Earnings Per Share (Details) (USD $) In Thousands, except Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Earnings Per Share (Details) [Abstract]
Number of anti-dilutive stock options	489,870	1,933,176	484,995	2,198,971
Earnings Per Share (Table Details) [Abstract]
Net earnings	$ 39,888	$ 47,830	$ 84,118	$ 99,291
Basic weighted average shares	62,450,000	65,945,000	62,902,000	65,822,000
Effect of dilutive stock options	698,000	828,000	818,000	823,000
Diluted weighted average shares	63,148,000	66,773,000	63,720,000	66,645,000
Basic earnings per common share	$ 0.64	$ 0.73	$ 1.34	$ 1.51
Diluted earnings per common share	$ 0.63	$ 0.72	$ 1.32	$ 1.49