Loans and allowance for credit losses (Details 7) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Allowance for credit losses:
Beginning balance	$ 10,725	$ 15,991
Charge-offs	(1,748)	(2,711)
Recoveries	117	305
Net charge-offs	(1,631)	(2,406)
Provision	975	2,150
Ending balance	10,069	15,735
Construction Loans [Member]
Allowance for credit losses:
Beginning balance	1,960	4,387
Charge-offs	(17)	(707)
Recoveries	10	1
Net charge-offs	(7)	(706)
Provision	44	435
Ending balance	1,997	4,116
Residential Real Estate [Member]
Allowance for credit losses:
Beginning balance	3,854	5,194
Charge-offs	(672)	(793)
Recoveries	43	239
Net charge-offs	(629)	(554)
Provision	(1,139)	224
Ending balance	2,086	4,864
Commercial Real Estate [Member]
Allowance for credit losses:
Beginning balance	3,029	4,134
Charge-offs	(90)	(1,075)
Recoveries	6	3
Net charge-offs	(84)	(1,072)
Provision	1,639	1,312
Ending balance	4,584	4,374
Commercial Loan [Member]
Allowance for credit losses:
Beginning balance	1,266	1,682
Charge-offs	(842)	(87)
Recoveries	50	52
Net charge-offs	(792)	(35)
Provision	203	113
Ending balance	677	1,760
Consumer Loan [Member]
Allowance for credit losses:
Beginning balance	243	407
Charge-offs	(127)	(49)
Recoveries	8	10
Net charge-offs	(119)	(39)
Provision	184	(38)
Ending balance	308	330
Unallocated Financing Receivables [Member]
Allowance for credit losses:
Beginning balance	373	187
Charge-offs	0	0
Recoveries	0	0
Net charge-offs	0	0
Provision	44	104
Ending balance	$ 417	$ 291