Loans and allowance for credit losses (Details 7) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Allowance for credit losses:
Beginning balance	$ 10,069	$ 15,735	$ 10,725	$ 15,991
Charge-offs	(2,177)	(2,919)	(3,925)	(5,630)
Recoveries	234	207	351	512
Net charge-offs	(1,943)	(2,712)	(3,574)	(5,118)
Provision	950	2,700	1,925	4,850
Ending balance	9,076	15,723	9,076	15,723
Construction Loans [Member]
Allowance for credit losses:
Beginning balance	1,997	4,116	1,960	4,387
Charge-offs	(224)	(802)	(241)	(1,509)
Recoveries	1	1	11	2
Net charge-offs	(223)	(801)	(230)	(1,507)
Provision	474	1,031	518	1,466
Ending balance	2,248	4,346	2,248	4,346
Residential Real Estate [Member]
Allowance for credit losses:
Beginning balance	2,086	4,864	3,854	5,194
Charge-offs	(315)	(1,096)	(987)	(1,889)
Recoveries	63	59	106	298
Net charge-offs	(252)	(1,037)	(881)	(1,591)
Provision	520	432	(619)	656
Ending balance	2,354	4,259	2,354	4,259
Commercial Real Estate [Member]
Allowance for credit losses:
Beginning balance	4,584	4,374	3,029	4,134
Charge-offs	(1,523)	(872)	(1,613)	(1,947)
Recoveries	7	90	13	93
Net charge-offs	(1,516)	(782)	(1,600)	(1,854)
Provision	(416)	1,922	1,223	3,234
Ending balance	2,652	5,514	2,652	5,514
Commercial Loan [Member]
Allowance for credit losses:
Beginning balance	677	1,760	1,266	1,682
Charge-offs	(95)	(136)	(937)	(223)
Recoveries	157	50	207	102
Net charge-offs	62	(86)	(730)	(121)
Provision	119	(458)	322	(345)
Ending balance	858	1,216	858	1,216
Consumer Loan [Member]
Allowance for credit losses:
Beginning balance	308	330	243	407
Charge-offs	(20)	(13)	(147)	(62)
Recoveries	6	7	14	17
Net charge-offs	(14)	(6)	(133)	(45)
Provision	12	(23)	196	(61)
Ending balance	306	301	306	301
Unallocated Financing Receivables [Member]
Allowance for credit losses:
Beginning balance	417	291	373	187
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Net charge-offs	0	0	0	0
Provision	241	(204)	285	(100)
Ending balance	$ 658	$ 87	$ 658	$ 87