Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 31, 2017
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 Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Class A [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		10,089,844
Class B [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		19,062,168