Loans - Nonaccrual Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Schedule of Financing Receivables [Line Items]
Nonaccrual loans	$ 14,283	$ 14,736	$ 8,500
Commercial | Real estate
Schedule of Financing Receivables [Line Items]
Nonaccrual loans	1,021	752	2,625
Commercial | Construction
Schedule of Financing Receivables [Line Items]
Nonaccrual loans	0	0	0
Commercial | Other
Schedule of Financing Receivables [Line Items]
Nonaccrual loans	8,895	9,357	938
Municipal
Schedule of Financing Receivables [Line Items]
Nonaccrual loans	0	0	0
Residential | Construction
Schedule of Financing Receivables [Line Items]
Nonaccrual loans	0	0	0
Residential | Term
Schedule of Financing Receivables [Line Items]
Nonaccrual loans	3,654	3,778	4,028
Home equity line of credit
Schedule of Financing Receivables [Line Items]
Nonaccrual loans	697	833	909
Consumer
Schedule of Financing Receivables [Line Items]
Nonaccrual loans	$ 16	$ 16	$ 0