Loans (Summary of Loans) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Summary of loans under portfolio
Commercial loan	$ 2,298,505	$ 2,264,820	$ 2,100,885
Consumer loan	1,886,756	1,902,915	1,742,213
Total loans	4,185,261	4,167,735	3,843,098
Commercial [Member]
Summary of loans under portfolio
Commercial loan	1,038,115	1,002,722	903,935
Real estate commercial [Member]
Summary of loans under portfolio
Commercial loan	1,162,383	1,161,861	1,095,793
Real estate construction [Member]
Summary of loans under portfolio
Commercial loan	65,367	62,689	56,906
Land development [Member]
Summary of loans under portfolio
Commercial loan	32,640	37,548	44,251
Real estate residential [Member]
Summary of loans under portfolio
Consumer loan	872,454	883,835	861,301
Consumer installment [Member]
Summary of loans under portfolio
Consumer loan	540,216	546,036	480,622
Home equity [Member]
Summary of loans under portfolio
Consumer loan	$ 474,086	$ 473,044	$ 400,290