Unaudited Condensed Consolidated Statements of Shareholders' Investment - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021		Jun. 30, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	$ 1,960,980,714	$ 1,834,605,633	$ 1,963,943,128	[1]	$ 1,938,087,820
Issuance of common stock from stock plan transactions	4,391,044	8,355,204	$ 13,656,884		15,710,692
Issuance of common stock related to acquisitions		3,559,229			3,559,229
Repurchases of common stock (in shares)			(6,200,000)
Repurchases of common stock	(115,921,079)		$ (213,613,842)		(178,819,584)
Stock-based compensation expense related to stock options, employee stock purchases and restricted stock	6,727,513	5,430,583	12,622,158		11,786,653
Dividends declared	(28,675,992)	(29,493,653)	(57,660,613)		(58,877,512)
Net income (Loss)	86,506,418	(2,374,033)	199,957,288		87,131,768
Other comprehensive (loss) income	2,310,371	2,524,450	(2,586,014)		4,028,347
Balance at end of period	$ 1,916,318,989	$ 1,822,607,413	$ 1,916,318,989		$ 1,822,607,413
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	241,538,824	244,865,658	243,692,869		251,277,515
Balance at beginning of period	$ 14,492,329	$ 14,691,939	$ 14,621,572		$ 15,076,651
Issuance of common stock from stock plan transactions (in shares)	838,896	746,112	1,439,916		1,353,287
Issuance of common stock from stock plan transactions	$ 50,334	$ 44,767	$ 86,395		$ 81,198
Issuance of common stock related to acquisitions (in shares)		163,718			163,718
Issuance of common stock related to acquisitions		$ 9,823			$ 9,823
Repurchases of common stock (in shares)	(3,411,131)		(6,166,196)		(7,019,032)
Repurchases of common stock	$ (204,668)		$ (369,972)		$ (421,143)
Ending balance (in shares)	238,966,589	245,775,488	238,966,589		245,775,488
Balance at end of period	$ 14,337,995	$ 14,746,529	$ 14,337,995		$ 14,746,529
Additional  Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	859,355,232	801,388,454	852,771,508		807,928,139
Issuance of common stock from stock plan transactions	4,340,710	8,310,437	13,570,489		15,629,494
Issuance of common stock related to acquisitions		3,549,406			3,549,406
Repurchases of common stock	(10,745,063)		(19,285,763)		(20,214,812)
Stock-based compensation expense related to stock options, employee stock purchases and restricted stock	6,727,513	5,430,583	12,622,158		11,786,653
Balance at end of period	859,678,392	818,678,880	859,678,392		818,678,880
Retained  Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	1,085,178,486	1,018,310,446	1,089,698,996		1,116,372,133
Repurchases of common stock	(104,971,348)		(193,958,107)		(158,183,629)
Dividends declared	(28,675,992)	(29,493,653)	(57,660,613)		(58,877,512)
Net income (Loss)	86,506,418	(2,374,033)	199,957,288		87,131,768
Balance at end of period	1,038,037,564	986,442,760	1,038,037,564		986,442,760
Accumulated  Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	1,954,667	214,794	6,851,052		(1,289,103)
Other comprehensive (loss) income	2,310,371	2,524,450	(2,586,014)		4,028,347
Balance at end of period	$ 4,265,038	$ 2,739,244	$ 4,265,038		$ 2,739,244

[1] The condensed consolidated balance sheet at December 31, 2020 has been derived from the audited 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.