Guarantees (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Commitments to Extend Credit
Loan Commitments and Letters of Credit [Line Items]
Notional Amount	$ 328,774	$ 315,256	$ 294,618
Fair Value	0	0	0
Standby Letters of Credit
Loan Commitments and Letters of Credit [Line Items]
Notional Amount	3,584	3,526	3,371
Fair Value	$ 24	$ 23	$ 28
Minimum | Standby Letters of Credit
Loan Commitments and Letters of Credit [Line Items]
Loan commitments, fixed fee percent	1.00%
Maximum | Standby Letters of Credit
Loan Commitments and Letters of Credit [Line Items]
Loan commitments, fixed fee percent	3.00%