Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 01, 2020	Jun. 30, 2019
Cover page.
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	000-10235
Entity Registrant Name	GENTEX CORPORATION
Entity Incorporation, State or Country Code	MI
Entity Tax Identification Number	38-2030505
Entity Address, Address Line One	600 N. Centennial Street,
Entity Address, State or Province	MI
Entity Address, Postal Zip Code	49464
Entity Address, City or Town	Zeeland,
City Area Code	616
Local Phone Number	772-1800
Title of 12(b) Security	Common Stock, par value $.06 per share
Trading Symbol	GNTX
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Public Float			$ 6,258,471,128
Entity Common Stock, Shares Outstanding		251,274,340
Entity Filer Category	Large Accelerated Filer
Entity Central Index Key	0000355811
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Amendment Flag	false