Shareholders' Equity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended				6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Common Stock [Member]	Dec. 31, 2011 Common Stock [Member]	Jun. 30, 2012 Additional Paid-In Capital [Member]	Jun. 30, 2012 Retained Earnings [Member]	Jun. 30, 2012 Treasury Stock [Member]	Jun. 30, 2012 Deferred Compensation Trust [Member]	Jun. 30, 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	46,838	38,445	66,961	53,619				66,961
Deferred compensation activity										250	(250)
Equity-based compensation			33,173				33,173
Tax benefit from equity benefit plan activity			4,709				4,709
Proceeds from stock options exercised			42,182				42,182
Treasury stock issued upon option exercise and restricted share vesting							(39,725)		39,725
Balance, June 30, 2012	$ 1,521,824		$ 1,521,824		$ 206	$ 206	$ 1,113,118	$ 4,225,453	$ (3,816,953)	$ (25,331)	$ 25,331