Consolidated Statements Of Changes In Shareholders' Equity (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Consolidated Statements Of Changes In Shareholders' Equity [Abstract]
Total shareholders' equity at beginning of period	$ 2,283,537	$ 2,061,680
Net income	61,033	51,928
Other comprehensive income (loss)	(3,338)	568
Stock option exercises (108,800 shares in 2012 and 114,293 shares in 2011)	5,542	5,769
Stock compensation expense recognized in earnings	2,555	3,737
Tax benefits (deficiencies) related to stock compensation	(377)	89
Purchase of treasury stock (3,464 shares in 2011)		(201)
Common stock issued/sold to the 401(k) stock purchase plan (22,680 shares in 2011)		1,360
Cash dividends ($0.46 per share in 2012 and $0.45 per share in 2011)	(28,239)	(27,579)
Total shareholders' equity at end of period	$ 2,320,713	$ 2,097,351