Document And Entity Information - shares
9 Months Ended
Sep. 30, 2016
Oct. 20, 2016
Document And Entity Information [Abstract]    
Entity Registrant Name GENTEX CORPORATION  
Entity Central Index Key 0000355811  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Document Type 10-Q  
Document Period End Date Sep. 30, 2016  
Document Fiscal Year Focus 2016  
Document Fiscal Period Focus Q3  
Amendment Flag false  
Trading Symbol gntx  
Entity Common Stock, Shares Outstanding   286,509,623