Significant Accounting Policies (Policies)	3 Months Ended
Significant Accounting Policies (Policies)	Mar. 31, 2017
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 interim condensed consolidated financial statements include the accounts of GAMCO and its subsidiaries. Intercompany accounts and transactions are eliminated. These interim 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, 2016.
Use of Estimates	Use of Estimates The preparation of the interim condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported on the interim 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, 2017, 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 consolidated financial statements. In January 2016, the FASB issued ASU 2016-01, which amends the guidance in U.S. GAAP on the classification and measurement of financial instruments. Although the ASU retains many current requirements, it significantly revises an entity’s accounting related to (1) the classification and measurement of investments in equity securities and (2) the presentation of certain fair value changes for financial liabilities measured at fair value. The ASU also amends certain disclosure requirements associated with the fair value of financial instruments. For public companies, the new standard is effective for fiscal years and interim periods within those fiscal years beginning after December 15, 2017. To adopt the amendments, entities will be required to make a cumulative-effect adjustment to beginning retained earnings as of the beginning of the fiscal year in which the guidance is effective. The Company is currently evaluating this guidance and the impact it will have on its consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, which amends the guidance in U.S. GAAP for the accounting for leases. ASU 2016-02 requires a lessee to recognize assets and liabilities arising from most operating leases in the condensed consolidated statement of financial position. ASU 2016-02 is effective beginning January 1, 2019. The Company is currently evaluating this guidance and the impact it will have on its consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, which simplifies several aspects of the accounting for employee share-based payment transactions for both public and nonpublic entities, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification in the statement of cash flows. For public companies, the ASU is effective for annual reporting periods beginning after December 15, 2016, including interim periods within those annual reporting periods. The Company adopted this guidance on January 1, 2017 without a material impact to the consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, which adds and clarifies guidance on the classification of certain cash receipts and payments in the consolidated statements of cash flows. For public companies, the ASU is effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods. Early adoption is permitted. The Company is currently evaluating this guidance and the impact it will have on its consolidated financial statements. In January 2017, the FASB issued ASU 2017-04 to simplify the process used to test for goodwill. Under the new standard, if “the carrying amount of a reporting unit exceeds its fair value, an impairment loss shall be recognized in an amount equal to that excess, limited to the total amount of goodwill allocated to that reporting unit.” For public companies, the ASU is effective for annual and any interim impairment tests for periods beginning after December 15, 2019. Early adoption is permitted for impairment tests that occur after January 1, 2017. The Company is currently evaluating this guidance and the impact it will have on its condensed consolidated financial statements.