Investments, Debt and Equity Securities [Abstract] Fair value Marketable Securities Proceeds received from sales of marketable securities Proceeds from Sale and Maturity of Marketable Securities Net realized gains on sale of marketable securities Marketable Securities, Realized Gain (Loss) Earnings Per Share [Abstract] Schedule of Basic and Diluted Earnings Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Shares Excluded from Calculation of Basic and Diluted Earnings Per Share Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Variable Interest Entities -- None. No documentation exists for this element. -- Schedule of Unconsolidated Assets and Liabilities of Equity Method Investments and Company's Risk of Loss Schedule of Variable Interest Entities [Table Text Block] Affiliate Equity [Abstract] Affiliate Equity [Abstract] Affiliate Equity Affiliate Equity [Text Block] Disclosures related to the conditional rights and obligations the company has to acquire Affiliate equity and the redeemable non-controlling interests on the consolidated balance sheets. Disclosure of the impact on the controlling interest's equity of changes in ownership at its Affiliates. New Accounting Pronouncements and Changes in Accounting Principles [Abstract] Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Use of Estimates Use of Estimates, Policy [Policy Text Block] Recently Adopted Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Investments in Affiliates and Affiliate Sponsored Investments Products Consolidation, Policy [Policy Text Block] Fair Value Measurements Fair Value Measurement, Policy [Policy Text Block] Noncontrolling Interest [Abstract] Redeemable Non-Controlling Interests Noncontrolling Interest Disclosure [Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Basis of Presentation and Use of Estimates Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Statement of Cash Flows [Abstract] Cash flow from (used in) operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Adjustments to reconcile Net income to net cash flow from operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Intangible amortization and impairments Amortization of Intangible Assets Depreciation and other amortization Depreciation and Other Amortization The aggregate expense charged against earnings to allocate the cost of tangible assets to periods in which the assets are used and held and to allocate the cost of issuing debt to periods in which the debt is outstanding. As a noncash expense, this element is added back to net income when calculating cash provided by (used in) operations using the indirect method. Deferred income tax provision Deferred Income Tax Expense (Benefit) Equity method income (net) Income (Loss) from Equity Method Investments Distributions of earnings received from equity method investments Proceeds from Equity Method Investment, Distribution Share-based compensation and Affiliate equity expense Share-based Compensation Other non-cash items Other Noncash Income (Expense) Changes in assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Purchases of securities by Affiliate sponsored consolidated products Purchases of Securities by Affiliate Sponsored Consolidated Products Purchases of Securities by Affiliate Sponsored Consolidated Products Sales of securities by Affiliate sponsored consolidated products Sale of Securities by Affiliate Sponsored Consolidated Products Sale of Securities by Affiliate Sponsored Consolidated Products Increase in receivables Increase (Decrease) in Accounts Receivable Increase in other assets Increase (Decrease) in Prepaid Expense and Other Assets Decrease in payables, accrued liabilities and other liabilities Increase (Decrease) in Operating Liabilities Cash flow from operating activities Net Cash Provided by (Used in) Operating Activities Cash flow from (used in) investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Investments in Affiliates Payments to Acquire Interest in Subsidiaries and Affiliates Purchase of fixed assets Payments to Acquire Property, Plant, and Equipment Purchase of investment securities Payments to Acquire Marketable Securities Sale of investment securities Payments for (Proceeds from) Investments Cash flow from (used in) investing activities Net Cash Provided by (Used in) Investing Activities Cash flow from (used in) financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Borrowings of senior debt Proceeds from Issuance of Long-term Debt Repayments of senior debt Repayments of Long-term Debt Repurchase of common stock Payments for Repurchase of Common Stock Issuance of common stock Proceeds from Issuance of Common Stock Dividends paid on common stock Payments of Dividends Distributions to non-controlling interests Payments of Ordinary Dividends, Noncontrolling Interest Affiliate equity issuances and repurchases Proceeds from (Payments for) Affiliate Equity Issuances and Repurchases The net cash inflow (outflow) resulting from the affiliate share transaction. Other financing items Proceeds from (Payments for) Other Financing Activities Cash flow used in financing activities Net Cash Provided by (Used in) Financing Activities Effect of foreign exchange rate changes on cash and cash equivalents Effect of Exchange Rate on Cash and Cash Equivalents Net decrease in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of period Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents at end of period