Basis of Presentation and Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2017
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 nine months ended September 30, 2017 are not necessarily indicative of the results that may be expected for the year ending December 31, 2017.
Reclassifications	The Company has reclassified certain amounts in prior-period financial statements to conform to the current period's presentation. Previously, the Company reported consolidated investment products and consolidated sponsored investment products separately. Currently, the Company combines these categories under the caption "consolidated investment products" and has accordingly reclassified prior presentations. Further, the Company has reclassified its prior net presentation of purchases and sales of investments by its consolidated sponsored investments products and its consolidated investment product in the Condensed Consolidated Statement of Cash Flows for the nine months ended September 30, 2016 to conform with the current year presentation of showing such purchases and sales as separate line items within the cash flows from operating activities. The reclassifications had no impact on the net cash provided by or used in operating, investing or financing activities within the Condensed Consolidated Statement of Cash Flows, nor any impact on the other Condensed Consolidated Financial Statements.
New Accounting Standards	New Accounting Standards Implemented The Company adopted Accounting Standards Update ("ASU") 2016-09, Improvements to Employee Share-Based Payment Accounting ("ASU 2016-09"), on January 1, 2017. This standard makes several modifications to the accounting for forfeitures and employer tax withholdings on share-based compensation as well as the financial statement presentation of excess tax benefits or deficiencies. ASU 2016-09 also clarifies the statement of cash flows presentation of certain components of share-based awards. Upon adoption, the Company recorded a $1.1 million cumulative effect adjustment to retained earnings for excess tax benefits that were not previously recognized because the related tax deduction had not reduced current taxes payable. The Company elected to adopt all provisions impacting the Condensed Consolidated Statements of Operations and Cash Flows prospectively. The Company adopted ASU 2016-07, Investments - Equity Method and Joint Ventures (Topic 232): Simplifying the Transition to the Equity Method of Accounting, on January 1, 2017. This standard eliminates the requirement that, when an existing cost method investment qualifies for use of the equity method, a reporting entity must restate its historical financial statements, as if the equity method had been used during all previous periods. Under the new guidance, at the point an investment qualifies for the equity method, any unrealized gain or loss in accumulated other comprehensive income/(loss) would be recognized through earnings. The adoption of this standard did not have a material impact on the Company's condensed consolidated financial statements. New Accounting Standards Not Yet Implemented In November 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (“ASU 2016-18”). ASU 2016-18 requires the inclusion of restricted cash with cash and cash equivalents when reconciling the beginning and ending cash on the statement of cash flows. This standard is effective for annual periods beginning after December 15, 2018, and interim periods within fiscal years beginning after December 15, 2017. Early adoption is permitted. A reporting entity is required to apply this standard on a retrospective basis as of the beginning of the fiscal year for which the standard is effective. The Company is currently evaluating the potential impact of this standard on its consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments ("ASU 2016-15"), which 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. This update is effective for annual periods beginning after December 15, 2017 and interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the potential impact of this standard on its consolidated financial statements. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers ("ASU 2014-09"), which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. ASU 2014-09 was originally effective for fiscal years, and interim periods within those years, beginning after December 15, 2016. In August 2015, the FASB issued ASU 2015-14, which deferred the effective date of ASU 2014-09 by one year or for periods beginning after December 15, 2017. Adoption of the standard requires either a retrospective or a modified retrospective approach to adoption, and early adoption is permitted as of the original effective date. The core principle of the model 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. The guidance also changes the accounting for certain contract costs and revises the criteria for determining if an entity is acting as a principal or agent in certain arrangements. This update is effective for annual periods beginning after December 15, 2017 and interim periods within those fiscal years. The Company's implementation assessment includes the identification of revenue within the scope of the guidance, as well as the evaluation of revenue contracts, and it is also evaluating the presentation of certain revenue-related costs on a gross versus net basis and related disclosures of revenue. Although the Company is still evaluating the impact of ASU 2014-09, it has not identified material changes in the timing of revenue recognition. In March 2016, the FASB issued ASU 2016-08, Principal Versus Agent Considerations (Reporting Revenue Gross Versus Net), which amends the principal-versus-agent implementation guidance in ASU 2014-09, Revenue from Contracts with Customers, discussed above. The new guidance will impact whether an entity reports revenue on a gross or net basis. The Company is currently evaluating the potential impact of adopting this standard on its consolidated financial statements, which is effective for the Company in conjunction with the adoption of ASU 2014-09. