CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION UNAUDITED (Parenthetical) (USD $)	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010
ASSETS
Cash and cash equivalents, restricted cash	$ 0	$ 0	$ 62,308,000
LIABILITIES AND EQUITY
Zero coupon subordinated debentures, face value	$ 86,400,000	$ 86,400,000	$ 0
GAMCO Investors, Inc. stockholders equity
Treasury stock, shares (in shares)	6,934,243	6,492,282	6,232,079
Common Class A [Member]
GAMCO Investors, Inc. stockholders equity
Common Stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Common Stock, shares authorized (in shares)	100,000,000	100,000,000	100,000,000
Common Stock, issued (in shares)	13,600,897	13,255,503	13,202,489
Common Stock, outstanding (in shares)	6,666,654	6,763,221	6,970,140
Common Class B [Member]
GAMCO Investors, Inc. stockholders equity
Common Stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Common Stock, shares authorized (in shares)	100,000,000	100,000,000	100,000,000
Common Stock, issued (in shares)	24,000,000	24,000,000	24,000,000
Common Stock, outstanding (in shares)	20,106,746	20,290,140	20,292,104