Leases [Abstract] Lessee leasing agreements, operating leases, area under lease Lessee Leasing Agreements, Operating Leases, Area under Lease Lessee Leasing Agreements, Operating Leases, Area under Lease Number of office space locations Property Subject to or Available for Operating Lease, Number of Units Operating lease expense excluding rent Operating Lease Expense Excluding Rent Operating Lease Expense Excluding Rent Organization, Consolidation and Presentation of Financial Statements [Abstract] Business and Organization Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Investments, Debt and Equity Securities [Abstract] Total assets Equity Method Investment, Summarized Financial Information, Assets Total liabilities Equity Method Investment, Summarized Financial Information, Liabilities Net assets Equity Method Investment Summarized Financial Information, Equity DHCM's portion of net assets Equity Method Investment, Underlying Equity in Net Assets Investment income Equity Method Investment, Summarized Financial Information, Revenue Expenses Equity Method Investment, Summarized Financial Information, Expenses The amount of expenses reported by an equity method investment of the entity. Net realized gains Equity Method Investment, Summarized Financial Information, Net realized gains (losses) The amount of net realized gains (losses) reported by an equity method investment of the entity. Net change in unrealized appreciation (depreciation) Equity Method Investment, Summarized Financial Information, Net change in unrealized appreciation/depreciation The amount of net change in unrealized appreciation/depreciation reported by an equity method investment of the entity. Net income Equity Method Investment, Summarized Financial Information, Net Income (Loss) DHCM's portion of net income Income (Loss) from Equity Method Investments Disclosure of Compensation Related Costs, Share-based Payments [Abstract] 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] Share-based Compensation Arrangements by Share-based Payment Award, Award Type and Plan Name [Domain] Equity Award [Domain] Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Expense recognition of deferred compensation Deferred Compensation Arrangements [Abstract] 2018 Employee Service Share Based Compensation Nonvested Awards Compensation Cost Not Yet Recognized in Year One Employee service share based compensation nonvested awards compensation cost not yet recognized in year one. 2019 Employee Service Share Based Compensation Nonvested Awards Compensation Cost Not Yet Recognized in Year Two Employee service share based compensation nonvested awards compensation cost not yet recognized in year two. 2020 Employee Service Share Based Compensation Nonvested Awards Compensation Cost Not Yet Recognized in Year Three Employee service share based compensation nonvested awards compensation cost not yet recognized in year three. 2021 Employee Service Share Based Compensation Nonvested Awards Compensation Cost Not Yet Recognized in Year Four Employee service share based compensation nonvested awards compensation cost not yet recognized in year four 2022 Employee Service Share Based Compensation Nonvested Awards Compensation Cost Not Yet Recognized in Year Five Employee service share based compensation nonvested awards compensation cost not yet recognized in year five. Thereafter Employee Service Share Based Compensation Nonvested Awards Compensation Cost Not Yet Recognized Thereafter Employee Service Share Based Compensation Nonvested Awards Compensation Cost Not Yet Recognized Thereafter Total Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Future minimum lease payments under the operating leases Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] Total Operating Leases, Future Minimum Payments Due 2018 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2019 Operating Leases, Future Minimum Payments, Due in Two Years 2020 Operating Leases, Future Minimum Payments, Due in Three Years 2021 Operating Leases, Future Minimum Payments, Due in Four Years 2022 Operating Leases, Future Minimum Payments, Due in Five Years Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Fair value of investments Investments, Fair Value Disclosure Trading Securities [Table] Statement [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Parent Parent [Member] Redeemable Noncontrolling Interest Noncontrolling Interest [Member] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] Securities held in Consolidated Funds Securities held in Consolidated Funds [Member] Securities held in Consolidated Funds [Member] Schedule of Trading Securities and Other Trading Assets [Line Items] Schedule of Trading Securities and Other Trading Assets [Line Items] Trading Securities Trading Securities Statement of Stockholders' Equity [Abstract] Dividend paid per share (in dollars per share) Common Stock, Dividends, Per Share, Cash Paid Income Statement [Abstract] REVENUES: Revenues [Abstract] Investment advisory Investment Advisory Fees Mutual fund administration, net Revenue from Administrative Services Net Revenue from