Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Mar. 01, 2016	Jun. 30, 2015
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
Entity Public Float			$ 428,988,824
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2015
Class A [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		10,684,107
Class B [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		19,106,792