CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME UNAUDITED - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME UNAUDITED [Abstract]
Net income		$ 27,261	$ 24,820
Other comprehensive gain/(loss), net of tax:
Foreign currency translation		89	10
Net unrealized gains/(losses) on securities available for sale	[1]	0	(2,561)
Other comprehensive income/(loss)		89	(2,551)
Comprehensive income attributable to GAMCO Investors, Inc. shareholders		$ 27,350	$ 22,269

[1] Net of income tax benefit of $0 and $1,504, 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.