Earnings Per Share (Schedule Of Earnings Per Share, Basic And Diluted) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share [Abstract]
Numerator for both basic and diluted EPS, net income	$ 41,877,083	$ 43,397,064	$ 128,988,206	$ 124,202,115
Denominator for basic EPS, weighted-average shares outstanding	143,027,693	142,681,780	143,415,077	142,276,965
Potentially dilutive shares resulting from stock plans	556,682	1,633,240	1,002,142	1,859,434
Denominator for diluted EPS	143,584,375	144,315,020	144,417,219	144,136,399
Shares related to stock plans not included in diluted average common shares outstanding because their effect would be antidilutive	5,332,661	1,716,832	3,289,832	1,097,397