Loans and allowance for credit losses (Details 5) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Loan Risk Rating	$ 718,627	$ 785,082
Pass [Member]
Loan Risk Rating	604,918	608,681
Special Mention [Member]
Loan Risk Rating	63,600	79,090
Substandard [Member]
Loan Risk Rating	32,608	60,345
Doubtful [Member]
Loan Risk Rating	0	492
Non Accrual [Member]
Loan Risk Rating	17,501	36,474
Commercial Loan [Member]
Loan Risk Rating	55,101	60,786
Commercial Loan [Member] | Pass [Member]
Loan Risk Rating	50,313	55,432
Commercial Loan [Member] | Special Mention [Member]
Loan Risk Rating	3,406	3,062
Commercial Loan [Member] | Substandard [Member]
Loan Risk Rating	714	1,639
Commercial Loan [Member] | Doubtful [Member]
Loan Risk Rating	0	59
Commercial Loan [Member] | Non Accrual [Member]
Loan Risk Rating	668	594
Consumer Loan [Member]
Loan Risk Rating	11,248	13,293
Consumer Loan [Member] | Pass [Member]
Loan Risk Rating	10,995	13,147
Consumer Loan [Member] | Special Mention [Member]
Loan Risk Rating	206	0
Consumer Loan [Member] | Substandard [Member]
Loan Risk Rating	0	59
Consumer Loan [Member] | Doubtful [Member]
Loan Risk Rating	0	0
Consumer Loan [Member] | Non Accrual [Member]
Loan Risk Rating	47	87
Residential Real Estate [Member]
Loan Risk Rating	280,153	288,011
Residential Real Estate [Member] | Pass [Member]
Loan Risk Rating	238,293	237,299
Residential Real Estate [Member] | Special Mention [Member]
Loan Risk Rating	21,806	23,657
Residential Real Estate [Member] | Substandard [Member]
Loan Risk Rating	14,649	15,090
Residential Real Estate [Member] | Doubtful [Member]
Loan Risk Rating	0	433
Residential Real Estate [Member] | Non Accrual [Member]
Loan Risk Rating	5,405	11,532
Commercial Real Estate [Member]
Loan Risk Rating	303,154	314,941
Commercial Real Estate [Member] | Pass [Member]
Loan Risk Rating	266,836	257,418
Commercial Real Estate [Member] | Special Mention [Member]
Loan Risk Rating	22,813	21,554
Commercial Real Estate [Member] | Substandard [Member]
Loan Risk Rating	10,163	21,402
Commercial Real Estate [Member] | Doubtful [Member]
Loan Risk Rating	0	0
Commercial Real Estate [Member] | Non Accrual [Member]
Loan Risk Rating	3,342	14,567
Construction Loans [Member]
Loan Risk Rating	68,971	108,051
Construction Loans [Member] | Pass [Member]
Loan Risk Rating	38,481	45,385
Construction Loans [Member] | Special Mention [Member]
Loan Risk Rating	15,369	30,817
Construction Loans [Member] | Substandard [Member]
Loan Risk Rating	7,082	22,155
Construction Loans [Member] | Doubtful [Member]
Loan Risk Rating	0	0
Construction Loans [Member] | Non Accrual [Member]
Loan Risk Rating	$ 8,039	$ 9,694