Earnings Per Share (Schedule Of Earnings Per Share, Basic And Diluted) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerators [Abstract]
Numerator for both basic and diluted EPS, net income	$ 55,520,961	$ 41,877,083	$ 153,048,925	$ 128,988,206
Denominators [Abstract]
Denominator for basic EPS, weighted-average shares outstanding	143,697,760	143,027,693	143,160,402	143,415,077
Potentially dilutive shares resulting from stock plans	821,140	556,682	655,639	1,002,142
Denominator for diluted EPS	144,518,900	143,584,375	143,816,041	144,417,219
Shares related to stock plans not included in diluted average common shares outstanding because their effect would be anti-dilutive	3,220,980	5,332,661	3,573,418	3,289,832