administrative services net. Total revenue Revenues OPERATING EXPENSES: Operating Expenses [Abstract] Compensation and related costs Labor and Related Expense General and administrative General and Administrative Expense Sales and marketing Selling and Marketing Expense Mutual fund administration Asset Management Costs Total operating expenses Operating Expenses NET OPERATING INCOME Operating Income (Loss) Investment income (loss), net Investment Income, Net Gain on sale of subsidiary Gain (Loss) on Disposition of Business INCOME BEFORE TAXES Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) NET INCOME Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Less: Net income attributable to redeemable noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest NET INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS Net Income (Loss) Attributable to Parent Earnings per share attributable to common shareholders Earnings Per Share [Abstract] Basic (per share) Earnings Per Share, Basic Diluted (per share) Earnings Per Share, Diluted Weighted average shares outstanding Weighted Average Number of Shares Outstanding, Diluted [Abstract] Basic (in shares) Weighted Average Number of Shares Outstanding, Basic Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Accounting Policies [Abstract] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Company sponsored investments Company Sponsored Investments [Member] Company Sponsored Investments [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value, Measurements, Recurring Fair Value, Measurements, Recurring [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Level 1 Inputs Fair Value, Inputs, Level 1 [Member] Level 2 Inputs Fair Value, Inputs, Level 2 [Member] Level 3 inputs Fair Value, Inputs, Level 3 [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Trading Investments Compensation Plans Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Statement [Table] Common Stock Common Stock [Member] Deferred Equity Compensation Deferred Compensation, Share-based Payments [Member] Retained Earnings Retained Earnings [Member] Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning Balance, shares Common Stock, Shares, Outstanding Beginning Balance Stockholders' Equity Attributable to Parent Issuance of restricted stock grants Stock Issued During Period, Value, Restricted Stock Award, Gross Issuance of restricted stock grants, shares Stock Issued During Period, Shares, Restricted Stock Award, Gross Amortization of restricted stock grants Amortization Of Restricted Stock Grants Amortization of restricted stock grants. Issuance of stock grants, shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Issuance of stock grants Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Issuance of common stock related to 401k plan match Stock Issued During Period, Value, New Issues Issuance of common stock related to 401k plan match (in shares) Stock Issued During Period, Shares, Employee Benefit Plan Tax benefit from dividend payments related to restricted stock grants Tax Benefit From Dividend Payments Related To Restricted Stock Grants Tax benefit from dividend payments related to restricted stock grants. Net excess tax benefit from vested restricted stock grants Income Tax Effects Allocated Directly to Equity, Equity Transactions Shares withheld related to employee tax withholding Adjustments Related to Tax Withholding for Share-based Compensation Shares withheld related to employee tax withholding (shares) Shares Paid for Tax Withholding for Share Based Compensation Forfeiture of restricted stock grants Stock Issued During Period, Value, Restricted Stock Award, Forfeitures Forfeiture of restricted stock grants, shares Stock Issued During Period, Shares, Restricted Stock Award, Forfeited Cash dividend paid of $5.00 in 2015, $6.00 in 2016, and $7.00 in 2017 per share respectively Dividends, Common Stock, Cash Net income attributable to parent Ending Balance, shares Ending Balance Increase (Decrease) in Temporary Equity [Roll Forward] Increase (Decrease) in Temporary Equity [Roll Forward] Beginning balances attributable to redeemable noncontrolling interests Redeemable Noncontrolling Interest, Equity, Carrying Amount Cumulative-effect adjustment from the adoption of ASU 2015-02 (Note 2) Cumulative Effect of New Accounting Principle in Period of Adoption Net Income Attributable to Redeemable Noncontrolling Interest Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Net subscriptions of consolidated funds Subscription From Redemption Distribution To Noncontrolling Interest A positive value represents subscriptions net of redemptions and distributions to redeemable non-controlling interest holders. A negative value represents redemptions and distributions paid to redeemable non-controlling interest holders net of subscriptions received. Ending balances attributable to redeemable noncontrolling interests Income Tax Disclosure [Abstract] Summary of reconciliation of income tax expense Effective Income Tax Rate Reconciliation, Amount [Abstract] Income tax computed at statutory rate Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Benefit