Loans and allowance for credit losses (Details 6) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Loans individually evaluated for impairment	$ 85,189		$ 48,476
Loans collectively evaluated for impairment	724,769		828,855
Total loans	809,958	841,050	877,331
Allowance for credit losses allocated to:
Loans individually evaluated for impairment	920		1,362
Loans collectively evaluated for impairment	12,070		14,996
Allowance for credit losses	12,990	14,288	16,358
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	408		75
Allowance for credit losses	408		75
Commercial Loan [Member]
Loans individually evaluated for impairment	1,677		2,990
Loans collectively evaluated for impairment	61,327		71,495
Total loans	63,004	69,485	74,485
Allowance for credit losses allocated to:
Loans individually evaluated for impairment	0		567
Loans collectively evaluated for impairment	1,063		2,143
Allowance for credit losses	1,063		2,710
Consumer Loan [Member]
Loans individually evaluated for impairment	55		29
Loans collectively evaluated for impairment	14,095		15,236
Total loans	14,150	14,639	15,265
Allowance for credit losses allocated to:
Loans individually evaluated for impairment	0		0
Loans collectively evaluated for impairment	485		605
Allowance for credit losses	485		605
Residential Real Estate [Member]
Loans individually evaluated for impairment	25,408		12,187
Loans collectively evaluated for impairment	280,685		319,947
Total loans	306,093	321,604	332,134
Allowance for credit losses allocated to:
Loans individually evaluated for impairment	420		289
Loans collectively evaluated for impairment	3,817		3,895
Allowance for credit losses	4,237		4,184
Commercial Real Estate [Member]
Loans individually evaluated for impairment	26,713		15,141
Loans collectively evaluated for impairment	288,931		312,166
Total loans	315,644	315,439	327,307
Allowance for credit losses allocated to:
Loans individually evaluated for impairment	500		506
Loans collectively evaluated for impairment	3,452		4,745
Allowance for credit losses	3,952		5,251
Construction Loans [Member]
Loans individually evaluated for impairment	31,336		18,129
Loans collectively evaluated for impairment	79,731		110,011
Total loans	111,067	119,883	128,140
Allowance for credit losses allocated to:
Loans individually evaluated for impairment	0		0
Loans collectively evaluated for impairment	2,845		3,533
Allowance for credit losses	$ 2,845		$ 3,533