Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2020	Apr. 30, 2020
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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Entity Address, State or Province	NY
Class A [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		8,666,148
Class B [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		19,024,117