Loans and allowance for credit losses (Details 3) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Loan Risk Rating	$ 808,030	$ 841,050	$ 862,566
Pass [Member]
Loan Risk Rating	612,218	643,258
Special Mention [Member]
Loan Risk Rating	90,413	63,686
Substandard [Member]
Loan Risk Rating	65,464	82,214
Doubtful [Member]
Loan Risk Rating	493	522
Non Accrual [Member]
Loan Risk Rating	39,442	51,370
Commercial Loan [Member]
Loan Risk Rating	61,531	69,485	71,482
Commercial Loan [Member] | Pass [Member]
Loan Risk Rating	54,488	59,178
Commercial Loan [Member] | Special Mention [Member]
Loan Risk Rating	3,870	3,813
Commercial Loan [Member] | Substandard [Member]
Loan Risk Rating	1,556	4,748
Commercial Loan [Member] | Doubtful [Member]
Loan Risk Rating	60	77
Commercial Loan [Member] | Non Accrual [Member]
Loan Risk Rating	1,557	1,669
Consumer Loan [Member]
Loan Risk Rating	13,512	14,639	14,766
Consumer Loan [Member] | Pass [Member]
Loan Risk Rating	13,252	14,520
Consumer Loan [Member] | Special Mention [Member]
Loan Risk Rating	120	32
Consumer Loan [Member] | Substandard [Member]
Loan Risk Rating	86	59
Consumer Loan [Member] | Doubtful [Member]
Loan Risk Rating	0	0
Consumer Loan [Member] | Non Accrual [Member]
Loan Risk Rating	54	28
Residential Real Estate [Member]
Loan Risk Rating	302,449	321,604	327,755
Residential Real Estate [Member] | Pass [Member]
Loan Risk Rating	246,805	261,910
Residential Real Estate [Member] | Special Mention [Member]
Loan Risk Rating	24,191	13,467
Residential Real Estate [Member] | Substandard [Member]
Loan Risk Rating	16,580	25,676
Residential Real Estate [Member] | Doubtful [Member]
Loan Risk Rating	433	445
Residential Real Estate [Member] | Non Accrual [Member]
Loan Risk Rating	14,440	20,106
Commercial Real Estate [Member]
Loan Risk Rating	321,817	315,439	321,544
Commercial Real Estate [Member] | Pass [Member]
Loan Risk Rating	254,339	257,247
Commercial Real Estate [Member] | Special Mention [Member]
Loan Risk Rating	30,873	16,001
Commercial Real Estate [Member] | Substandard [Member]
Loan Risk Rating	24,689	28,179
Commercial Real Estate [Member] | Doubtful [Member]
Loan Risk Rating	0	0
Commercial Real Estate [Member] | Non Accrual [Member]
Loan Risk Rating	11,916	14,012
Construction Loans [Member]
Loan Risk Rating	108,721	119,883	127,019
Construction Loans [Member] | Pass [Member]
Loan Risk Rating	43,334	50,403
Construction Loans [Member] | Special Mention [Member]
Loan Risk Rating	31,359	30,373
Construction Loans [Member] | Substandard [Member]
Loan Risk Rating	22,553	23,552
Construction Loans [Member] | Doubtful [Member]
Loan Risk Rating	0	0
Construction Loans [Member] | Non Accrual [Member]
Loan Risk Rating	$ 11,475	$ 15,555