Related Party Transactions [Abstract] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Prior Owner Prior Owner [Member] Prior Owner of entity Affiliated Entity Affiliated Entity [Member] Related Party Transaction [Axis] Related Party Transaction [Axis] Related Party Transaction [Domain] Related Party Transaction [Domain] Private Equity Investment Partnerships of Affiliate Private Equity Investment Partnerships of Affiliate [Member] Private Equity Investment Partnerships of Affiliate [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Other Liabilities Other Liabilities [Member] Related Party Transactions Related Party Transaction [Line Items] Other liabilities Other Liabilities Contingent payment arrangements liability Business Combination, Contingent Consideration, Liability Equity Method Investments and Joint Ventures [Abstract] Schedule of Changes in Equity Method Investments in Affiliates Equity Method Investments [Table Text Block] Fair Value Disclosures [Abstract] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Liability Class [Axis] Liability Class [Axis] Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] Contingent Payment Arrangements Contingent Payment Arrangements [Member] Represents contingent payment arrangements of the entity. Affiliate Equity Obligations Obligations to Related Parties [Member] Represents the obligations of the entity towards related parties. Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Balance, beginning of period Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value Net realized and unrealized (gains) losses Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings and Other Comprehensive Income (Loss) Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings and Other Comprehensive Income (Loss) Purchases and issuances Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Purchases And Issuances Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Purchases And Issuances Settlements and reductions Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Settlements And Reductions Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Settlements And Reductions Balance, end of period Net change in unrealized (gains) losses relating to instruments still held at the reporting date Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss) Debt Disclosure [Abstract] Senior Debt Debt Disclosure [Text Block] Equity Method Investments in Affiliates Equity Method Investments and Joint Ventures Disclosure [Text Block] Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Common Stock Common Stock [Member] Additional Paid-In Capital Additional Paid-in Capital [Member] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Retained Earnings Retained Earnings [Member] Treasury Stock at Cost Treasury Stock [Member] Non-controlling Interests Noncontrolling Interest [Member] Statement Statement [Line Items] Increase (Decrease) in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning Balance (in shares) Common Stock, Shares, Outstanding Beginning Balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Other comprehensive income Other Comprehensive Income (Loss), Net of Tax Share-based compensation Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Common stock issued under share-based incentive plans Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Share repurchases Treasury Stock, Value, Acquired, Cost Method Dividends ($0.40 per share and $0.60 per share) Dividends Issuance costs and other Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs and Other Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs and Other Affiliate equity activity: Affiliate equity expense Affiliate Equity Compensation Expense, Including Adjustments and Portion Attributable to Noncontrolling Interest Affiliate Equity Compensation Expense, Including Adjustments and Portion Attributable to Noncontrolling Interest Issuances Noncontrolling Interest, Increase from Subsidiary Equity Issuance Repurchases Noncontrolling Interest, Increase (Decrease) from Purchase of Interests Noncontrolling Interest, Increase (Decrease) from Purchase of Interests Changes in redemption value of Redeemable non-controlling interests Noncontrolling Interest, Decrease from Redemptions Noncontrolling Interest, Decrease from Redemptions Transfers to Redeemable non-controlling interests Noncontrolling Interest, Decrease from Transfers to Noncontrolling Interest Holders Noncontrolling Interest, Decrease from Transfers to Noncontrolling Interest Holders Capital contributions by Affiliate equity holders Noncontrolling Interest, Increase from Contributions from Affiliate Noncontrolling Interest, Increase from Contributions from Affiliate Distributions to non-controlling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Ending Balance (in shares) Ending Balance Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Schedule of Share-Based Compensation Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block] Schedule of Company Stock Option Transactions Share-based Compensation, Activity [Table Text Block] Schedule of Fair Value of Options Granted and Assumptions Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Schedule of Company Restricted Stock Unit Transactions Schedule of Nonvested Share Activity [Table Text Block] Commitments and Contingencies Disclosure [Abstract] Commitment and Contingencies [Table] Commitment and Contingencies [Table] Represents commitments and