Unaudited Condensed Consolidated Statements of Shareholders' Investment - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021		Sep. 30, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	$ 1,916,318,989	$ 1,822,607,413	$ 1,963,943,128	[1]	$ 1,938,087,820
Issuance of common stock from stock plan transactions	7,116,990	7,966,489	$ 20,773,874		23,677,181
Issuance of common stock related to acquisitions					3,559,229
Repurchases of common stock (in shares)			(9,000,000)
Repurchases of common stock	(90,581,913)	(31,660,862)	$ (304,195,755)		(210,480,446)
Stock-based compensation expense related to stock options, employee stock purchases and restricted stock	7,492,763	7,306,543	20,114,921		19,093,196
Dividends declared	(28,382,653)	(29,407,702)	(86,043,266)		(88,285,214)
Net income	76,660,548	117,092,602	276,617,836		204,224,370
Other comprehensive (loss) income	(994,438)	1,707,816	(3,580,452)		5,736,163
Balance at end of period	$ 1,887,630,286	$ 1,895,612,299	$ 1,887,630,286		$ 1,895,612,299
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	238,966,589	245,775,488	243,692,869		251,277,515
Balance at beginning of period	$ 14,337,995	$ 14,746,529	$ 14,621,572		$ 15,076,651
Issuance of common stock from stock plan transactions (in shares)	398,873	461,983	1,838,789		1,815,270
Issuance of common stock from stock plan transactions	$ 23,932	$ 27,719	$ 110,327		$ 108,917
Issuance of common stock related to acquisitions (in shares)					163,718
Issuance of common stock related to acquisitions					$ 9,823
Repurchases of common stock (in shares)	(2,830,850)	(1,175,756)	(8,997,046)		(8,194,788)
Repurchases of common stock	$ (169,851)	$ (70,545)	$ (539,823)		$ (491,688)
Ending balance (in shares)	236,534,612	245,061,715	236,534,612		245,061,715
Balance at end of period	$ 14,192,076	$ 14,703,703	$ 14,192,076		$ 14,703,703
Additional  Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	859,678,392	818,678,880	852,771,508		807,928,139
Issuance of common stock from stock plan transactions	7,093,058	7,938,770	20,663,547		23,568,264
Issuance of common stock related to acquisitions					3,549,406
Repurchases of common stock	(9,200,264)	(3,515,510)	(28,486,027)		(23,730,322)
Stock-based compensation expense related to stock options, employee stock purchases and restricted stock	7,492,763	7,306,543	20,114,921		19,093,196
Balance at end of period	865,063,949	830,408,683	865,063,949		830,408,683
Retained  Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	1,038,037,564	986,442,760	1,089,698,996		1,116,372,133
Repurchases of common stock	(81,211,798)	(28,074,807)	(275,169,905)		(186,258,436)
Dividends declared	(28,382,653)	(29,407,702)	(86,043,266)		(88,285,214)
Net income	76,660,548	117,092,602	276,617,836		204,224,370
Balance at end of period	1,005,103,661	1,046,052,853	1,005,103,661		1,046,052,853
Accumulated  Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	4,265,038	2,739,244	6,851,052		(1,289,103)
Other comprehensive (loss) income	(994,438)	1,707,816	(3,580,452)		5,736,163
Balance at end of period	$ 3,270,600	$ 4,447,060	$ 3,270,600		$ 4,447,060

[1] The condensed consolidated balance sheet at December 31, 2020 has been derived from the audited consolidated financial statements at that date but does not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements.