Unaudited Condensed Consolidated Statements of Shareholders' Investment - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022		Jun. 30, 2021
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	$ 1,928,968,900	$ 1,960,980,714	$ 1,937,988,467	[1]	$ 1,963,943,128
Issuance of common stock from stock plan transactions	5,671,020	4,391,044	8,995,167		13,656,884
Issuance of common stock for equity investment purchases	5,000,012		$ 5,000,012
Repurchases of common stock (in shares)			(2,400,000)
Repurchases of common stock		(115,921,079)	$ (71,252,022)		(213,613,842)
Stock-based compensation expense related to stock options, employee stock purchases and restricted stock	8,573,230	6,727,513	15,361,567		12,622,158
Dividends declared ($0.24 per share)	(28,214,614)	(28,675,992)	(56,568,616)		(57,660,613)
Net income	72,404,403	86,506,418	159,933,028		199,957,288
Other comprehensive income (loss)	(5,828,471)	2,310,371	(12,883,123)		(2,586,014)
Balance at end of period	$ 1,986,574,480	$ 1,916,318,989	$ 1,986,574,480		$ 1,916,318,989
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	234,477,338	241,538,824	236,440,840		243,692,869
Balance at beginning of period	$ 14,068,640	$ 14,492,329	$ 14,186,450		$ 14,621,572
Issuance of common stock from stock plan transactions (in shares)	492,494	838,896	969,182		1,439,916
Issuance of common stock from stock plan transactions	$ 29,550	$ 50,334	$ 58,151		$ 86,395
Issuance of common stock for equity investment purchases (in shares)	162,433		162,433
Issuance of common stock for equity investment purchases	$ 9,746		$ 9,746
Repurchases of common stock (in shares)		(3,411,131)	(2,440,190)		(6,166,196)
Repurchases of common stock		$ (204,668)	$ (146,411)		$ (369,972)
Ending balance (in shares)	235,132,265	238,966,589	235,132,265		238,966,589
Balance at end of period	$ 14,107,936	$ 14,337,995	$ 14,107,936		$ 14,337,995
Additional  Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	881,371,438	859,355,232	879,413,385		852,771,508
Issuance of common stock from stock plan transactions	5,641,470	4,340,710	8,937,016		13,570,489
Issuance of common stock for equity investment purchases	4,990,266		4,990,266
Repurchases of common stock		(10,745,063)	(8,125,830)		(19,285,763)
Stock-based compensation expense related to stock options, employee stock purchases and restricted stock	8,573,230	6,727,513	15,361,567		12,622,158
Balance at end of period	900,576,404	859,678,392	900,576,404		859,678,392
Retained  Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	1,038,656,230	1,085,178,486	1,042,461,388		1,089,698,996
Repurchases of common stock		(104,971,348)	(62,979,781)		(193,958,107)
Dividends declared ($0.24 per share)	(28,214,614)	(28,675,992)	(56,568,616)		(57,660,613)
Net income	72,404,403	86,506,418	159,933,028		199,957,288
Balance at end of period	1,082,846,019	1,038,037,564	1,082,846,019		1,038,037,564
Accumulated  Other Comprehensive (Loss) Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	(5,127,408)	1,954,667	1,927,244		6,851,052
Other comprehensive income (loss)	(5,828,471)	2,310,371	(12,883,123)		(2,586,014)
Balance at end of period	$ (10,955,879)	$ 4,265,038	$ (10,955,879)		$ 4,265,038

[1] The condensed consolidated balance sheet at December 31, 2021 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.