Loans and allowance for credit losses (Details 4) (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	[1]	3	[2]
Recorded investment	$ 0	[1]	$ 1,918	[2]
Related allowance	0	[1]	74	[2]
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Construction Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts	0	[1]	0	[2]
Recorded investment	0	[1]	0	[2]
Related allowance	0	[1]	0	[2]
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts	0	[1]	2	[2]
Recorded investment	0	[1]	177	[2]
Related allowance	0	[1]	0	[2]
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts	0	[1]	1	[2]
Recorded investment	0	[1]	1,741	[2]
Related allowance	0	[1]	74	[2]
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts	0	[1]	0	[2]
Recorded investment	0	[1]	0	[2]
Related allowance	0	[1]	0	[2]
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts	0	[1]	0	[2]
Recorded investment	0	[1]	0	[2]
Related allowance	$ 0	[1]	$ 0	[2]

[1] These loans were classified as TDRs during 2013.

[2] These loans were classified as TDRs during 2012.