CONSOLIDATED STATEMENTS OF CONDITION (Unaudited) (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Assets:
Available-for-sale investment securities, cost	$ 2,076,249	$ 1,453,461
Held-to-maturity investment securities, fair value	$ 717,179	$ 617,835
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)	40,273,189	37,794,532
Treasury stock, shares at cost (in shares)	801,260	808,123