Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Statement Of Financial Position [Abstract]
Fair value of held-to-maturity investment securities	$ 70,079	$ 71,327	[1]
Accumulated amortization and fair value adjustments on other intangibles	$ 9,783	$ 10,475	[1]
Common stock, par value	$ 5	$ 5	[1]
Common stock, shares authorized	48,000,000	48,000,000	[1]
Common stock, shares issued	18,266,404	18,266,404	[1]
Common stock, shares outstanding	16,288,597	16,770,232	[1]
Treasury stock, shares	1,977,807	1,496,172	[1]

[1] Note: The consolidated balance sheet at December 31, 2012 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by U. S. generally accepted accounting principles for complete financial statements. See accompanying notes to the unaudited consolidated financial statements.