Basis of Presentation and Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Basis of Accounting	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 six months ended June 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018. 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, 2017 filed with the Securities and Exchange Commission. The Company’s significant accounting policies, which have been consistently applied, are summarized in its 2017 Annual Report on Form 10-K.
New Accounting Standards	New Accounting Standards Implemented On January 1, 2018, the Company adopted the new Accounting Standards Codification ("ASC") 606, Revenue from Contracts with Customers ("ASC 606"), pursuant to Accounting Standards Update ("ASU") 2014-09, Revenue from Contracts with Customers, and all the related amendments ("the new revenue standard") using the modified retrospective approach. The core principle of the new revenue standard is that revenue is recognized upon the transfer of promised goods or services to customers in an amount that reflects the expected consideration to be received for the goods or services. Based on the revised criteria in the new revenue standard for determining whether the Company is acting as a principal or agent, certain costs that were previously presented on a net of revenue basis are now presented on a gross basis. The comparative periods have not been restated and continue to be reported under the accounting standards in effect for those periods. No cumulative-effect adjustment to the balance sheet was necessary upon the adoption of ASC 606. The adoption of this standard did not have a material impact on the Company's condensed consolidated financial statements. ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities ("ASU 2016-01"). On January 1, 2018, the Company adopted amendments to ASC 825 - Financial Instruments pursuant to ASU 2016-01. This standard requires all equity investments (other than those accounted for under the equity method) to be measured at fair value with changes in the fair value recognized through net income. The Company recorded a $0.2 million cumulative-effect adjustment to the balance sheet upon adoption. ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments ("ASU 2016-15"). On January 1, 2018, the Company adopted amendments to ASC 230 - Statement of Cash Flows ("ASC 230") on a retrospective basis pursuant to ASU 2016-15. This standard clarifies the treatment of several cash flow activities. ASU 2016-15 also clarifies that when cash receipts and cash payments have aspects of more than one classification of cash flows and cannot be separated, classification will depend on the predominant source or use. The adoption of this standard did not have a material impact on the Company's condensed consolidated financial statements. ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash ("ASU 2016-18"). On January 1, 2018, the Company adopted amendments to ASC 230 on a retrospective basis pursuant to ASU 2016-18. This standard requires the inclusion of restricted cash with cash and cash equivalents when reconciling the beginning and ending cash on the statement of cash flows. Restricted cash includes cash pledged or on deposit with brokers of consolidated investment products. Cash, cash equivalents and restricted cash reported on the condensed consolidated statements of cash flows now includes $0.8 million, $0.9 million and $1.0 million of cash pledged or on deposit of consolidated investment products as of December 31, 2017, June 30, 2017, and December 31, 2016, respectively, as well as previously reported cash and cash equivalents. The adoption of this standard did not have a material impact on the Company's condensed consolidated financial statements. ASU 2017-01, Clarifying the Definition of a Business ("ASU 2017-01"). On January 1, 2018, the Company adopted amendments to ASC 805 - Business Combinations ("ASC 805") pursuant to ASU 2017-01, and will apply the standard prospectively. This standard provides guidance on evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The adoption of this standard did not have a material impact on the Company's condensed consolidated financial statements. ASU 2017-04, Intangibles - Goodwill and Other: Simplifying the Accounting for Goodwill Impairment ("ASU 2017-04"). On January 1, 2018, the Company adopted amendments to ASC 350 - Intangibles Goodwill and Other pursuant to ASU 2017-04, and will apply the standard prospectively for all future annual and interim goodwill impairment tests . Under ASU 2017-04, a goodwill impairment is defined to be the amount by which a reporting unit’s carrying value exceeds its fair value. The adoption of this standard did not have a material impact on the Company's condensed consolidated financial statements. ASU 2018-05, Income Taxes (Topic 740), Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118 ("ASU 2018-05"). In March 2018, the Company adopted the amendments to ASC 740 - Income Taxes pursuant to ASU 2018-05. The standard adds various Securities and Exchange Commission ("SEC") paragraphs pursuant to the issuance of the December 2017 SEC Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act ("SAB 118"), which was effective immediately. The SEC issued SAB 118 to address concerns about reporting entities’ ability to comply with the accounting requirements to recognize all of the effects