Loans and reserve for credit losses (Details 5) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Impaired loans with specific valuation allowances	$ 17,574	$ 27,257
Impaired loans, Without a related allowance	34,158	41,414
Impaired loans,Total recorded balance	51,732	68,671
Impaired loans, Unpaid principal balance	56,955	81,745
Impaired loans, Related allowance	2,661	3,799
Commercial Real Estate Owner Occupied [Member]
Impaired loans with specific valuation allowances	10,006	8,538
Impaired loans, Without a related allowance	5,916	7,443
Impaired loans,Total recorded balance	15,922	15,981
Impaired loans, Unpaid principal balance	18,671	21,610
Impaired loans, Related allowance	1,936	988
Commercial Real Estate Non Owner Occupied [Member]
Impaired loans with specific valuation allowances	1,933	3,712
Impaired loans, Without a related allowance	24,623	23,166
Impaired loans,Total recorded balance	26,556	26,878
Impaired loans, Unpaid principal balance	26,906	32,630
Impaired loans, Related allowance	216	100
Commerical real estate [Member]
Impaired loans with specific valuation allowances	11,939	12,250
Impaired loans, Without a related allowance	30,539	30,609
Impaired loans,Total recorded balance	42,478	42,859
Impaired loans, Unpaid principal balance	45,577	54,240
Impaired loans, Related allowance	2,152	1,088
Construction [Member]
Impaired loans with specific valuation allowances	796	2,348
Impaired loans, Without a related allowance	868	7,386
Impaired loans,Total recorded balance	1,664	9,734
Impaired loans, Unpaid principal balance	1,833	9,867
Impaired loans, Related allowance	5	440
Residential real estate [Member]
Impaired loans with specific valuation allowances	378	4,530
Impaired loans, Without a related allowance	291	310
Impaired loans,Total recorded balance	669	4,840
Impaired loans, Unpaid principal balance	750	5,018
Impaired loans, Related allowance	173	1,141
Commercial and industrial loans [Member]
Impaired loans with specific valuation allowances	4,461	6,493
Impaired loans, Without a related allowance	2,460	3,109
Impaired loans,Total recorded balance	6,921	9,602
Impaired loans, Unpaid principal balance	8,795	10,982
Impaired loans, Related allowance	331	829
Consumer Loans [Member]
Impaired loans with specific valuation allowances	0	1,636
Impaired loans, Without a related allowance	0	0
Impaired loans,Total recorded balance	0	1,636
Impaired loans, Unpaid principal balance	0	1,638
Impaired loans, Related allowance	$ 0	$ 301