Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 31, 2018
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	2018
Document Fiscal Period Focus	Q2
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Class A [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		9,937,977
Class B [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		19,024,404