Loans, net and allowance for loan losses - Major Classification of Loans by Past Due Status (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due
Total Past Due	$ 19,272	$ 18,805
Current	1,503,119	1,322,060
Total Loans	1,522,391	1,340,865
Loans > 90 Days and Accruing	1,110	763
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	3,953	6,086
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	2,285	1,585
Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due
Total Past Due	13,034	11,134
Commercial
Financing Receivable, Recorded Investment, Past Due
Total Past Due	2,704	1,758
Current	397,559	364,009
Total Loans	400,263	365,767
Commercial | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	531	126
Commercial | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	152
Commercial | Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due
Total Past Due	2,021	1,632
Real estate Commercial
Financing Receivable, Recorded Investment, Past Due
Total Past Due	8,878	5,388
Current	685,581	561,889
Total Loans	694,459	567,277
Real estate Commercial | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	1,310	1,364
Real estate Commercial | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	811	165
Real estate Commercial | Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due
Total Past Due	6,757	3,859
Real estate Residential
Financing Receivable, Recorded Investment, Past Due
Total Past Due	5,882	10,215
Current	288,150	296,003
Total Loans	294,032	306,218
Loans > 90 Days and Accruing	788	525
Real estate Residential | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	1,103	3,891
Real estate Residential | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	1,073	1,067
Real estate Residential | Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due
Total Past Due	3,706	5,257
Consumer
Financing Receivable, Recorded Investment, Past Due
Total Past Due	1,808	1,444
Current	131,829	100,159
Total Loans	133,637	101,603
Loans > 90 Days and Accruing	322	238
Consumer | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	1,009	705
Consumer | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	249	353
Consumer | Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due
Total Past Due	$ 550	$ 386