Shareholders' Equity (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended				6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 Common Stock [Member]	Dec. 31, 2010 Common Stock [Member]	Jun. 30, 2011 Additional Paid-in Capital [Member]	Jun. 30, 2011 Retained Earnings [Member]	Jun. 30, 2011 Treasury Stock [Member]	Jun. 30, 2011 Deferred Compensation Trust [Member]	Jun. 30, 2011 Deferred Compensation Liability [Member]
Summary of changes in shareholders' equity
Balance, December 31, 2010			$ 1,740,374		$ 206	$ 206	$ 951,234	$ 4,029,072	$ (3,240,138)	$ (27,582)	$ 27,582
Net income	38,445	71,276	53,619	103,363				53,619
Deferred compensation activity										2,000	(2,000)
Purchase of common stock for treasury			(300,885)						(300,885)
Equity-based compensation			31,705				31,705
Tax benefit from stock options exercised and deferred compensation distributions			21,391				21,391
Proceeds from stock options exercised			104,592	51,537			104,592
Treasury stock issued upon option exercise							(71,623)		71,623
Balance, June 30, 2011	1,650,796		1,650,796		206	206	1,037,299	4,082,691	(3,469,400)	(25,582)	25,582
Shareholders' Equity (Textuals) [Abstract]
Common stock repurchased			411,477
Aggregate purchase price of common stock			$ 300,885						$ 300,885
Stock option exercised			329,000