Loans and allowance for credit losses (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 Contracts	Mar. 31, 2013 Contracts
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts	0	4
Premodification outstanding recorded investment	$ 0	$ 648
Postmodification outstanding recorded investment	0	659
Related allowance	0	0
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	2
Premodification outstanding recorded investment	0	525
Postmodification outstanding recorded investment	0	536
Related allowance	0	0
Troubled Debt Restructurings [Member] | Commercial Real Estate [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] | 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