Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Statement Of Financial Position [Abstract]
Securities available for sale, amortized cost	$ 1,435,823	$ 1,986,882
Held to maturity securities	2,653,867	1,710,465
Property and equipment, accumulated depreciation	$ 169,178	$ 160,592
Common stock, par value per share	$ 3.33	$ 3.33
Common stock, shares authorized	350,000,000	350,000,000
Common stock, shares issued	82,106,957	84,847,796
Common stock, shares outstanding	82,106,957	84,847,796