Loans and allowance for credit losses (Details 6) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Loans individually evaluated for impairment	$ 90,227		$ 72,510
Loans collectively evaluated for impairment	717,803		790,056
Total loans	808,030	841,050	862,566
Allowance for credit losses allocated to:
Loans individually evaluated for impairment	19		90
Loans collectively evaluated for impairment	12,936		13,540
Total allowance for credit losses	12,955	14,288	13,540
Unallocated Financing Receivables [Member]
Loans individually evaluated for impairment	0		0
Loans collectively evaluated for impairment	0		0
Total loans	0		0
Allowance for credit losses allocated to:
Loans individually evaluated for impairment	0		0
Loans collectively evaluated for impairment	0		246
Total allowance for credit losses	0		246
Commercial Loan [Member]
Loans individually evaluated for impairment	1,646		1,690
Loans collectively evaluated for impairment	59,885		69,792
Total loans	61,531	69,485	71,482
Allowance for credit losses allocated to:
Loans individually evaluated for impairment	0		0
Loans collectively evaluated for impairment	1,536		1,553
Total allowance for credit losses	1,536		1,553
Consumer Loan [Member]
Loans individually evaluated for impairment	54		40
Loans collectively evaluated for impairment	13,458		14,726
Total loans	13,512	14,639	14,766
Allowance for credit losses allocated to:
Loans individually evaluated for impairment	0		0
Loans collectively evaluated for impairment	304		610
Total allowance for credit losses	304		610
Residential Real Estate [Member]
Loans individually evaluated for impairment	19,671		19,944
Loans collectively evaluated for impairment	282,778		307,811
Total loans	302,449	321,604	327,755
Allowance for credit losses allocated to:
Loans individually evaluated for impairment	0		90
Loans collectively evaluated for impairment	4,187		3,952
Total allowance for credit losses	4,187		4,042
Commercial Real Estate [Member]
Loans individually evaluated for impairment	28,902		23,410
Loans collectively evaluated for impairment	292,915		298,134
Total loans	321,817	315,439	321,544
Allowance for credit losses allocated to:
Loans individually evaluated for impairment	0		0
Loans collectively evaluated for impairment	3,601		3,691
Total allowance for credit losses	3,601		3,691
Construction Loans [Member]
Loans individually evaluated for impairment	39,954		27,426
Loans collectively evaluated for impairment	68,767		99,593
Total loans	108,721	119,883	127,019
Allowance for credit losses allocated to:
Loans individually evaluated for impairment	19		0
Loans collectively evaluated for impairment	3,308		3,398
Total allowance for credit losses	$ 3,327		$ 3,398