Loans and reserve for credit losses (Schedule of Financing Receivables, Non Accrual Status) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-accrual loans	$ 12,141	$ 13,695
Total accruing loans which are contractually past due 90 days or more	624	17
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accruing loans which are contractually past due 90 days or more	583	0
Commercial real estate: | Owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-accrual loans	2,337	1,739
Commercial real estate: | Non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-accrual loans	278	2,659
Commercial real estate: | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-accrual loans	2,615	4,398
Construction | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-accrual loans	409	429
Residential real estate | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-accrual loans	1,411	1,598
Commercial and industrial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-accrual loans	7,706	7,270
Total accruing loans which are contractually past due 90 days or more	12	5
Consumer | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-accrual loans	0	0
Total accruing loans which are contractually past due 90 days or more	$ 29	$ 12