Loans and allowance for credit losses (Details 5) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Loan Risk Rating	$ 782,188	$ 785,082
Pass [Member]
Loan Risk Rating	613,470	608,681
Special Mention [Member]
Loan Risk Rating	75,945	79,090
Substandard [Member]
Loan Risk Rating	57,955	60,345
Doubtful [Member]
Loan Risk Rating	0	492
Non Accrual [Member]
Loan Risk Rating	34,818	36,474
Commercial Loan [Member]
Loan Risk Rating	56,448	60,786
Commercial Loan [Member] | Pass [Member]
Loan Risk Rating	50,938	55,432
Commercial Loan [Member] | Special Mention [Member]
Loan Risk Rating	4,097	3,062
Commercial Loan [Member] | Substandard [Member]
Loan Risk Rating	811	1,639
Commercial Loan [Member] | Doubtful [Member]
Loan Risk Rating	0	59
Commercial Loan [Member] | Non Accrual [Member]
Loan Risk Rating	602	594
Consumer Loan [Member]
Loan Risk Rating	11,539	13,293
Consumer Loan [Member] | Pass [Member]
Loan Risk Rating	11,433	13,147
Consumer Loan [Member] | Special Mention [Member]
Loan Risk Rating	52	0
Consumer Loan [Member] | Substandard [Member]
Loan Risk Rating	3	59
Consumer Loan [Member] | Doubtful [Member]
Loan Risk Rating	0	0
Consumer Loan [Member] | Non Accrual [Member]
Loan Risk Rating	51	87
Residential Real Estate [Member]
Loan Risk Rating	288,494	288,011
Residential Real Estate [Member] | Pass [Member]
Loan Risk Rating	235,008	237,299
Residential Real Estate [Member] | Special Mention [Member]
Loan Risk Rating	24,055	23,657
Residential Real Estate [Member] | Substandard [Member]
Loan Risk Rating	13,398	15,090
Residential Real Estate [Member] | Doubtful [Member]
Loan Risk Rating	0	433
Residential Real Estate [Member] | Non Accrual [Member]
Loan Risk Rating	16,033	11,532
Commercial Real Estate [Member]
Loan Risk Rating	321,191	314,941
Commercial Real Estate [Member] | Pass [Member]
Loan Risk Rating	268,053	257,418
Commercial Real Estate [Member] | Special Mention [Member]
Loan Risk Rating	23,752	21,554
Commercial Real Estate [Member] | Substandard [Member]
Loan Risk Rating	18,749	21,402
Commercial Real Estate [Member] | Doubtful [Member]
Loan Risk Rating	0	0
Commercial Real Estate [Member] | Non Accrual [Member]
Loan Risk Rating	10,637	14,567
Construction Loans [Member]
Loan Risk Rating	104,516	108,051
Construction Loans [Member] | Pass [Member]
Loan Risk Rating	48,038	45,385
Construction Loans [Member] | Special Mention [Member]
Loan Risk Rating	23,989	30,817
Construction Loans [Member] | Substandard [Member]
Loan Risk Rating	24,994	22,155
Construction Loans [Member] | Doubtful [Member]
Loan Risk Rating	0	0
Construction Loans [Member] | Non Accrual [Member]
Loan Risk Rating	$ 7,495	$ 9,694