Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity Registrant Name	GAMCO INVESTORS, INC. ET AL
Entity Incorporation, State or Country Code	DE
Entity File Number	001-14761
Entity Tax Identification Number	13-4007862
Entity Address, Address Line One	One Corporate Center
Entity Address, City or Town	Rye
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10580
City Area Code	203
Local Phone Number	629-2726
Entity Filer Category	Accelerated Filer
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Small Business	true
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Central Index Key	0001060349
Title of 12(b) Security	Class A Common Stock, $0.001 par value
Trading Symbol	GBL
Security Exchange Name	NYSE
Class A [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		8,290,951
Class B [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		19,024,117