Loans and allowance for credit losses (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012 Numbers		Dec. 31, 2011 Numbers
Troubled Debt Restructurings [Member]
Number of contracts	73		50
Premodification outstanding recorded investment	$ 71,666		$ 40,395
Postmodification outstanding recorded investment	57,703		37,142
Troubled Debt Restructurings That Subsequently Defaulted [Member]
Number of contracts	28	[1]	18	[1]
Recorded investment	8,527	[1]	14,862	[1]
Commercial Loan [Member] | Troubled Debt Restructurings [Member]
Number of contracts	3		1
Premodification outstanding recorded investment	149		69
Postmodification outstanding recorded investment	126		69
Commercial Loan [Member] | Troubled Debt Restructurings That Subsequently Defaulted [Member]
Number of contracts	1	[1]	0	[1]
Recorded investment	36	[1]	0	[1]
Consumer Loan [Member] | Troubled Debt Restructurings [Member]
Number of contracts	1		0
Premodification outstanding recorded investment	30		0
Postmodification outstanding recorded investment	27		0
Consumer Loan [Member] | Troubled Debt Restructurings That Subsequently Defaulted [Member]
Number of contracts	1	[1]	0	[1]
Recorded investment	27	[1]	0	[1]
Residential Real Estate [Member] | Troubled Debt Restructurings [Member]
Number of contracts	28		20
Premodification outstanding recorded investment	14,145		11,471
Postmodification outstanding recorded investment	7,614		10,359
Residential Real Estate [Member] | Troubled Debt Restructurings That Subsequently Defaulted [Member]
Number of contracts	13	[1]	10	[1]
Recorded investment	2,902	[1]	7,353	[1]
Commercial Real Estate [Member] | Troubled Debt Restructurings [Member]
Number of contracts	22		20
Premodification outstanding recorded investment	24,065		15,874
Postmodification outstanding recorded investment	20,418		14,175
Commercial Real Estate [Member] | Troubled Debt Restructurings That Subsequently Defaulted [Member]
Number of contracts	6	[1]	5	[1]
Recorded investment	3,433	[1]	6,751	[1]
Construction Loans [Member] | Troubled Debt Restructurings [Member]
Number of contracts	19		9
Premodification outstanding recorded investment	33,277		12,981
Postmodification outstanding recorded investment	29,518		12,539
Construction Loans [Member] | Troubled Debt Restructurings That Subsequently Defaulted [Member]
Number of contracts	7	[1]	3	[1]
Recorded investment	$ 2,129	[1]	$ 758	[1]

[1] Generally, a loan is considered in default when principal or interest is past due 30 days or more.