Loans and reserve for credit losses (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Commercial real estate:
Owner occupied	$ 207,060		$ 196,821
Non-owner occupied and other	326,817		328,480
Total commercial real estate loans	533,877		525,301
Construction	48,205		45,650
Residential real estate	95,775		85,494
Commercial and industrial	196,977		162,213
Consumer	37,740		39,506
Total loans, Amount	912,574		858,164
Less:
Deferred loan fees	(1,693)		(1,846)
Reserve for loan losses	(22,694)	(24,548)	(27,261)	(38,219)	(43,951)	(43,905)
Loans, net, Amount	$ 888,187		$ 829,057
Owner occupied, Percent	22.70%		22.90%
Non-owner occupied and other, Percent	35.80%		38.30%
Total commercial real estate loans, Percent	58.50%		61.20%
Construction, Percent	5.30%		5.30%
Residential real estate, Percent	10.50%		10.00%
Commerical and industrial, Percent	21.60%		18.90%
Consumer, Percent	4.10%		4.60%
Total loans, Percent	100.00%		100.00%