Unaudited Condensed Consolidated Statements of Shareholders' Investment - USD ($)	3 Months Ended
	Mar. 31, 2022		Mar. 31, 2021
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	$ 1,937,988,467	[1]	$ 1,963,943,128
Issuance of common stock from stock plan transactions	$ 3,324,147		9,265,840
Repurchases of common stock (in shares)	(2,400,000)
Repurchases of common stock	$ (71,252,022)		(97,692,763)
Stock-based compensation expense related to stock options, employee stock purchases and restricted stock	6,788,337		5,894,645
Dividends declared ($0.12 per share)	(28,354,003)		(28,984,621)
Net income	87,528,626		113,450,870
Other comprehensive loss	(7,054,652)		(4,896,385)
Balance at end of period	$ 1,928,968,900		$ 1,960,980,714
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	236,440,840		243,692,869
Balance at beginning of period	$ 14,186,450		$ 14,621,572
Issuance of common stock from stock plan transactions (in shares)	476,688		601,020
Issuance of common stock from stock plan transactions	$ 28,601		$ 36,061
Repurchases of common stock (in shares)	(2,440,190)		(2,755,065)
Repurchases of common stock	$ (146,411)		$ (165,304)
Ending balance (in shares)	234,477,338		241,538,824
Balance at end of period	$ 14,068,640		$ 14,492,329
Additional  Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	879,413,385		852,771,508
Issuance of common stock from stock plan transactions	3,295,546		9,229,779
Repurchases of common stock	(8,125,830)		(8,540,700)
Stock-based compensation expense related to stock options, employee stock purchases and restricted stock	6,788,337		5,894,645
Balance at end of period	881,371,438		859,355,232
Retained  Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	1,042,461,388		1,089,698,996
Repurchases of common stock	(62,979,781)		(88,986,759)
Dividends declared ($0.12 per share)	(28,354,003)		(28,984,621)
Net income	87,528,626		113,450,870
Balance at end of period	1,038,656,230		1,085,178,486
Accumulated  Other Comprehensive (Loss) Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	1,927,244		6,851,052
Other comprehensive loss	(7,054,652)		(4,896,385)
Balance at end of period	$ (5,127,408)		$ 1,954,667

[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.