| Document and Entity Information | Jan. 29, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jan. 29, 2021 |
| Entity Registrant Name | GENTEX CORPORATION |
| Entity Central Index Key | 0000355811 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | MI |
| Entity File Number | 0-10235 |
| Entity Tax Identification Number | 38-2030505 |
| Entity Address, Address Line One | 600 North Centennial Street |
| Entity Address, City or Town | Zeeland |
| Entity Address, State or Province | MI |
| Entity Address, Postal Zip Code | 49464 |
| City Area Code | 616 |
| Local Phone Number | 772-1800 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.06 per share |
| Trading Symbol | GNTX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
