Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	Apr. 30, 2019
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	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Class A [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		8,586,327
Class B [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		19,024,117