Loans, net and allowance for loan losses - Major Classification of Loans Portfolio Summarized by Credit Quality (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable
Loans, net	$ 1,559,867	$ 1,532,965
Commercial
Accounts, Notes, Loans and Financing Receivable
Loans, net	431,164	408,814
Real estate Commercial
Accounts, Notes, Loans and Financing Receivable
Loans, net	703,194	700,144
Real estate Residential
Accounts, Notes, Loans and Financing Receivable
Loans, net	286,389	289,781
Consumer
Accounts, Notes, Loans and Financing Receivable
Loans, net	139,120	134,226
Pass
Accounts, Notes, Loans and Financing Receivable
Loans, net	1,520,974	1,490,501
Pass | Commercial
Accounts, Notes, Loans and Financing Receivable
Loans, net	422,506	398,867
Pass | Real estate Commercial
Accounts, Notes, Loans and Financing Receivable
Loans, net	680,231	674,914
Pass | Real estate Residential
Accounts, Notes, Loans and Financing Receivable
Loans, net	279,384	282,737
Pass | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans, net	138,853	133,983
Special Mention
Accounts, Notes, Loans and Financing Receivable
Loans, net	15,312	16,847
Special Mention | Commercial
Accounts, Notes, Loans and Financing Receivable
Loans, net	4,698	6,222
Special Mention | Real estate Commercial
Accounts, Notes, Loans and Financing Receivable
Loans, net	10,409	10,392
Special Mention | Real estate Residential
Accounts, Notes, Loans and Financing Receivable
Loans, net	205	233
Substandard
Accounts, Notes, Loans and Financing Receivable
Loans, net	23,581	25,617
Substandard | Commercial
Accounts, Notes, Loans and Financing Receivable
Loans, net	3,960	3,725
Substandard | Real estate Commercial
Accounts, Notes, Loans and Financing Receivable
Loans, net	12,554	14,838
Substandard | Real estate Residential
Accounts, Notes, Loans and Financing Receivable
Loans, net	6,800	6,811
Substandard | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans, net	$ 267	$ 243