Loans (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Summary of loans under portfolio
Commercial loan	$ 2,159,893	$ 2,085,325	$ 2,034,890
Consumer loan	1,859,266	1,745,960	1,725,536
Total loans	4,019,159	3,831,285	3,760,426
Commercial [Member]
Summary of loans under portfolio
Commercial loan	951,938	895,150	858,969
Real estate commercial [Member]
Summary of loans under portfolio
Commercial loan	1,117,073	1,071,999	1,056,092
Real estate construction [Member]
Summary of loans under portfolio
Commercial loan	56,071	73,355	72,851
Land development [Member]
Summary of loans under portfolio
Commercial loan	34,811	44,821	46,978
Real estate residential [Member]
Summary of loans under portfolio
Consumer loan	880,295	861,716	840,044
Consumer installment [Member]
Summary of loans under portfolio
Consumer loan	538,412	484,058	526,573
Home equity [Member]
Summary of loans under portfolio
Consumer loan	$ 440,559	$ 400,186	$ 358,919