Earnings Per Share (Schedule of Earnings Per Share, Basic And Diluted) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerators [Abstract]
Numerator for both basic and diluted EPS, net income	$ 86,485,242	$ 74,558,437	$ 166,765,236	$ 151,741,878
Denominators [Abstract]
Denominator for basic EPS, weighted-average shares outstanding	288,803,045	293,958,258	288,943,030	294,461,499
Potentially dilutive shares resulting from stock plans	2,660,838	3,503,844	2,429,695	3,528,533
Denominator for diluted EPS	291,463,883	297,462,102	291,372,725	297,990,032
Shares related to stock plans not included in diluted average common shares outstanding because their effect would be anti-dilutive	4,330,316	1,804,157	6,563,404	1,496,107