Earnings Per Share (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Earnings Per Share, Basic and Diluted
Net earnings	$ 69,478	$ 83,380	$ 116,468	$ 154,734
Less: net earnings attributable to unvested restricted stock and restricted stock units	(1,003)	(927)	(1,601)	(1,679)
Net earnings available to common stock	$ 68,475	$ 82,453	$ 114,867	$ 153,055
Weighted-average common shares outstanding	111,389	113,935	112,569	113,805
Dilutive effect of outstanding options (determined using treasury stock method)	368	253	375	322
Weighted-average common shares and potential common shares outstanding	111,757	114,188	112,944	114,127
Anti-dilutive stock options not included in treasury stock method computation	424	4,680	917	4,392