Loans and reserve for credit losses (Details 5) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Impaired loans, With a related allowance	$ 25,279	$ 27,257
Impaired loans, Without a related allowance	38,010	41,414
Impaired loans,Total recorded balance	63,289	68,671
Impaired loans, Unpaid principal balance	69,171	81,745
Impaired loans, Related allowance	4,429	3,799
Commercial Real Estate Owner Occupied [Member]
Impaired loans, With a related allowance	5,472	8,538
Impaired loans, Without a related allowance	8,965	7,443
Impaired loans,Total recorded balance	14,437	15,981
Impaired loans, Unpaid principal balance	16,970	21,610
Impaired loans, Related allowance	712	988
Commercial Real Estate Non Owner Occupied [Member]
Impaired loans, With a related allowance	4,511	3,712
Impaired loans, Without a related allowance	25,112	23,166
Impaired loans,Total recorded balance	29,623	26,878
Impaired loans, Unpaid principal balance	31,359	32,630
Impaired loans, Related allowance	600	100
Commerical real estate [Member]
Impaired loans, With a related allowance	9,983	12,250
Impaired loans, Without a related allowance	34,077	30,609
Impaired loans,Total recorded balance	44,060	42,859
Impaired loans, Unpaid principal balance	48,329	54,240
Impaired loans, Related allowance	1,312	1,088
Construction [Member]
Impaired loans, With a related allowance	2,418	2,348
Impaired loans, Without a related allowance	875	7,386
Impaired loans,Total recorded balance	3,293	9,734
Impaired loans, Unpaid principal balance	3,323	9,867
Impaired loans, Related allowance	416	440
Residential real estate [Member]
Impaired loans, With a related allowance	4,539	4,530
Impaired loans, Without a related allowance	294	310
Impaired loans,Total recorded balance	4,833	4,840
Impaired loans, Unpaid principal balance	5,021	5,018
Impaired loans, Related allowance	1,141	1,141
Commercial and industrial loans [Member]
Impaired loans, With a related allowance	6,401	6,493
Impaired loans, Without a related allowance	2,764	3,109
Impaired loans,Total recorded balance	9,165	9,602
Impaired loans, Unpaid principal balance	10,560	10,982
Impaired loans, Related allowance	1,230	829
Consumer Loans [Member]
Impaired loans, With a related allowance	1,938	1,636
Impaired loans, Without a related allowance	0	0
Impaired loans,Total recorded balance	1,938	1,636
Impaired loans, Unpaid principal balance	1,938	1,638
Impaired loans, Related allowance	$ 330	$ 301