of the Tax Cuts and Jobs Act in the period of enactment on a timely basis. SAB 118 allows disclosure stating that timely determination of some or all of the income tax effects from the Tax Cuts and Jobs Act are incomplete by the due date of the financial statements and if possible to provide a reasonable estimate of the income tax effects. We have accounted for the tax effects of the Tax Cuts and Jobs Act under the guidance of SAB 118, on a provisional basis. Our accounting for certain income tax effects is incomplete, but we have determined reasonable estimates for those effects and have recorded provisional amounts in our condensed consolidated financial statements as of June 30, 2018 and December 31, 2017. New Accounting Standards Not Yet Implemented In July 2018, the FASB issued ASU 2018-09, Codification Improvements ("ASU 2018-09"). This standard does not prescribe any new accounting guidance, but instead makes minor improvements and clarifications of several different FASB ASC areas based on comments and suggestions made by various stakeholders. Certain updates are applicable immediately while other updates provide for a transition period for adoption over the next fiscal year beginning after December 15, 2018. The Company is currently evaluating the potential impact of the guidance but does not expect the adoption of this standard to 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 ("ASU 2018-02"). The standard provides financial statement preparers with an option to reclassify stranded tax effects within accumulated other comprehensive income 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. ASU 2018-02 is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Early adoption is permitted. The Company does not expect the adoption of this guidance to 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 and 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 leases. Furthermore, this standard permits companies to make an accounting policy election to not recognize lease assets and liabilities 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 lease payments. The recognition, measurement and presentation of expenses and cash flows arising from a lease by a lessee will not significantly change under this new guidance. 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. Both standards are effective for fiscal years beginning after December 15, 2018 and interim periods therein. Early adoption is permitted. The Company is currently evaluating the potential impact of this standard on its condensed consolidated financial statements but expects to record a right-of-use asset and a related lease obligation in the Company's condensed consolidated balance sheet upon adoption.
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 mutual funds, closed-end funds and ETFs for which the Company acts as the investment manager. The fair value of open-end mutual 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 are determined based on the official closing price on the exchange on which they are traded and are categorized as Level 1. Equity securities include 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. Investments in collateralized loan obligations represent investments in CLOs for which the Company provides investment management services. The investments in collateralized loan obligations are measured at fair value based on independent third-party valuations and are categorized as Level 2 or Level 3. Nonqualified retirement plan assets represent open-end 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, including bank loan investments, are valued based on quotations received from independent pricing services or from dealers who make markets in such securities. 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 analysis 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.
Fair Value Measurements, Transfers	Transfers into and out of levels are reflected when: (1) significant inputs used for the fair value measurement, including market inputs or performance attributes, become observable or unobservable; or (2) if the book value no longer represents fair value.
Consolidation and Nonconsolidated VIEs	The Company serves as the collateral manager for other collateralized loan and collateralized bond obligations (collectively, "CDOs") that are not consolidated. The assets and liabilities of these CDOs reside in bankruptcy remote, special purpose entities in which the Company has no ownership, nor holds any notes issued by the CDOs, and provides neither recourse nor guarantees. The Company has determined that the investment management fees it receives for serving as collateral manager for these CDOs did not represent a variable interest as: (1) the fees the Company earns are compensation for services provided and are commensurate with the level of effort required to provide the investment management services; (2) the Company does not hold other interests in the CDOs that individually, or in the aggregate, would absorb more than an insignificant amount of the CDO's expected losses or receive more than an insignificant amount of the CDO's expected residual return; and (3) the investment management arrangement only includes terms, conditions and amounts that are customarily present in arrangements for similar services negotiated at arm's length. 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.