Loans and allowance for credit losses (Details 3) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013 Contracts	Jun. 30, 2012 Contracts
Number of contracts	6	18
Premodification outstanding recorded investment	$ 1,380	$ 13,907
Postmodification outstanding recorded investment	1,395	13,753
Related allowance	37	0
Troubled Debt Restructurings [Member] | Commercial Loan [Member]
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]
Number of contracts	0	0
Premodification outstanding recorded investment		0
Postmodification outstanding recorded investment	0	0
Related allowance	0	0
Troubled Debt Restructurings [Member] | Residential Real Estate [Member]
Number of contracts	3	8
Premodification outstanding recorded investment	783	2,613
Postmodification outstanding recorded investment	798	2,276
Related allowance	37	0
Troubled Debt Restructurings [Member] | Commercial Real Estate [Member]
Number of contracts	1	3
Premodification outstanding recorded investment	474	5,351
Postmodification outstanding recorded investment	474	5,514
Related allowance	0	0
Troubled Debt Restructurings [Member] | Construction Loans [Member]
Number of contracts	2	7
Premodification outstanding recorded investment	123	5,943
Postmodification outstanding recorded investment	123	5,963
Related allowance	$ 0	$ 0