Loans and allowance for credit losses (Details 3) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013 Contracts	Sep. 30, 2012 Contracts
Number of contracts	13	31
Premodification outstanding recorded investment	$ 14,188	$ 28,023
Postmodification outstanding recorded investment	14,201	27,858
Related allowance	120	0
Troubled Debt Restructurings [Member] | Commercial Loan [Member]
Number of contracts	0	1
Premodification outstanding recorded investment	0	24
Postmodification outstanding recorded investment	0	24
Related allowance	0	0
Troubled Debt Restructurings [Member] | Consumer 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] | Residential Real Estate [Member]
Number of contracts	6	11
Premodification outstanding recorded investment	11,758	3,382
Postmodification outstanding recorded investment	11,772	3,044
Related allowance	38	0
Troubled Debt Restructurings [Member] | Commercial Real Estate [Member]
Number of contracts	4	7
Premodification outstanding recorded investment	2,212	7,270
Postmodification outstanding recorded investment	2,211	7,429
Related allowance	82	0
Troubled Debt Restructurings [Member] | Construction Loans [Member]
Number of contracts	3	12
Premodification outstanding recorded investment	218	17,347
Postmodification outstanding recorded investment	218	17,361
Related allowance	$ 0	$ 0