Earnings Per Share (Schedule Of Earnings Per Share, Basic And Diluted) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share [Abstract]
Numerator for both basic and diluted EPS, net income	$ 43,397,064	$ 34,291,244	$ 124,202,115	$ 100,810,704
Denominator for basic EPS, weighted-average shares outstanding	142,681,780	139,507,360	142,276,965	138,973,832
Potentially dilutive shares resulting from stock plans	1,633,240	1,051,833	1,859,434	1,192,643
Denominator for diluted EPS	144,315,020	140,559,193	144,136,399	140,166,475
Shares related to stock plans not included in diluted average common shares outstanding because their effect would be antidilutive	1,716,832	1,591,642	1,097,397	1,787,200