Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Consolidated Balance Sheets [Abstract]
Marketable equity securities, amortized cost	$ 719,556	$ 752,085
Securities held to maturity	$ 56,348	$ 56,181
Preferred stock, par value	$ 1.00	$ 1.00
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued
Common stock, par value	$ 2.50	$ 2.50
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	50,867,630	50,867,630
Common stock, shares in treasury	593,526	654,682