v3.8.0.1
Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2017
Feb. 01, 2018
Jun. 30, 2017
Document And Entity Information [Abstract]      
Entity Registrant Name GENTEX CORP    
Entity Central Index Key 0000355811    
Current Fiscal Year End Date --12-31    
Entity Filer Category Large Accelerated Filer    
Document Type 10-K    
Document Period End Date Dec. 31, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY    
Amendment Flag false    
Entity Common Stock, Shares Outstanding   274,421,032  
Entity Public Float     $ 5,284,326,964
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Well-known Seasoned Issuer Yes