Consolidated Statements of Financial Position (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Consolidated Statements of Financial Position [Abstract]
Held-to-maturity, fair value	$ 213,852	$ 183,769	$ 187,595
Accumulated depreciation of premises and equipment	$ 89,261	$ 86,991	$ 84,731
Preferred stock, no par value
Preferred stock, shares authorized	200,000	200,000	200,000
Preferred stock, shares issued	0	0	0
Common stock, par value	$ 1	$ 1	$ 1
Common stock, shares authorized	45,000,000	45,000,000	45,000,000
Common stock, shares issued	27,497,442	27,456,907	27,456,907
Common stock, shares outstanding	27,497,442	27,456,907	27,456,907