Earnings Per Share (Schedule of Earnings Per Share, Basic And Diluted) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerators [Abstract]
Numerator for both basic and diluted EPS, net income	$ 88,535,947	$ 86,485,242	$ 186,092,688	$ 166,765,236
Denominators [Abstract]
Denominator for basic EPS, weighted-average shares outstanding	286,722,482	288,803,045	286,956,367	288,943,030
Potentially dilutive shares resulting from stock plans	3,120,420	2,660,838	3,581,875	2,429,695
Denominator for diluted EPS	289,842,902	291,463,883	290,538,242	291,372,725
Shares related to stock plans not included in diluted average common shares outstanding because their effect would be anti-dilutive	873,937	4,330,316	109,597	6,563,404