Basis of Presentation and Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 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 three months ended March 31, 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 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 ("FASB") issued Accounting Standards Update ("ASU") 2018-09, Codification Improvements. On January 1, 2019, the Company adopted this standard. This standard which does not prescribe any new accounting guidance, makes minor improvements and clarifications of several different FASB Accounting Standards Codification ("ASC") areas based on comments and suggestions made by various stakeholders. 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. The 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) ("ASU 2016-02"). The standard replaces current codification Topic 840 - Leases with updated guidance on accounting for leases that requires a lessee to recognize assets and liabilities arising from an operating lease on the balance sheet, whereas previous guidance did not require lease assets and liabilities to be recognized for most operating leases. Furthermore, this standard permits companies to make an accounting policy election to not recognize lease assets and liabilities on the balance sheet for leases with a term of 12 months or less. For both finance leases and operating leases, the lease liability should be initially measured at the present value of the future lease payments. In addition to recognizing the lease liability, companies are required to recognize a corresponding asset representing the right to use the underlying asset over the lease term. The right of use asset ("ROU") is initially measured as the value of the lease liability, plus indirect costs and prepaid lease payments, less lease incentives. In July 2018, the FASB issued ASU 2018-10, Codification Improvements to Topic 842 (Leases), which provides narrow amendments to clarify how to apply certain aspects of ASU 2016-02, allowing entities the option to instead apply the provisions of the new lease standards 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 guidance which resulted in not having to reassess whether expired or existing contracts upon adoption contained a lease as well as retaining the historical classifications of the Company's leases and initial direct costs. The Company also elected the hindsight practical expedient in evaluating lessee options and to combine lease and non-lease components in calculating the lease liability and ROU asset for operating leases. The adoption of this standard resulted in the recording of a ROU asset of $20.5 million and lease liability of $28.6 million on January 1, 2019 which represented a non-cash investing 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 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 is currently evaluating the potential impact of the guidance but does not expect 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 last sale or bid) on the exchange on which the securities are primarily traded and are categorized as Level 1. Debt securities 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 consolidated investment products. 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 securities that are not widely traded, are illiquid or are priced by dealers based on pricing models used by market makers in the security. Notes payable represent notes issued by consolidated investment products that are CLOs and are measured using the measurement alternative in ASU 2014-13. Accordingly, the fair value of CLO liabilities was 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.
Fair Value Measurements, Transfers	Transfers into and out of levels are reflected when significant inputs used for the fair value measurement, including market inputs or performance attributes, become observable or unobservable or when the Company determines it has the ability, or no longer has the ability, to redeem, in the near term, certain investments that the Company values using a net asset value, or if the book value no longer represents fair value.
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.