Borrowings - Narrative (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Line of Credit Facility [Line Items]
Remaining credit availability	$ 334,300,000
Letters of credit amount	25,000,000
Long-term debt	39,500,000
Federal Home Loan Bank borrowings	39,500,000	$ 85,000,000
Securities sold under agreements to repurchase, maturing the day following the day sold	34,900,000	$ 26,900,000
Federal Reserve Bank of Richmond [Member]
Line of Credit Facility [Line Items]
Line of credit, maximum credit limit	33,400,000.0
Revolving lines of credit, outstanding balance	0
Other Institutions [Member]
Line of Credit Facility [Line Items]
Line of credit, maximum credit limit	$ 45,000,000
Minimum [Member]
Line of Credit Facility [Line Items]
Federal Home Loan Bank advances, interest rate (in hundredths)	0.63%
Maximum [Member]
Line of Credit Facility [Line Items]
Federal Home Loan Bank advances, interest rate (in hundredths)	0.93%
Weighted Average [Member]
Line of Credit Facility [Line Items]
Federal Home Loan Bank advances, interest rate (in hundredths)	0.78%	0.66%