Loans and allowance for credit losses (Details 3) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014 Contracts	Jun. 30, 2013 Contracts
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts	0	6
Premodification outstanding recorded investment	$ 0	$ 1,380
Postmodification outstanding recorded investment	0	1,395
Related allowance	0	37
Troubled Debt Restructurings [Member] | Construction Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts	0	2
Premodification outstanding recorded investment	0	123
Postmodification outstanding recorded investment	0	123
Related allowance	0	0
Troubled Debt Restructurings [Member] | Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts	0	3
Premodification outstanding recorded investment	0	783
Postmodification outstanding recorded investment	0	798
Related allowance	0	37
Troubled Debt Restructurings [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts	0	1
Premodification outstanding recorded investment	0	474
Postmodification outstanding recorded investment	0	474
Related allowance	0	0
Troubled Debt Restructurings [Member] | Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts	0	0
Premodification outstanding recorded investment	0	0
Postmodification outstanding recorded investment	0	0
Related allowance	0	0
Troubled Debt Restructurings [Member] | Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts	0	0
Premodification outstanding recorded investment	0	0
Postmodification outstanding recorded investment	0	0
Related allowance	$ 0	$ 0