CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Statement Of Financial Position [Abstract]
Held to maturity, market value	$ 142,531	$ 129,495
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares authorized	80,000,000	80,000,000
Common stock, shares issued	55,056,730	55,056,730
Common stock, shares outstanding	40,520,464	40,340,878
Treasury stock, shares	14,536,266	14,715,852