Acquisition of MainStreet - Narrative (Details) - USD ($)		1 Months Ended	3 Months Ended	9 Months Ended
	Jan. 01, 2015	Jan. 31, 2015	Sep. 30, 2015	Sep. 30, 2015	Dec. 31, 2011
Business Acquisition [Line Items]
Number of shares granted in conjunction with the acquisition				43,086
Accretion income				$ 1,437,000
MainStreet BankShares, Inc.
Business Acquisition [Line Items]
Shares received by acquiree entity in exchange of acquirer entity's common stock (in dollars per share)	$ 3.46
Shares received by acquiree entity in exchange of acquirer entity's common stock (in shares)	0.482
Shares exchange ratio on acquisition	64.30%
Cash dividends received for purchase of acquisition	$ 6,000,000
Amount of loan taken to fund merger	$ 0
Number of shares granted in conjunction with the acquisition	43,086
Amount of acquired loan portfolio	$ 122,447,000
Accretion income			$ 353,000
Acquired loan portfolio, at a fair value discount	7,397,000
Estimated fair value of performing portion of the portfolio	87,803,000
Deferred income taxes	2,773,000
Premises and equipment	1,030,000		$ 1,030,000	$ 1,030,000
Valuation adjustment due to acquisition	$ 290,000
Period valuation adjustment recognized over	12 months
Core deposits intangibles recognized due to the acquisition	$ 1,839,000
Amortization period of core deposit	10 years	120 months
Merger and acquisition expenses					$ 1,948,000