Loans, net and allowance for loan losses - Major Classification of Loans by Past Due Status (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due
Total Past Due	$ 14,647	$ 21,260
Current	1,617,868	1,511,705
Total Loans	1,632,515	1,532,965
Loans > 90 Days and Accruing	1,510	844
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	3,693	8,093
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	723	1,215
Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due
Total Past Due	10,231	11,952
Commercial
Financing Receivable, Recorded Investment, Past Due
Total Past Due	1,607	1,258
Current	447,857	407,556
Total Loans	449,464	408,814
Commercial \| 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	260	249
Commercial \| 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	84	75
Commercial \| Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due
Total Past Due	1,263	934
Real estate Commercial
Financing Receivable, Recorded Investment, Past Due
Total Past Due	5,199	12,325
Current	746,311	687,819
Total Loans	751,510	700,144
Real estate Commercial \| 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	831	4,782
Real estate Commercial \| 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	135	527
Real estate Commercial \| Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due
Total Past Due	4,233	7,016
Real estate Residential
Financing Receivable, Recorded Investment, Past Due
Total Past Due	6,215	6,015
Current	283,367	283,766
Total Loans	289,582	289,781
Loans > 90 Days and Accruing	1,281	558
Real estate Residential \| 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	1,756	2,100
Real estate Residential \| 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	147	354
Real estate Residential \| Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due
Total Past Due	4,312	3,561
Consumer
Financing Receivable, Recorded Investment, Past Due
Total Past Due	1,626	1,662
Current	140,333	132,564
Total Loans	141,959	134,226
Loans > 90 Days and Accruing	229	286
Consumer \| 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	846	962
Consumer \| 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	357	259
Consumer \| Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due
Total Past Due	$ 423	$ 441

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

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- Definition

Financing receivables that are current.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953401-111524

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Recorded Investment in financing receivables that are past due at the balance sheet date.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

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