Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Statement Of Financial Position [Abstract]
Interest bearing deposits, banks	$ 8,425	$ 33,889
Held-to-maturity securities, fair values	$ 615,203	$ 639,273
Preferred stock, par value	$ 0	$ 0
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 2.0833	$ 2.0833
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	29,282,412	29,214,660
Common stock, shares outstanding	29,282,412	29,214,660
Treasury stock, shares	0	0