Earnings Per Share (Schedule Of Earnings Per Share, Basic And Diluted) (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share [Abstract]
Numerator for both basic and diluted EPS, net income	$ 45,430,567	$ 46,344,584
Denominator for basic EPS, weighted-average shares outstanding (in shares)	142,534,655	143,502,772
Potentially dilutive shares resulting from stock plans (in shares)	540,810	1,485,229
Denominator for diluted EPS (in shares)	143,075,465	144,988,001
Shares related to stock plans not included in diluted average common shares outstanding because their effect would be antidilutive (in shares)	5,034,165	2,233,907