Loans and allowance for credit losses (Details 4) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013 Contracts		Sep. 30, 2012 Contracts
Number of contracts	5	[1]	4	[2]
Recorded investment	$ 3,304	[1]	$ 1,579	[2]
Related allowance	74	[1]	0	[2]
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Commercial Loan [Member]
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]
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]
Number of contracts	4	[1]	3	[2]
Recorded investment	1,563	[1]	913	[2]
Related allowance	0	[1]	0	[2]
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Commercial Real Estate [Member]
Number of contracts	1	[1]	0	[2]
Recorded investment	1,741	[1]	0	[2]
Related allowance	74	[1]	0	[2]
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Construction Loans [Member]
Number of contracts	0	[1]	1	[2]
Recorded investment	0	[1]	666	[2]
Related allowance	$ 0	[1]	$ 0	[2]

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

[2] These loans were classified as TDRs during 2011.