Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Marketable equity securities, amortized cost	$ 664,042	$ 752,085
Securities held to maturity	$ 51,494	$ 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	591,761	654,682