Goodwill and Other Intangible Assets (Schedule of Intangible Assets) (Details) - USD ($)	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, accumulated amortization		$ (135,100,000)	$ (120,625,000)
Intangible assets, gross		383,011,399	371,000,000
Intangible assets, net		247,911,399	250,375,000	[1]
Gentex Patents
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		38,011,452	37,328,963
Finite-lived intangible assets, accumulated amortization		(23,982,357)	(22,491,010)
Finite-lived intangible assets, net		14,029,095	14,837,953
Technology Licenses
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		292,943
Finite-lived intangible assets, accumulated amortization		(35,002)
Finite-lived intangible assets, net		257,941
HomeLink® Technology
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		180,000,000	180,000,000
Finite-lived intangible assets, accumulated amortization		(105,000,000)	(93,750,000)
Finite-lived intangible assets, net		$ 75,000,000	86,250,000
Finite-lived intangible asset, useful life	12 years	12 years
Existing Customer Platforms
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		$ 43,000,000	43,000,000
Finite-lived intangible assets, accumulated amortization		(30,100,000)	(26,875,000)
Finite-lived intangible assets, net		$ 12,900,000	16,125,000
Finite-lived intangible asset, useful life	10 years	10 years
Patents and Other Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, accumulated amortization		$ (159,117,359)	(143,116,010)
Intangible assets, gross		421,315,794	408,328,963
Intangible assets, net		262,198,435	265,212,953
HomeLink® Trade Names and Trademarks
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets		52,000,000	52,000,000
Exclusive Licensing Agreement
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets		96,000,000	$ 96,000,000
In-Process R&D | Vaporsens Inc
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets		11,000,000
In-Process R&D | Air-CraftGlass
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets		$ 1,011,399

[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.