contingencies of the entity. Consolidated Affiliates Consolidated Entities [Member] Equity Method Investee Equity Method Investee [Member] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Scenario, Forecast Scenario, Forecast [Member] Commitments and Contingencies Commitment and Contingencies [Line Items] -- None. No documentation exists for this element. -- Co-investment commitments in partnership Investment Commitment, Amount The amount that the entity agreed to co-invest in certain investment partnerships where the entity serves as the general partner. Contingent liability Other Commitment Expected payments of contingent liability Other Commitment Expected Payments Other Commitment Expected Payments Present value of expected payments of contingent liabilities Other Commitment Present Value of Expected Payments Other Commitment Present Value of Expected Payments Goodwill and Intangible Assets Disclosure [Abstract] Goodwill [Roll Forward] Goodwill [Roll Forward] Balance, as of December 31, 2017 Goodwill Foreign currency translation Goodwill, Foreign Currency Translation Gain (Loss) Balance, as of June 30, 2018 Schedule of Changes in Goodwill Schedule of Goodwill [Table Text Block] Schedule of Changes in the Components of Acquired Client Relationships Schedule of Intangible Assets by Major Class [Table Text Block] Tabular disclosure of intangibles assets, in total and by major class, including the gross carrying amount and accumulated amortization. A major class is composed of intangible assets that can be grouped together because they are similar, either by their nature or by their use in the operations of a company. Noncontrolling Interest [Table] Noncontrolling Interest [Table] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Noncontrolling Interest [Line Items] Noncontrolling Interest [Line Items] Term of conditional right to put interest Term Of Conditional Right to Put Interest Term Of Conditional Right to Put Interest Redeemable Noncontrolling Interest [Roll Forward] Redeemable Noncontrolling Interest [Roll Forward] -- None. No documentation exists for this element. -- Balance, as of December 31, 2017 Redeemable Noncontrolling Interest, Equity, Carrying Amount Changes attributable to consolidated products Noncontrolling Interest, Increase (decrease) Attributable to Consolidated Partnerships Noncontrolling Interest, Increase (decrease) Attributable to Consolidated Partnerships Transfers to Other liabilities Noncontrolling Interest, Decrease from Transfers to Other Liabilities Noncontrolling Interest, Decrease from Transfers to Other Liabilities Transfers from Non-controlling interests Changes in redemption value Redeemable Noncontrolling Interest Change in Redemption Value Increase (decrease) in redeemable non-controlling interests during the period as a result of a change in the redemption value. Balance, as of June 30, 2018 Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table] Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table] Investment Type [Axis] Investment Type [Axis] Investment Type Categorization [Domain] Investments [Domain] Other Investments Other than Securities Investment [Member] Private Equity Funds Private Equity Funds [Member] Other Funds Other Funds [Member] Investments held in other funds. Controlling Interest Parent [Member] NAV of investments at fair value Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] Fair Value Alternative Investment, Fair Value Disclosure Unfunded Commitments Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments Life of funds (in years) Fair Value, Investments, Entities That Calculate NAVs, Life of Fund Fair Value, Investments, Entities That Calculate NAVs, Life of Fund Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Acquired Client Relationships Customer Relationships [Member] Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Investment One Sole Significant Equity Method Affiliate [Member] Sole Significant Equity Method Affiliate Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Amortization expense during the period Estimated Future Amortization Expense of Finite-Lived Intangibles Finite-Lived Intangible Assets, Net, Amortization Expense, Rolling Maturity [Abstract] Finite-lived intangible, future amortization expense in 2018 Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months Finite-lived intangible, future amortization expense in 2019 Finite-Lived Intangible Assets, Amortization Expense, Year Two Finite-lived intangible, future amortization expense in 2020 Finite-Lived Intangible Assets, Amortization Expense, Year Three Finite-lived intangible, future amortization expense in 2021 Finite-Lived Intangible Assets, Amortization Expense, Year Four Finite-lived intangible, future amortization expense in 2022 Finite-Lived Intangible Assets, Amortization Expense, Year Five Impairment recognized on equity method investment in affiliate Equity Method Investment, Other than Temporary Impairment Impairment recognized on equity method investment in affiliate, net of tax Equity Method Investment, Other than Temporary Impairment, Net of Tax Equity Method Investment, Other than Temporary Impairment, Net of Tax Carrying value of equity method investment in affiliate Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Revenue from equity method investment in affiliate Equity Method Investment, Summarized Financial Information, Revenue Net income from equity method