Document and Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2017	Dec. 01, 2017	Mar. 31, 2017
Document Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Trading Symbol	GENC
Entity Registrant Name	GENCOR INDUSTRIES INC
Entity Central Index Key	0000064472
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 152,357,700
Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		12,154,829
Class B Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		2,263,857