attributable to redeemable noncontrolling interests Effective Income Tax Rate Reconciliation, Noncontrolling Interest Income (Loss), Amount City and state income taxes, net of federal benefit Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Revaluation adjustment of net deferred tax assets Effective Income Tax Rate Reconciliation, Tax Cuts And Jobs Act Of 2017, Amount Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act of 2017, Amount Excess tax benefits on vesting of Restricted Stock Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit (Tax Shortfall), Amount Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit (Tax Shortfall), Amount Income tax benefit from dividends paid on Restricted Stock Effective Income Tax Rate Reconciliation, Deduction, Dividends, Amount Other Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Provision for income taxes Statement of Financial Position [Abstract] ASSETS Assets [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Investment portfolio Investments Accounts receivable Accounts Receivable, Net Prepaid expenses Prepaid Expense Income taxes receivable Income Taxes Receivable, Current Property and equipment, net of depreciation Property, Plant and Equipment, Net Deferred taxes Deferred Tax Assets, Net of Valuation Allowance Total assets Assets LIABILITIES AND SHAREHOLDERS’ EQUITY Liabilities and Equity [Abstract] Liabilities Liabilities [Abstract] Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities Accrued incentive compensation Accrued Bonuses, Current Deferred compensation Deferred Compensation Liability, Current and Noncurrent Total liabilities Liabilities Redeemable noncontrolling interest Redeemable Noncontrolling Interest, Equity, Common, Fair Value Permanent Shareholders’ Equity Stockholders' Equity Attributable to Parent [Abstract] Common stock, no par value 7,000,000 shares authorized; 3,470,428 issued and outstanding at December 31, 2017 (inclusive of 191,900 unvested shares); 3,411,556 issued and outstanding at December 31, 2016 (inclusive of 201,800 unvested shares) Common Stock, Value, Issued Preferred stock, undesignated, 1,000,000 shares authorized and unissued Preferred Stock, Value, Issued Deferred equity compensation Deferred Compensation Equity Retained Earnings Retained Earnings (Accumulated Deficit) Total permanent shareholders’ equity Total liabilities and shareholders’ equity Liabilities and Equity Book value per share Book Value Per Share Book value per share is computed by dividing total shareholders' equity by the number of shares issued and outstanding at the end of the measurement period. Fair Value Measurements, Recurring and Nonrecurring Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Assets under management (AUM) subject to variable fees and the variable fees Assets Under Management Variable Performance Fees [Table Text Block] Assets under management (AUM) subject to variable performance fees and variance performance fees. Mutual fund administration gross and net revenue Mutual Fund Administration Gross and Net Revenue [Table Text Block] Mutual fund administration gross and net revenue. Common Stock Shares Issued Equity Method Investments [Abstract] Equity Method Investments [Abstract] Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Research Opportunities Fund Research Opportunities Fund [Member] Research opportunities fund. High Yield Fund High Yield Fund [Member] High Yield Fund Global Fund LP Global Fund LP [Member] Global Fund LP International Equity Fund LP International Equity Fund LP [Member] International Equity Fund LP Mid Cap Fund Mid Cap Fund [Member] Mid Cap Fund [Member] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Equity Method Investment, Ownership Percentage Equity Method Investment, Ownership Percentage Retirement Plan Type [Axis] Retirement Plan Type [Axis] Retirement Plan Type [Domain] Retirement Plan Type [Domain] 401K Other Postretirement Benefits Plan [Member] Expenses attributable to the 401(k) Plan Allocated Share-based Compensation Expense Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Reclassification Reclassification, Policy [Policy Text Block] Principles of Consolidation Consolidation, Policy [Policy Text Block] Redeemable Noncontrolling Interest Consolidation, Subsidiaries or Other Investments, Consolidated Entities, Policy [Policy Text Block] Segment Information Segment Reporting, Policy [Policy Text Block] Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Accounts Receivable Receivables, Policy [Policy Text Block] Investments Investment, Policy [Policy Text Block] Fair Value Measurements Fair Value Measurement, Policy [Policy Text Block] Property and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Revenue Recognition - General Revenue Recognition, Policy [Policy Text Block] Revenue Recognition - Variable Fee Revenue Revenue Recognition, Services, Management Fees [Policy Text Block] Revenue Recognition - Mutual Fund Administration Revenue Recognition Accounting Policy, Gross and Net Revenue Disclosure [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Recently