investment in affiliate Equity Method Investment, Summarized Financial Information, Net Income (Loss) Schedule of Intangible Assets, by Major Class [Table] Schedule of Intangible Assets, by Major Class [Table] Tabular disclosure of the major classes of acquired finite-lived and indefinite-lived intangible assets showing the amount, any significant residual value, weighted average amortization period, and other characteristics. A major class is composed of intangible assets that can be grouped together because they are similar, either by nature or by their use in the operations of the company. Intangible Assets Intangible Asset [Line Items] -- None. No documentation exists for this element. -- Definite-lived Finite-lived Intangible Assets [Roll Forward] Beginning balance, gross book value Finite-Lived Intangible Assets, Gross Beginning balance, accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Beginning balance, net book value Finite-Lived Intangible Assets, Net Amortization and impairments Impairment of Intangible Assets, Finite-lived Foreign currency translation Finite Lived Intangible Assets, Foreign Currency Translation Gain (Loss) Ending balance, gross book value Ending balance, accumulated amortization Ending balance, net book value Indefinite-lived Indefinite-lived Intangible Assets [Roll Forward] Beginning balance, net book value Indefinite-Lived Intangible Assets (Excluding Goodwill) Intangible amortization and impairments Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill) Foreign currency translation Indefinite-lived Intangible Assets, Foreign Currency Translation Gain (Loss) Ending balance, net book value Total Intangible Assets [Roll Forward] -- None. No documentation exists for this element. -- Beginning balance, net book value Intangible Assets, Net (Excluding Goodwill) Amortization and impairments Impairment of Intangible Assets (Excluding Goodwill) Foreign currency translation Intangible Assets Net Excluding Goodwill Translation Adjustments Represents the amount of increase (decrease) to assets, excluding financial assets and goodwill, for foreign currency translation adjustments. Ending balance, net book value Earnings Per Share Earnings Per Share [Text Block] Other Comprehensive Income (Loss), Net of Tax [Abstract] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Foreign Currency Translation Adjustment Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest [Member] Change in net realized and unrealized gain (loss) on derivative securities Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] Change in net unrealized gain (loss) on investment securities Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member] Change in net unrealized gain (loss) on investment securities attributable to noncontrolling interest Accumulated Net Investment Gain (Loss) Attributable to Noncontrolling Interest [Member] Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) [Line Items] Pre-Tax Other Comprehensive Income (Loss), before Tax Tax Benefit (Expense) Other Comprehensive Income (Loss), Tax Other comprehensive income (loss) Income Tax Disclosure [Abstract] Schedule of Income Tax Provisions by Controlling and Noncontrolling Interests Schedule of Components of Income Tax (Expense) Benefit by Controlling and Noncontrolling interests [Table Text Block] Tabular disclosure of the components of income tax expense attributable to controlling and non-controlling interests for each year presented including, income before income taxes and effective tax rate attributable to controlling interests. Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Unsecured Debt Unsecured Debt [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Revolver Senior Unsecured Credit Facility [Member] Represents the senior unsecured credit facility entered into by the entity during the reporting period. Term Loan Senior Unsecured Term Loan [Member] Senior Unsecured Term Loan Long-term debt Debt Instrument [Line Items] Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Principal amount at maturity Debt Instrument, Face Amount Maximum borrowing capacity, additional amount Line of Credit Facility, Maximum Borrowing Capacity, Additional Amount Line of Credit Facility, Maximum Borrowing Capacity, Additional Amount Dividends per share (in dollars per share) Common Stock, Dividends, Per Share, Cash Paid Change in Equity Method Investments in Affiliates [Roll Forward] Change in Equity Method Investments in Affiliates [Roll Forward] Change in Equity Method Investments in Affiliates Balance, as of December 31, 2017 Equity method earnings Income (Loss) from Equity Method Investments Before Amortization of Intangibles Income (Loss) from Equity Method Investments Before Amortization of Intangibles Equity method intangible amortization and impairments Equity Method Investment, Intangible Asset Amortization and Impairments Equity Method Investment, Intangible Asset Amortization and Impairments Distributions of earnings from equity method investments Foreign currency translation Equity Method Investment, Realized Gain (Loss) on Foreign Currency Translation Equity Method Investment, Realized Gain (Loss) on Foreign Currency Translation Other Equity Method Investment, Other Increase (Decrease) Equity Method Investment, Other Increase (Decrease) Balance, as of June 30, 2018 Provisional one-time net benefit from changes in U.S. tax laws Tax Cuts And Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit) Tax Cuts And Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit) Changes in provisional amount of initial one-time benefit recorded resulting from change in U.S. tax laws Tax Cuts And Jobs Act Of 2017, Measurement Period Adjustment, Income Tax Expense (Benefit) Tax Cuts And Jobs Act Of 2017, Measurement Period Adjustment, Income Tax Expense (Benefit) Goodwill and Acquired Client Relationships Goodwill and Intangible Assets Disclosure [Text Block] Statement of Financial Position [Abstract] Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized (in shares) Common Stock, Shares Authorized Common stock, shares outstanding (in shares) Treasury stock, at cost (in shares) Treasury Stock, Common, Shares Marketable Securities [Abstract] Investments in Marketable Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Related Party Transactions Related Party Transactions Disclosure [Text Block] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Variable Interest Entities [Axis] Variable Interest Entities [Axis] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Classification [Domain] Affiliate sponsored investment products Sponsored Investment Funds [Member] Represents investment funds in to which the entity is not the primary beneficiary of these VIEs. Variable Interest Entities Variable Interest Entity [Line Items] Unconsolidated VIE Net Assets Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net Carrying Value and Maximum Exposure to Loss Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Numerator Net Income (Loss) Available to Common Stockholders, Basic [Abstract] Net income (controlling interest) Net Income (Loss) Attributable to Parent Interest expense on convertible securities, net of taxes Interest on Convertible Debt, Net of Tax Net income (controlling interest), as adjusted Net Income (Loss) Available to Common Stockholders, Diluted Denominator Weighted Average Number of Shares Outstanding, Diluted [Abstract] Average shares outstanding (basic) (in shares) Weighted Average Number of Shares Outstanding, Basic Effect of dilutive instruments: Incremental Weighted Average Shares Attributable to Dilutive Effect [Abstract] Stock options and restricted stock (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Convertible securities (in shares) Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities Average shares outstanding (diluted) (in shares) Weighted Average Number of Shares Outstanding, Diluted Subsequent Events [Abstract] Subsequent Events Subsequent Events [Text Block] Statement of Comprehensive Income [Abstract] Other comprehensive income (loss): Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract] Foreign currency translation gain (loss) Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Change in net realized and unrealized gain (loss) on derivative securities, net of tax Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax Change in net unrealized gain (loss) on investment securities, net of tax Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Comprehensive income (non-controlling interests) Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Comprehensive income (controlling interest) Comprehensive Income (Loss), Net of Tax, Attributable to Parent Share-based compensation Allocated Share-based Compensation Expense Tax benefit Employee Service Share-based Compensation, Tax Benefit from Compensation Expense Compensation expense related to share-based compensation Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Weighted average period over which compensation expense will be recognized Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Increase / (decrease) in controlling interest paid-in capital from Affiliate equity issuances Adjustments to Additional Paid in Capital Increase (Decrease) in Carrying Amount of Redeemable Noncontrolling Interests The increase (decrease) in additional paid-in capital of the reporting entity from purchases and sales of Affiliate equity. Increase / (decrease) in controlling interest paid-in capital from Affiliate equity repurchases Adjustments to Additional Paid in Capital Decrease in Carrying Amount of Redeemable Noncontrolling Interests Adjustments to Additional Paid in Capital Decrease in Carrying Amount of Redeemable Noncontrolling Interests Net income (controlling interest) including net impact of Affiliate equity transactions Increase (Decrease) in Equity Due to Profit (Loss) and Net Transfers with Noncontrolling Interests Increase (decrease) in equity during the period due to net income attributable to the parent company and net transfers with non-controlling interests. Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Carrying Value Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Level 2 Fair Value, Inputs, Level 2 [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Senior notes Notes Payable, Fair Value Disclosure Convertible securities Convertible Debt, Fair Value Disclosures Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Award Type [Axis] Award Type [Axis] Award Type [Domain] Equity Award [Domain] Restricted Stock Restricted Stock [Member] Share-based Compensation Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Restricted Stock Units Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Unvested units at the beginning of the period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Units granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Units vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Units forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Unvested units at the end of the period (in shares) Weighted Average Grant Date Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Unvested units at the beginning of the period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Units granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Units vested (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Units forfeited (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Unvested units at the end of the period (in dollars per share) Restricted stocks granted, fair value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Restricted stock, vesting period (in years) Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Income Statement [Abstract] Consolidated revenue Asset Management Fees Consolidated expenses: Operating Expenses [Abstract] Compensation and related expenses Labor and Related Expense Selling, general and administrative Selling, General and Administrative Expense Interest expense Interest Expense Other expenses (net) Other Cost and Expense, Operating Total consolidated expenses Operating Expenses Equity method income (net) Investment and other income Investment and Other Income (Loss) The amount of income from cost method investments, foreign currency transaction gain or loss and other income recognized during the period. Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) Net income Net income (non-controlling interests) Noncontrolling Interest in Net Income (Loss) Other Noncontrolling Interests, Redeemable Net income (controlling interest) Average shares outstanding (diluted) (in shares) Earnings per share (basic) (in dollars per share) Earnings Per Share, Basic Earnings per share (diluted) (in dollars per share) Earnings Per Share, Diluted Income Tax Provision [Table] Income Tax Provision [Table] Schedule reflecting information of income tax attributable to controlling and noncontrolling interests. Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Controlling Interest Parent Company [Member] Income Tax Provision Income Tax [Line Items] -- None. No documentation exists for this element. -- Current tax Current Income Tax Expense (Benefit) Intangible-related deferred taxes Deferred Income Tax Expense Related to Intangibles The component of income tax expense for the period representing the tax effect of the difference between amortization of intangibles for book purposes and amortization of intangibles for tax purposes. Other deferred taxes Deferred Other Tax Expense (Benefit) Deferred taxes Provision for income taxes Income before income taxes (controlling interest) Income (Loss) from Continuing Operations before Income Taxes Attributable to Parent This element represents the income or loss from continuing operations, before income taxes, which is attributable to the controlling interest. Effective tax rate (controlling interest) Income Tax Expense from Controlling Interest to Pretax, Income from Continued Operations Attributable to Controlling Interest Ratio A ratio calculated by dividing the amount of income tax expense attributable to the controlling interest by pretax income from continuing operations attributable to the controlling interest. Fair Value Measurements Fair Value Disclosures [Text Block] Realized and Unrealized Gains (Losses) on Derivative Securities Total AOCI Including Portion Attributable to Noncontrolling Interest [Member] Components of Accumulated other comprehensive income, net of taxes AOCI Attributable to Parent, Net of Tax [Roll Forward] Other comprehensive income before reclassifications Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Amounts reclassified Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Schedule of Fair Value of Assets and Liabilities Measured on a Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Schedule of Changes in Level 3 Assets and Liabilities Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Schedule of Quantitative Information used in Valuing Level 3 Liabilities Fair Value Inputs, Liabilities, Quantitative Information [Table Text Block] Schedule of Investments in Certain Entities that Calculate Net Asset Value Fair Value Measurement, Inputs Based on Net Assets [Table Text Block] Tabular disclosure of investments that rely on net asset value as their fair value, including the nature of the investment and any related liquidation restrictions. Schedule of Financial Assets and Liabilities Not Carried at Fair Value Summary of Other Financial Liabilities Not Carried at Fair Value [Table Text Block] Summary of Other Financial Liabilities Not Carried at Fair Value [Table Text Block] Number or shares repurchased during period (in shares) Treasury Stock, Shares, Acquired Average price of shares repurchased during period (in dollars per share) Treasury Stock Acquired, Average Cost Per Share Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value Measured On A Recurring Basis Fair Value, Measurements, Recurring [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Fair value of financial assets and liabilities Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Financial Assets Assets, Fair Value Disclosure [Abstract] Cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Investments Investments, Fair Value Disclosure Foreign currency forward contracts Foreign Currency