Consolidated Statements of Financial Position (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Consolidated Statements of Financial Position [Abstract]
Held-to-maturity, fair value	$ 192,372	$ 183,769	$ 158,312
Accumulated depreciation of premises and equipment	$ 88,603	$ 86,991	$ 82,676
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	45,000,000	30,000,000
Common stock, shares issued	27,491,026	27,456,907	27,451,367
Common stock, shares outstanding	27,491,026	27,456,907	27,451,367