Basis of Presentation and Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP") for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, these financial statements contain all adjustments, consisting only of normal recurring adjustments, necessary for a fair statement of the Company’s financial condition and results of operations. Operating results for the nine months ended September 30, 2019 are not necessarily indicative of the results that may be expected for the year ending December 31, 2019. These unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 filed with the Securities and Exchange Commission (the "SEC"). The Company’s significant accounting policies, which have been consistently applied, are summarized in its 2018 Annual Report on Form 10-K.
New Accounting Standards Implemented and Not Yet Implemented	New Accounting Standards Implemented In July 2018, the Financial Accounting Standards Board (the "FASB") issued Accounting Standards Update ("ASU") 2018-09, Codification Improvements. This standard, which does not prescribe any new accounting guidance, clarifies several different FASB Accounting Standards Codification ("ASC") areas based on comments and suggestions made by various stakeholders. On January 1, 2019, the Company adopted this standard. The adoption of this standard did not have a material impact on the Company's condensed consolidated financial statements. In February 2018, the FASB issued ASU 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. This standard provides financial statement preparers with the option to reclassify tax effects within other comprehensive income (referred to as stranded tax effects) to retained earnings in each period in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Cuts and Jobs Act (or portion thereof) is recorded. On January 1, 2019, the Company adopted this standard. The adoption of this standard did not have a material impact on the Company's condensed consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), with several amendments (collectively, "ASU 2016-02"). This standard requires a lessee to recognize assets and liabilities on the balance sheet arising from operating leases. For both finance leases and operating leases, the lease liability is initially measured at the present value of the future lease payments. In addition to the lease liability, companies are required to recognize a corresponding right of use ("ROU") asset representing the right to use the underlying leased asset over the lease term. The right of use asset is initially measured as the value of the lease liability, less indirect costs and prepaid lease payments, less lease incentives. ASU 2016-02 allows entities the option to apply its provisions at the effective date without adjusting comparative periods presented. The Company elected this optional transition method along with the package of practical expedients permitted under the standard, which allowed the Company to forgo (a) reassessing whether expired or existing non-lease contracts that commenced before January 1, 2019 contained an embedded lease, (b) reevaluating the accounting classification of our existing operating leases, and (c) determining whether initial direct costs related to existing leases should be capitalized. The Company also elected to combine lease and non-lease components in calculating the lease liability and ROU asset for operating leases. On January 1, 2019, the Company adopted this standard, which resulted in the recording of a ROU asset of $20.5 million and lease liability of $28.6 million representing a non-cash activity in the Company's Condensed Consolidated Statements of Cash Flows. See Note 8 for further discussion. New Accounting Standards Not Yet Implemented In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40) ("ASU 2018-15"). This standard aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software, including an internal-use software license. ASU 2018-15 is effective for fiscal years beginning after December 15, 2019 and interim periods within those fiscal years. Early adoption is permitted. The Company does not expect that the adoption of this standard will have a material impact on the Company's condensed consolidated financial statements. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820). This standard modifies the disclosure requirements on fair value measurements and is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted. The Company does not expect that the adoption of this standard will have a material impact on the Company's condensed consolidated financial statements.
Fair Value Measurements	The following is a discussion of the valuation methodologies used for the Company’s assets measured at fair value: Cash equivalents represent investments in money market funds. Cash investments in actively traded money market funds are valued using published net asset values and are classified as Level 1. Sponsored funds represent investments in open-end funds, closed-end funds and ETFs for which the Company acts as the investment manager. The fair value of open-end funds is determined based on their published net asset values and are categorized as Level 1. The fair value of closed-end funds and ETFs is determined based on the official closing price on the exchange on which they are traded and are categorized as Level 1. Equity securities represent securities traded on active markets and are valued at the official closing price (typically the last sale or bid) on the exchange on which the securities are primarily traded and are categorized as Level 1. Debt securities and Investments - available for sale primarily represent investments in CLOs for which the Company provides investment management services. The investments in CLOs are measured at fair value based on independent third-party valuations and are categorized as Level 2 and Level 3. The independent third-party valuations are based on discounted cash flow models and comparable trade data. Nonqualified retirement plan assets represent mutual funds within a nonqualified retirement plan whose fair value is determined based on their published net asset value and are categorized as Level 1. Cash, accounts receivable, accounts payable and accrued liabilities equal or approximate fair value based on the short-term nature of these instruments. Cash equivalents represent investments in money market funds. Cash investments in actively traded money market funds are valued using published net asset values and are classified as Level 1. Debt and equity investments represent the underlying debt, equity and other securities held in CIP. Equity investments are valued at the official closing price on the exchange on which the securities are traded and are generally categorized within Level 1. Level 2 investments represent most debt securities, including bank loans and certain equity securities (including non-U.S. securities), for which closing prices are not readily available or are deemed to not reflect readily available market prices, and are valued using an independent pricing service. Debt investments are valued based on quotations received from independent pricing services or from dealers who make markets in such securities. Bank loan investments, which are included as debt investments, are generally priced at the average mid-point of bid and ask quotations obtained from a third-party pricing service. Fair value may also be based upon valuations obtained from independent third-party brokers or dealers utilizing matrix pricing models that consider information regarding securities with similar characteristics. In certain instances, fair value has been determined utilizing discounted cash flow analyses or single broker non-binding quotes. Depending on the nature of the inputs, these assets are classified as Level 1, 2 or 3 within the fair value measurement hierarchy. Level 3 investments include debt and equity securities that are not widely traded, are illiquid or are priced by dealers based on pricing models used by market makers in the security. Derivative assets and liabilities represent futures contracts, swaps contracts, option contracts and forward contracts held in CIP. Derivative instruments in an asset position are classified as other assets of CIP in the Condensed Consolidated Balance Sheets. Derivative instruments in a liability position are classified as liabilities of CIP within the Condensed Consolidated Balance Sheets. The change in fair value of such derivatives is recorded in realized and unrealized gain (loss) on investments of CIP, net, in the Condensed Consolidated Statements of Operations. Depending on the nature of the inputs, these derivative assets and liabilities are classified as Level 1, 2 or 3 within the fair value measurement hierarchy. In connection with entering into these derivative contracts, these CIP may be required to pledge an amount of cash equal to the appropriate “initial margin” requirements. The cash pledged or on deposit is recorded in the Condensed Consolidated Balance Sheets of the Company as Cash pledged or on deposit of CIP. The fair value of such derivatives at September 30, 2019 was immaterial. Notes payable represent notes issued by CLO CIP and are measured using the measurement alternative in ASU 2014-13. Accordingly, the fair value of CLO liabilities is measured as the fair value of CLO assets less the sum of: (a) the fair value of the beneficial interests held by the Company, and (b) the carrying value of any beneficial interests that represent compensation for services.
Consolidation and Nonconsolidated VIEs	The Company has interests in certain other entities that are VIEs that the Company does not consolidate as it is not the primary beneficiary of those entities. The Company is not the primary beneficiary as its interest in these entities does not provide the Company with the power to direct the activities that most significantly impact the entities' economic performance.