Loans Loans (Summary of Change in Accretable Yield PCI Loans (Details) - Purchased Impaired Loans [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of Change in Accretable Yield PCI Loans [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield	$ 745	$ 290	$ 0
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Accretion	(162)	(20)
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Reclassifications from Nonaccretable Difference	(31)	0
Certain Loans Acquired in Transfer Not Accounting for as Debt Securities Accretable Yield Other Changes, Net	(13)	(23)
Highland County Bankshares, Inc [Member]
Summary of Change in Accretable Yield PCI Loans [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Additions	0	333
First Century Bankshares, Inc [Member]
Summary of Change in Accretable Yield PCI Loans [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Additions	$ 661	$ 0