Cover Page - shares	3 Months Ended
	Dec. 31, 2019	Jan. 30, 2020
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Entity Registrant Name	GENCOR INDUSTRIES INC
Trading Symbol	GENC
Entity Central Index Key	0000064472
Current Fiscal Year End Date	--09-30
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Interactive Data Current	Yes
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Title of 12(b) Security	Common Stock
Security Exchange Name	NASDAQ
Entity Address, State or Province	FL
Entity Incorporation, State or Country Code	DE
Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		12,277,337
Class B Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		2,308,857