Significant Accounting Policies (Policies)	9 Months Ended
Significant Accounting Policies (Policies)	Sep. 30, 2014
Significant Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation Unless we have indicated otherwise, or the context otherwise requires, references in this report to "GAMCO Investors, Inc.," "GAMCO," "the Company," "GBL," "we," "us" and "our" or similar terms are to GAMCO Investors, Inc., its predecessors and its subsidiaries. The unaudited interim condensed consolidated financial statements of GAMCO included herein have been prepared in conformity with generally accepted accounting principles ("GAAP") in the United States for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all the information and footnotes required by U.S. GAAP in the United States for complete financial statements. In the opinion of management, the unaudited interim condensed consolidated financial statements reflect all adjustments, which are of a normal recurring nature, necessary for a fair presentation of financial position, results of operations and cash flows of GAMCO for the interim periods presented and are not necessarily indicative of a full year's results. The condensed consolidated financial statements include the accounts of GAMCO and its subsidiaries. Intercompany accounts and transactions are eliminated. These condensed consolidated financial statements should be read in conjunction with our audited consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2013 from which the accompanying condensed consolidated financial statements were derived.
Use of Estimates	Use of Estimates The preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported on the condensed consolidated financial statements and accompanying notes. Actual results could differ from those estimates.
Recent Accounting Developments	Recent Accounting Developments In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2014-09, "Revenue from Contracts with Customers," which supersedes the revenue recognition requirements in the Accounting Standards Codification ("Codification") Topic 605, Revenue Recognition, and most industry-specific guidance throughout the Industry Topics of the Codification. The core principle of the new ASU No. 2014-09 is for companies to recognize revenue from the transfer of goods or services to customers in amounts that reflect the consideration to which the company expects to be entitled in exchange for those goods or services. The new standard provides a five-step approach to be applied to all contracts with customers and also requires expanded disclosures about revenue recognition. The ASU is effective for annual reporting periods beginning after December 15, 2016, including interim periods and is to be retrospectively applied. Early adoption is not permitted. The Company is currently evaluating this guidance and the impact it will have on its condensed consolidated financial statements. In June 2014, the FASB issued an accounting update clarifying that entities should treat performance targets that could be met after the requisite service period of a share-based payment award as performance conditions that affect vesting. Therefore, an entity would not record compensation expense (measured as of the grant date) for an award where transfer to the employee is contingent upon satisfaction of the performance target until it becomes probable that the performance target will be met. The guidance is effective for the Company beginning January 1, 2016. Early adoption is permitted. This guidance is not expected to have a material impact on the Company's condensed consolidated financial statements.