Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings Per Share (Details) [Abstract]
Number of anti-dilutive stock awards	1,159,842	489,870	1,158,078	484,995
Earnings Per Share (Table Details) [Abstract]
Net earnings	$ 44,182	$ 39,888	$ 96,123	$ 84,118
Basic weighted average shares	59,160,000	62,450,000	59,206,000	62,902,000
Effect of dilutive stock options	418,000	698,000	551,000	818,000
Diluted weighted average shares	59,578,000	63,148,000	59,757,000	63,720,000
Basic earnings per common share	$ 0.75	$ 0.64	$ 1.62	$ 1.34
Diluted earnings per common share	$ 0.74	$ 0.63	$ 1.61	$ 1.32