Document and Entity Information - shares	6 Months Ended
	Mar. 31, 2018	May 01, 2018
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Trading Symbol	GENC
Entity Registrant Name	GENCOR INDUSTRIES INC
Entity Central Index Key	0000064472
Current Fiscal Year End Date	--09-30
Entity Filer Category	Accelerated Filer
Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		12,196,837
Class B Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		2,288,857