Loans (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Summary of loans under portfolio
Commercial loan	$ 2,129,234	$ 2,085,325	$ 2,050,361
Consumer loan	1,833,108	1,745,960	1,697,649
Total loans	3,962,342	3,831,285	3,748,010
Commercial [Member]
Summary of loans under portfolio
Commercial loan	915,352	895,150	842,404
Real estate commercial [Member]
Summary of loans under portfolio
Commercial loan	1,119,655	1,071,999	1,065,606
Real estate construction [Member]
Summary of loans under portfolio
Commercial loan	54,538	73,355	91,152
Land development [Member]
Summary of loans under portfolio
Commercial loan	39,689	44,821	51,199
Real estate residential [Member]
Summary of loans under portfolio
Consumer loan	873,214	861,716	825,860
Consumer installment [Member]
Summary of loans under portfolio
Consumer loan	535,283	484,058	517,405
Home equity [Member]
Summary of loans under portfolio
Consumer loan	$ 424,611	$ 400,186	$ 354,384