Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Statement Of Financial Position [Abstract]
Interest bearing deposits, banks	$ 12,698	$ 15,550
Held-to-maturity securities, fair values	$ 628,540	$ 596,308
Preferred stock, no par value
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	29,367,511	29,367,511
Common stock, shares outstanding	29,278,925	29,175,236
Treasury stock, shares	88,586	192,275