Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets
Held-to-maturity securities, fair value	$ 0	$ 1,632,691
Available-for-sale securities, amortized cost	$ 2,448,051	$ 1,074,350
Shareholders' Equity
Common stock, par value	$ 2.50	$ 2.50
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	83,483,796	83,481,737