Goodwill and Other Intangible Assets (Schedule of Intangible Assets) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, accumulated amortization	$ (144,750,000)	$ (139,925,000)
Intangible assets, gross	401,661,809	389,673,127
Intangible assets, net	256,911,809	249,748,127	[1]
Gentex Patents
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	38,906,267	38,625,292
Finite-lived intangible assets, accumulated amortization	(25,116,962)	(24,528,853)
Finite-lived intangible assets, net	13,789,305	14,096,439
Vaporsens Technology Licenses
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	315,425	300,985
Finite-lived intangible assets, accumulated amortization	(54,062)	(38,856)
Finite-lived intangible assets, net	261,363	262,129
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	(112,500,000)	(108,750,000)
Finite-lived intangible assets, net	$ 67,500,000	$ 71,250,000
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	(32,250,000)	(31,175,000)
Finite-lived intangible assets, net	$ 10,750,000	$ 11,825,000
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	$ (169,921,024)	$ (164,453,853)
Intangible assets, gross	440,883,501	428,298,419
Intangible assets, net	270,962,477	263,844,566
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	11,000,000
In-Process R&D | Argil, Inc.
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	6,278,132	6,278,132
In-Process R&D | Air-CraftGlass
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	1,389,237	$ 1,394,995
In-Process R&D | Guardian Optical Technologies
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	$ 11,994,440

[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.