Allowance for Loan Losses - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) loan_class	Dec. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of classes in the loan portfolio (loan class) | loan_class	8
Allowance for loan and lease losses (percent)	0.45%
Allowance for loan and lease losses, period increase (decrease)	$ 105
Allowance for loan losses	$ 10,957	$ 10,729	$ 10,367	$ 10,138
Allowance for loan losses as a percent of total loans	0.92%		0.95%
Number of classes in the commercial loan portfolio (loan class) | loan_class	3
Residential loans typical loan to value range, maximum (percent)	80.00%
Construction loans accrual to company capital	36.00%
Constructions loan portfolio maximum to company capital	100.00%
Construction and non owner occupied commercial real estate	131.40%
Maximum loan portfolio to company capital	300.00%
Outstanding loans and commitments subject by independent consulting firm	50.00%
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$ 581	545	$ 573	$ 559
Delinquent period before consumer loans charged off (days)	120 days
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Delinquent period before residential loans placed on non accrual status (days)	90 days
Delinquent period for loans charged off (days)	180 days
Delinquency period for loans charged off after receipt of notification from bankruptcy court (days)	60 days
Unallocated Reserves
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$ 811	$ 642	$ 1,591
Total reserve allowance accounted for by loan loss allowances (percent)	7.40%	6.00%