Loans and reserve for credit losses (Reserve for Loan Losses and Recorded Investment in Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Total	$ 25,357	$ 25,290
Total loans	2,115,572	2,104,412
Allocated financing receivables
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Individually evaluated for impairment	2,000	2,000
Reserve for loan losses collectively evaluated for impairment	22,312	21,702
Reserve for loan losses Total	24,312	23,702
Recorded investment in loans Individually evaluated for impairment	7,392	7,674
Recorded investment in loans, collectively evaluated for impairment	2,108,180	2,096,738
Total loans	2,115,572	2,104,412
Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Total	1,045	1,588
Commercial real estate: \| Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Individually evaluated for impairment	0	0
Reserve for loan losses collectively evaluated for impairment	6,397	6,321
Reserve for loan losses Total	6,397	6,321
Recorded investment in loans Individually evaluated for impairment	490	640
Recorded investment in loans, collectively evaluated for impairment	1,004,616	1,002,968
Total loans	1,005,106	1,003,608
Construction \| Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Individually evaluated for impairment	0	0
Reserve for loan losses collectively evaluated for impairment	2,333	2,196
Reserve for loan losses Total	2,333	2,196
Recorded investment in loans Individually evaluated for impairment	0	0
Recorded investment in loans, collectively evaluated for impairment	216,259	211,038
Total loans	216,259	211,038
Residential real estate \| Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Individually evaluated for impairment	0	0
Reserve for loan losses collectively evaluated for impairment	3,409	3,325
Reserve for loan losses Total	3,409	3,325
Recorded investment in loans Individually evaluated for impairment	0	0
Recorded investment in loans, collectively evaluated for impairment	436,907	431,842
Total loans	436,907	431,842
Commercial and industrial \| Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Individually evaluated for impairment	2,000	2,000
Reserve for loan losses collectively evaluated for impairment	8,979	8,657
Reserve for loan losses Total	10,979	10,657
Recorded investment in loans Individually evaluated for impairment	6,902	7,034
Recorded investment in loans, collectively evaluated for impairment	407,833	407,402
Total loans	414,735	414,436
Consumer \| Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for loan losses Individually evaluated for impairment	0	0
Reserve for loan losses collectively evaluated for impairment	1,194	1,203
Reserve for loan losses Total	1,194	1,203
Recorded investment in loans Individually evaluated for impairment	0	0
Recorded investment in loans, collectively evaluated for impairment	42,565	43,488
Total loans	$ 42,565	$ 43,488

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The balance of financing receivables that were collectively evaluated for impairment.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

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

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