CONSOLIDATED STATEMENTS OF CONDITION (Unaudited) (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Assets:
Available-for-sale investment securities, cost	$ 2,447,745	$ 2,217,165
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)	75,000,000	75,000,000
Common stock, issued (in shares)	41,464,041	41,213,491
Treasury stock, shares at cost (in shares)	776,091	782,173