Goodwill and Other Intangible Assets (Schedule of Intangible Assets) (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible assets, net	$ 337,225,000	$ 346,875,000	[1]
Gentex Patents
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	30,528,992	30,132,116
Finite-lived intangible assets, accumulated amortization	(12,396,365)	(11,065,153)
Finite-lived intangible assets, net	18,132,627	19,066,963
Patents and Other Intangible Assets [Member]
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, accumulated amortization	(46,171,365)	(35,190,153)
Intangible assets, gross	401,528,992	401,132,116
Intangible assets, net	355,357,627	365,941,963
HomeLink®
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, accumulated amortization	(33,775,000)	(24,125,000)
Intangible assets, gross	371,000,000	371,000,000
Intangible assets, net	337,225,000	346,875,000
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	(26,250,000)	(18,750,000)
Finite-lived intangible assets, net	$ 153,750,000	$ 161,250,000
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	(7,525,000)	(5,375,000)
Finite-lived intangible assets, net	$ 35,475,000	$ 37,625,000
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, 2014 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.