Consolidated Statements of Financial Position (Parenthetical) (USD $) In Thousands, except Share data	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010
Investment securities:
Held-to-maturity, fair value	$ 185,024	$ 159,188	$ 152,212
Accumulated depreciation of premises and equipment	$ 86,563	$ 80,792	$ 78,767
Shareholders' equity:
Preferred stock, no par value
Preferred stock, shares authorized	200,000	200,000	200,000
Preferred stock, shares issued
Common stock, par value	$ 1	$ 1	$ 1
Common stock, shares authorized	45,000,000	30,000,000	30,000,000
Common stock, shares issued	27,456,907	27,440,006	27,440,006
Common stock, shares outstanding	27,456,907	27,440,006	27,440,006