CONSOLIDATED STATEMENTS OF CONDITION (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets
Available-for-sale investment securities, cost	$ 1,453,460	$ 1,076,030
Held-to-maturity investment securities, fair value	$ 617,835	$ 625,789
Shareholders' equity
Preferred stock, par value (in dollars per share)	$ 1.00	$ 1.00
Preferred stock, authorized (in shares)	500,000	500,000
Preferred stock, issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00
Common stock, authorized (in shares)	50,000,000	50,000,000
Common stock, issued (in shares)	37,794,532	34,131,289
Treasury stock, shares at cost (in shares)	(808,123)	(812,346)