Contract, Asset, Fair Value Disclosure Financial Liabilities Liabilities, Fair Value Disclosure [Abstract] Contingent payment arrangements Obligations, Fair Value Disclosure Affiliate equity obligations Due to Related Parties, Fair Value Disclosure Due to Related Parties, Fair Value Disclosure Foreign currency forward contracts Foreign Currency Contracts, Liability, Fair Value Disclosure Investments in Affiliates and Affiliate Sponsored Investment Products Variable Interest Entities Disclosure [Text Block] This element represents the disclosure of variable interest entities (VIE), including, but not limited to the nature, purpose, size, and activities of the VIE, the carrying amount and classification of consolidated assets that are collateral for the VIE's obligations, lack of recourse if creditors (or beneficial interest holders) of a consolidated VIE have no recourse to the general credit of the primary beneficiary. Which also include information related to Sponsored Investment Funds and Trust Preferred Vehicles related to variable interest entities (VIE). Schedule of Investments in Marketable Securities Marketable Securities [Table Text Block] Comprehensive Income Comprehensive Income (Loss) Note [Text Block] Schedule of Tax Effects Allocated to Each Component of Other Comprehensive Income Comprehensive Income (Loss) [Table Text Block] Schedule of Components of Accumulated Other Comprehensive Income Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Fair Value Inputs, Liabilities, Quantitative Information [Table] Fair Value Inputs, Liabilities, Quantitative Information [Table] Valuation Technique [Axis] Valuation Technique [Axis] Valuation Technique [Domain] Valuation Technique [Domain] Discounted Cash Flow Discounted Cash-Flow Valuation Technique [Member] Represents the discounted cash flow technique used to measure fair value. Affiliate Equity Obligations Quantitative information for Level 3 Fair Value Measurements Liabilities Fair Value Inputs, Liabilities, Quantitative Information [Line Items] Fair value liabilities Financial and Nonfinancial Liabilities, Fair Value Disclosure Growth rate (as a percent) Fair Value Inputs Growth Rates Represents percentage of assumed growth rates, used as an input to measure fair value. Discount rate (as a percent) Fair Value Inputs, Discount Rate Assets Assets [Abstract] Cash and cash equivalents Receivables Accounts Receivable, Net Goodwill Acquired client relationships (net) Equity method investments in Affiliates (net) Fixed assets (net) Property, Plant and Equipment, Net Investments and other assets Investments and Other Assets Investments and Other Assets Total assets Assets Liabilities and Equity Liabilities and Equity [Abstract] Payables and accrued liabilities Accounts Payable and Accrued Liabilities Senior debt Long-term Debt Convertible securities Convertible Debt Deferred income tax liability (net) Deferred Income Tax Liabilities, Net Total liabilities Liabilities Commitments and contingencies (Note 5) Commitments and Contingencies Redeemable non-controlling interests Equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Common stock ($0.01 par value, 153.0 shares authorized; 58.5 shares outstanding in 2017 and 2018) Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital, Common Stock Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss) Attributable to Parent, Net of Tax Accumulated change in equity applicable to the parent entity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge. Retained earnings Retained Earnings (Accumulated Deficit) Total stockholders' equity before treasury stock Stockholders' Equity before Treasury Stock Less: Treasury stock, at cost (3.4 shares in 2017 and 5.1 shares in 2018) Treasury Stock, Value Total stockholders' equity Stockholders' Equity Attributable to Parent Non-controlling interests Other Noncontrolling Interests Total equity Total liabilities and equity Liabilities and Equity Schedule of Affiliate Equity Compensation Summary of Affiliate Equity Compensation [Table Text Block] Summary of Affiliate Equity Compensation [Table Text Block] Schedule of Affiliate Equity Unrecognized Compensation Expense Summary of Affiliate Equity Unrecognized Compensation Expense [Table Text Block] Summary of Affiliate Equity Unrecognized Compensation Expense [Table Text Block] Schedule of Changes in the Company's Interest in its Affiliates on the Controlling Interest's Equity Schedule of Net Income (Loss) Attributable to Entity and Net Transfers with Noncontrolling Interest [Table Text Block] Represents a schedule of net income (loss) attributable to the entity and net transfers to non-controlling interest. Income Taxes Income Tax Disclosure [Text Block] Subsequent Event [Table] Subsequent Event [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Subsequent Event [Line Items] Subsequent Event [Line Items] Repayments of long-term debt Affiliate Equity [Table] Affiliate Equity [Table] Affiliate Equity [Table] Affiliate Equity [Line Items] Affiliate Equity [Line Items] [Line Items] for Affiliate Equity [Table] Controlling interest Compensation Expenses Related to Affiliate Equity Represents the compensation expenses related to Affiliate equity. Non-controlling interests Affiliate Equity Compensation Expense, Attributable to Noncontrolling Interest Affiliate Equity Compensation Expense, Attributable to Noncontrolling Interest Affiliate equity expense Affiliate Equity