Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Statement Of Financial Position [Abstract]
Securities available for sale, amortized cost	$ 1,353,442	$ 1,408,780
Held to maturity securities	2,417,879	2,576,584
Property and equipment, accumulated depreciation	$ 178,271	$ 172,798
Common stock, par value per share	$ 3.33	$ 3.33
Common stock, shares authorized	350,000,000	350,000,000
Common stock, shares issued	82,282,057	82,237,162
Common stock, shares outstanding	82,282,057	82,237,162