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) ("ASU 2016-02"). The standard replaces current codification Topic 840 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. ASU 2016-02 is 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 consolidated financial statements but expects to record a right-of-use asset and a related lease obligation in the Company's consolidated balance sheet upon adoption. In January 2016, the FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities ("ASU 2016-01"), which 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. ASU 2016-01 is effective for fiscal years beginning after December 15, 2017 and interim periods therein. Early adoption is not permitted. The Company is currently evaluating the impact of this standard on its consolidated financial statements with respect to equity investments that currently report changes in fair value as a component of accumulated other comprehensive income in equity attributable to stockholders. Comprehensive income, net of tax, with respect to these equity investments was $0.2 million for the year ended December 31, 2016. In January 2017, the FASB issued ASU No. 2017-01, Business Combinations: Clarifying the Definition of a Business ("ASU 2017-01"). The standard clarifies the definition of a business and adds guidance to assist entities when evaluating whether transactions should be accounted for as acquisitions or disposals of assets or as businesses. The standard provides a screen to determine whether a set of assets and activities qualifies as a business or as a set of assets. ASU 2017-01 is effective for fiscal years and interim periods within those years beginning after December 15, 2017. The standard requires a prospective approach to adoption, and early adoption is only permitted for specific transactions. The Company is currently evaluating the impact of this standard on its consolidated financial statements. In January 2017, the FASB issued ASU No. 2017-04, Intangibles - Goodwill and Other: Simplifying the Test for Goodwill Impairment ("ASU 2017-04"). ASU 2017-04 requires that an entity perform its goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity will recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value, but the loss cannot exceed the total amount of goodwill allocated to the reporting unit. ASU 2017-04 is effective for fiscal years and interim periods within those years beginning after December 15, 2019. The amendments require a prospective approach to adoption, and early adoption is permitted for interim or annual goodwill impairment tests. The Company is currently evaluating the impact of this standard on its 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 mutual funds and closed-end funds 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 is 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 they are primarily traded and are categorized as Level 1. Investment in collateralized loan obligations is measured at fair value based on independent third party valuations and is categorized as 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-US 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.
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; (2) 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 (3) if the book value no longer represents fair value.
Consolidation and Nonconsolidated VIEs	The condensed consolidated financial statements include the accounts of the Company, its subsidiaries and investment products that are consolidated. Voting interest entities ("VOEs") are consolidated when the Company is considered to have a controlling financial interest, which is typically present when the Company owns a majority of the voting interest in an entity or otherwise has the power to govern the financial and operating policies of the entity. The Company evaluates any variable interest entities ("VIEs") in which the Company has a variable interest for consolidation. A VIE is an entity in which either: (a) the equity investment at risk is not sufficient to permit the entity to finance its own activities without additional financial support; or (b) where as a group, the holders of the equity investment at risk do not possess: (i) the power through voting or similar rights to direct the activities that most significantly impact the entity’s economic performance, (ii) the obligation to absorb expected losses or the right to receive expected residual returns of the entity or (iii) proportionate voting and economic interests and where substantially all of the entity’s activities either involve or are conducted on behalf of an investor with disproportionately fewer voting rights. If an entity has any of these characteristics, it is considered a VIE and is required to be consolidated by its primary beneficiary. The primary beneficiary is the entity that has both the power to direct the activities that most significantly impact the VIE’s economic performance and has the obligation to absorb losses of, or the right to receive benefits from, the VIE that could potentially be significant to the VIE. In the normal course of its business, the Company sponsors various investment products, some of which are consolidated by the Company. Consolidated investment products include both VOEs, made up primarily of open-end funds in which the Company holds a controlling financial interest, and VIEs, which primarily consist of collateralized loan obligations ("CLOs") of which the Company is considered the primary beneficiary. The consolidation and deconsolidation of these investment products have no impact on net income (loss) attributable to stockholders. The Company’s risk with respect to these investment products is limited to its beneficial interests in these products. The Company has no right to the benefits from, and does not bear the risks associated with, these investment products beyond the Company’s investments in, and fees generated from, these products. 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.