Goodwill and Other Intangible Assets (Schedule of Intangible Assets) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible assets, net	$ 303,450,000	$ 308,275,000	[1]
Gentex Patents
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	33,620,379	33,002,468
Finite-lived intangible assets, accumulated amortization	(17,147,912)	(16,481,728)
Finite-lived intangible assets, net	16,472,467	16,520,740
Patents and Other Intangible Assets
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, accumulated amortization	(84,697,912)	(79,206,728)
Intangible assets, gross	404,620,379	404,002,468
Intangible assets, net	319,922,467	324,795,740
HomeLink®
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, accumulated amortization	(67,550,000)	(62,725,000)
Intangible assets, gross	371,000,000	371,000,000
Intangible assets, net	303,450,000	308,275,000
HomeLink® | Homelink Technology
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	180,000,000	180,000,000
Finite-lived intangible assets, accumulated amortization	(52,500,000)	(48,750,000)
Finite-lived intangible assets, net	$ 127,500,000	$ 131,250,000
HomeLink® | Homelink Technology | Minimum [Member]
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	12 years	12 years
HomeLink® | Existing Customer Platforms
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 43,000,000	$ 43,000,000
Finite-lived intangible assets, accumulated amortization	(15,050,000)	(13,975,000)
Finite-lived intangible assets, net	$ 27,950,000	$ 29,025,000
Finite-lived intangible asset, useful life	10 years	10 years
HomeLink® | HomeLink Trade Names and Trademarks
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	$ 52,000,000	$ 52,000,000
HomeLink® | Exclusive Licensing Agreement
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	$ 96,000,000	$ 96,000,000

[1] Note: The condensed consolidated balance sheet at December 31, 2016 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.