Document and Entity Information	9 Months Ended
	Sep. 30, 2018 shares
Entity Information [Line Items]
Entity Registrant Name	GAMCO INVESTORS, INC. ET AL
Entity Central Index Key	0001060349
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Ex Transition Period	false
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Class A [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding	10,040,776
Class B [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding	19,024,404