CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION UNAUDITED (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Liabilities and Equity
Zero coupon subordinated debentures, face value	$ 10.4	$ 13.1	$ 13.8
GAMCO Investors, Inc. stockholders equity
Preferred Stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Preferred Stock, shares authorized (in shares)	10,000,000us-gaap_PreferredStockSharesAuthorized	10,000,000us-gaap_PreferredStockSharesAuthorized	10,000,000us-gaap_PreferredStockSharesAuthorized
Common Stock, outstanding (in shares)	25,800,000us-gaap_CommonStockSharesOutstanding	25,900,000us-gaap_CommonStockSharesOutstanding	26,000,000us-gaap_CommonStockSharesOutstanding
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)	15,357,733	15,341,433	15,071,087
Common Stock, outstanding (in shares)	6,591,119	6,616,212	6,639,106
Treasury stock, shares (in shares)	8,766,614	8,725,221	8,431,981
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)	19,219,260	19,239,260	19,345,706

This element represents the face value of the Zero coupon subordinated debentures due December 31, 2015.

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Face amount or stated value per share of common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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