Compensation Expense, Including Portion Attributable to Noncontrolling Interest Affiliate Equity Compensation Expense, Including Portion Attributable to Noncontrolling Interest Unrecognized Affiliate Equity Expense [Abstract] Unrecognized Affiliate Equity Expense [Abstract] Unrecognized Affiliate Equity Expense [Abstract] Controlling Interest Unrecognized Compensation Expenses Related to Affiliate Equity Attributable to Controlling Interest Unrecognized Compensation Expenses Related to Affiliate Equity Attributable to Controlling Interest Remaining Life (in years) Affiliate Equity, Unrecognized Compensation Expense, Weighted Average Period of Recognition Affiliate Equity, Unrecognized Compensation Expense, Weighted Average Period of Recognition Non-Controlling Interest Affiliate Equity Unrecognized Compensation Expense, Attributable to Noncontrolling Interest Affiliate Equity Unrecognized Compensation Expense, Attributable to Noncontrolling Interest Document and Entity Information -- None. No documentation exists for this element. -- Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Current Fiscal Year End Date Current Fiscal Year End Date Entity Current Reporting Status Entity Current Reporting Status Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Affiliates accounted for under the equity method Variable Interest Entities Previously Accounted for Under the Equity Method [Member] Variable Interest Entities Previously Accounted for Under the Equity Method Carrying Value and Maximum Exposure to Loss Variable Interest Entity, Nonconsolidated, Comparison of Carrying Amount of Assets and Liabilities to Maximum Loss Exposure Schedule of Changes in Redeemable Non-Controlling Interests Redeemable Noncontrolling Interest [Table Text Block] Cost Marketable Securities, Cost Marketable Securities, Cost Unrealized gains Marketable Securities, Unrealized Gains Marketable Securities, Unrealized Gains Unrealized losses Marketable Securities, Unrealized Losses Marketable Securities, Unrealized Losses Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Intangible amortization and impairments Intangible Amortization and Impairments [Member] Intangible Amortization and Impairments Amortization and impairment expenses of intangible assets Share-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Stock options and restricted stock units Employee Stock Options and Restricted Stock [Member] Employee Stock Options and Restricted Stock [Member] Convertible securities Convertible Debt Securities [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive securities excluded from computation of earnings per share (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Accounting Standards and Policies New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Stock Options Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Unexercised options outstanding at the beginning of the period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Options granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Options exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Options forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Unexercised options outstanding at the end of the period (in shares) Exercisable at the end of the period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Unexercised options outstanding at the beginning of the period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Options granted (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Options exercised (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Options forfeited (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Unexercised options outstanding at the end of the period (in dollars per share) Exercisable at the end of the period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Weighted Average Remaining Contractual Life Share-based Compensation Arrangement by Share-based Payment Award, Options, Weighted Average Remaining Contractual Life [Abstract] -- None. No documentation exists for this element. -- Unexercised options outstanding at the end of the period (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Exercisable at the end of the period (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Other Assets Other Assets [Member] Distributions paid to affiliate partners Payments to acquire interest in affiliates Payments to Acquire Businesses and Interest in Affiliates Issuance of interest in affiliates Proceeds from Divestiture of Businesses and Interests in Affiliates Due from affiliates Due from Affiliates Due to affiliates Due to Affiliate Stock Options Employee Stock Option [Member] Stock options granted, fair value Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value Stock options, vesting period (in years) Stock options, expiration period (in years) Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Stock options granted, weighted average fair value (in dollar per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Expected volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Risk-fee interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Expected life of options (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Forfeiture rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions Forfeiture Rate Represents the expected rate the entity will cancel the stock option awards due to nonfulfillment of certain conditions of equity-based compensation arrangements.