Long-term Borrowings (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016		Jul. 31, 2011
Debt Disclosure [Abstract]
Percentage of entity's assets equal to line of credit facility	30.00%
Collateral pledged under blanket floating lien agreement	$ 508,165,000
Long term advances with federal home loan bank [Abstract]
Advance Amount	9,996,000	$ 9,980,000	[1]
Advances due, net of fair value discount	4,000
Public deposit accounts	$ 221,018,000
MainStreet BankShares, Inc.
Long term advances with federal home loan bank [Abstract]
Long-term borrowings acquired				$ 0
Amount of loan taken to fund merger				$ 0
November 2017
Long term advances with federal home loan bank [Abstract]
Due by	Nov. 30, 2017	Nov. 30, 2017
Advance Amount	$ 9,996,000	$ 9,980,000
November 2017 | Weighted Average
Long term advances with federal home loan bank [Abstract]
Weighted Average Rate	2.98%	2.98%
Federal Home Loan Bank Advances
Long term advances with federal home loan bank [Abstract]
Outstanding letters of credit	$ 190,700,000
US government and agency securities
Long term advances with federal home loan bank [Abstract]
Outstanding letters of credit	$ 68,756,000

[1] Derived from audited consolidated financial statements.