Consolidated Statements of Condition (Unaudited) (Parenthetical) (USD $) In Thousands, except Share data	Jun. 30, 2011	Dec. 31, 2010
Assets:
Held-to-maturity investment securities, fair value	$ 626,085	$ 625,789
Available-for-sale investment securities, cost	$ 1,401,969	$ 1,076,030
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)	37,619,379	34,131,289
Treasury stock, shares at cost (in shares)	812,346	812,346