Earnings Per Share (Schedule Of Earnings Per Share, Basic And Diluted) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerators [Abstract]
Numerator for both basic and diluted EPS, net income	$ 52,097,397	$ 40,766,539	$ 97,527,964	$ 87,111,123
Denominators [Abstract]
Denominator for basic EPS, weighted-average shares outstanding	143,240,333	143,722,329	142,888,337	143,610,898
Potentially dilutive shares resulting from stock plans	770,292	1,019,028	649,655	1,243,334
Denominator for diluted EPS	144,010,625	144,741,357	143,537,992	144,854,232
Shares related to stock plans not included in diluted average common shares outstanding because their effect would be anti-dilutive	3,270,342	3,513,682	3,454,067	2,906,932