related investment impairment losses		0	$ 0
Sale of VISA shares		0	$ 17,837,000
Asset Pledged as Collateral
Schedule of Investments [Line Items]
Carrying value of securities pledged		641,000,000		644,000,000
Marketable equity securities
Schedule of Investments [Line Items]
Investment securities		$ 11,800,000		$ 11,800,000
VISA, Inc. (VISA)
Schedule of Investments [Line Items]
Sale of VISA shares	$ 17,800,000
VISA, Inc. (VISA) | Common Class B
Schedule of Investments [Line Items]
Shares of Visa Inc. Class B common shares sold (in shares)	86,605
VISA, Inc. (VISA) | Marketable equity securities
Schedule of Investments [Line Items]
Investment securities	$ 0
Maximum | First National Corporation (FXNC)
Schedule of Investments [Line Items]
Equity ownership positions in the community bank holding companies (percent)		3.70%
Maximum | Eagle Financial Services, Inc. (EFSI)
Schedule of Investments [Line Items]
Equity ownership positions in the community bank holding companies (percent)		1.50%