Unaudited Condensed Consolidated Statements of Shareholders' Investment - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020		Jun. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	$ 1,834,605,633	$ 1,857,074,748	$ 1,938,087,820	[1]	$ 1,861,751,660
Issuance of common stock from stock plan transactions	8,355,204	31,420,260	$ 15,710,692		41,934,814
Issuance of common stock related to acquisitions (in shares)			100,000
Issuance of common stock related to acquisitions	3,559,229		$ 3,559,229
Repurchases of common stock (in shares)			(7,000,000.0)
Repurchases of common stock		(69,871,143)	$ (178,819,584)		(166,138,371)
Stock-based compensation expense related to stock options, employee stock purchases and restricted stock	5,430,583	5,276,201	11,786,653		10,139,148
Dividends declared	(29,493,653)	(29,299,410)	(58,877,512)		(58,691,610)
Net (Loss) Income	(2,374,033)	108,958,625	87,131,768		213,239,036
Other comprehensive income	2,524,450	774,955	4,028,347		2,099,558
Balance at end of period	$ 1,822,607,413	$ 1,904,334,236	$ 1,822,607,413		$ 1,904,334,236
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	244,865,658	255,584,345	251,277,515		259,328,613
Balance at beginning of period	$ 14,691,939	$ 15,335,061	$ 15,076,651		$ 15,559,717
Issuance of common stock from stock plan transactions (in shares)	746,112	2,269,483	1,353,287		3,250,153
Issuance of common stock from stock plan transactions	$ 44,767	$ 136,170	$ 81,198		$ 195,010
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)		(3,074,709)	(7,019,032)		(7,799,647)
Repurchases of common stock		$ (184,483)	$ (421,143)		$ (467,979)
Ending balance (in shares)	245,775,488	254,779,119	245,775,488		254,779,119
Balance at end of period	$ 14,746,529	$ 15,286,748	$ 14,746,529		$ 15,286,748
Additional  Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	801,388,454	748,641,461	807,928,139		745,324,144
Issuance of common stock from stock plan transactions	8,310,437	31,284,090	15,629,494		41,739,804
Issuance of common stock related to acquisitions	3,549,406		3,549,406
Repurchases of common stock		(7,963,499)	(20,214,812)		(19,964,843)
Stock-based compensation expense related to stock options, employee stock purchases and restricted stock	5,430,583	5,276,201	11,786,653		10,139,148
Balance at end of period	818,678,880	777,238,253	818,678,880		777,238,253
Retained  Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	1,018,310,446	1,093,373,960	1,116,372,133		1,102,468,137
Repurchases of common stock		(61,723,161)	(158,183,629)		(145,705,549)
Dividends declared	(29,493,653)	(29,299,410)	(58,877,512)		(58,691,610)
Net (Loss) Income	(2,374,033)	108,958,625	87,131,768		213,239,036
Balance at end of period	986,442,760	1,111,310,014	986,442,760		1,111,310,014
Accumulated  Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	214,794	(275,734)	(1,289,103)		(1,600,338)
Other comprehensive income	2,524,450	774,955	4,028,347		2,099,560
Balance at end of period	$ 2,739,244	$ 499,221	$ 2,739,244		$ 499,221

[1] The condensed consolidated balance sheet at December 31, 2019 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.