Shareholders' Equity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 Common Stock [Member]	Dec. 31, 2011 Common Stock [Member]	Mar. 31, 2012 Additional Paid In Capital [Member]	Mar. 31, 2012 Retained Earnings [Member]	Mar. 31, 2012 Treasury Stock [Member]	Mar. 31, 2012 Deferred Compensation Trust [Member]	Mar. 31, 2012 Deferred Compensation Liability [Member]
Summary of changes in shareholders equity
Balance, December 31, 2011	$ 1,374,799		$ 206	$ 206	$ 1,072,779	$ 4,158,492	$ (3,856,678)	$ (25,581)	$ 25,581
Net income	20,123	15,174				20,123
Deferred compensation activity								250	(250)
Equity-based compensation	16,440				16,440
Tax benefit from equity benefit plan activity	876				876
Proceeds from stock options exercised	6,003				6,003
Treasury stock issued upon option exercise					(21,883)		21,883
Balance, March 31, 2012	$ 1,418,241		$ 206	$ 206	$ 1,074,215	$ 4,178,615	$ (3,834,795)	$ (25,331)	$ 25,331