Earnings Per Share (Schedule of Earnings Per Share, Basic And Diluted) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerators [Abstract]
Numerator for both basic and diluted EPS, net income	$ 90,230,335	$ 92,064,646	$ 276,323,023	$ 258,829,882
Denominators [Abstract]
Denominator for basic EPS, weighted-average shares outstanding	284,661,920	287,736,638	285,915,565	288,466,905
Potentially dilutive shares resulting from stock plans	2,359,030	2,717,187	3,145,936	2,557,758
Denominator for diluted EPS	287,020,950	290,453,825	289,061,501	291,024,663
Shares related to stock plans not included in diluted average common shares outstanding because their effect would be anti-dilutive	807,013	1,818,032	2,847,247	4,193,947