Document and Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2021
Feb. 28, 2022
Jun. 30, 2021
Entity Information [Line Items]      
Document Type 10-K    
Amendment Flag false    
Document Annual Report true    
Document Period End Date Dec. 31, 2021    
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2021    
Document Fiscal Period Focus FY    
Document Transition Report false    
Entity File Number 001-14761    
Entity Registrant Name GAMCO INVESTORS, INC. ET AL    
Entity Central Index Key 0001060349    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 13-4007862    
Entity Address, Address Line One 191 Mason Street    
Entity Address, City or Town Greenwich    
Entity Address, State or Province CT    
Entity Address, Postal Zip Code 06830    
City Area Code 203    
Local Phone Number 629-2726    
Title of 12(b) Security Class A Common Stock, $0.001 par value    
Trading Symbol GBL    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 137,117,912
ICFR Auditor Attestation Flag true    
Auditor Name Deloitte & Touche, LLP    
Auditor Location Stamford, Connecticut    
Auditor Firm ID 34    
Class A [Member]      
Entity Information [Line Items]      
Entity Common Stock, Shares Outstanding   7,590,811  
Class B [Member]      
Entity Information [Line Items]      
Entity Common Stock, Shares Outstanding   19,024,117