CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME UNAUDITED - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME UNAUDITED [Abstract]
Net income	$ 35,016		$ 16,600		$ 93,859	$ 64,314
Other comprehensive gain/(loss), net of tax:
Foreign currency translation	(13)		28		16	75
Net unrealized gain/(loss) on securities available for sale	0	[1]	2,321	[1]	0	1,019
Other comprehensive gain/(loss)	(13)		2,349		16	1,094
Comprehensive income attributable to GAMCO Investors, Inc.	$ 35,003		$ 18,949		$ 93,875	$ 65,408

[1] Net of income tax expense/(benefit) of $0, $739, $0 and ($765), respectively. Effective January 1, 2018, upon the adoption of ASU 2016-01, the Company no longer recognizes unrealized gains or losses on equity securities through other comprehensive gain/(loss). See Note C.