Issued Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Mutual fund administration gross and net revenue Mutual Fund Administration Gross and Net Revenue [Abstract] Mutual fund administration gross and net revenue. Mutual fund administration: Mutual Fund Administration [Abstract] Mutual fund administration. Administration revenue, gross Administrative Services Revenue 12b-1/service fees and commission revenue received from fund clients Fees and Commissions 12b-1/service fees and commission expense payments to third parties Service Fees and Commission Expense Payments to Third Parties Service fees and commission expense payments to third parties. Fund related expense Fund Related Expense Fund related expense. Revenue, net of fund related expenses Revenue from Administrative Services Excluding Financial Activity Net Revenue from administrative services excluding financial activity net. DHCM C-Share financing: Share Financing [Abstract] DHCM C-Share financing. Broker commission advance repayments Broker Commission Advance Repayments Broker commission advance repayments. Broker commission amortization Broker Commission Amortization Broker commission amortization. Financing activity, net Financing Activity Net Financing activity, net. Mutual fund administration revenue, net Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Investment Portfolio Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Debt Disclosure [Abstract] Line of Credit Debt Disclosure [Text Block] Line of Credit Facility [Table] Line of Credit Facility [Table] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] The Credit Agreement The Credit Agreement [Member] The Credit Agreement [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Line of Credit Line of Credit [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] London Interbank Offered Rate (LIBOR) London Interbank Offered Rate (LIBOR) [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Maximum borrowing amount Line of Credit Facility, Maximum Borrowing Capacity Line of credit facility, interest rate description Debt Instrument, Basis Spread on Variable Rate Borrowing under line of credit facility Long-term Line of Credit, Noncurrent Line of credit facility, unused capacity, commitment fee percentage Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Equity [Abstract] Common Stock, No Par Value (in dollars per share) Common Stock, No Par Value Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Earnings Per Share Earnings Per Share [Text Block] Common stock, shares authorized Common Stock, Shares Authorized Common stock, shares issued Common Stock, Shares, Issued Common stock, shares outstanding Common stock, unvested shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Preferred stock, shares authorized Preferred stock, shares issued Computation for earnings per share Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract] Net Income Less: Net income attributable to redeemable noncontrolling interest Weighted average number of outstanding shares Weighted average number of outstanding shares (in shares) Dilutive impact of restricted stock grants with forfeitable rights to dividends (in shares) Incremental Common Shares Attributable to Dilutive Effect of Nonvested Shares with Forfeitable Dividends Dilutive impact of restricted stock units (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Weighted average number of outstanding shares - Diluted (in shares) Earnings per share attributable to common shareholders Earnings Per Share, Basic and Diluted [Abstract] Summary of Deferred tax assets and liabilities Components of Deferred Tax Assets and Liabilities [Abstract] Stock-based compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost Accrued compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits Unrealized gains Deferred Tax Liabilities, Unrealized Gains on Trading Securities Property and equipment Deferred Tax Liabilities, Property, Plant and Equipment Other assets and liabilities Deferred Tax Assets (Liabilities) Other Deferred tax assets (liabilities) other. Net deferred tax assets Deferred Tax Assets, Net 2011 Equity and Cash Incentive Plan Equity and Cash Incentive Plan [Member] 2011 equity and cash incentive plan. Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Authorizes the issuance of Common Shares in various forms of equity awards Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Common Shares available for awards Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Deferred compensation equity Defined contribution plan, employer matching contribution, percent of match Defined Contribution Plan, Employer Matching Contribution, Percent of Match Employee's compensation contributed to the plan Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay Number of years of employment required to vest in contribution Defined Contribution Plan Number Years of Service of Employees Required Number years of service required of employees to vest in contribution. Deferred compensation arrangement, fully vested employee elected deferral period Deferred Compensation Arrangement, Fully Vested Employee Elected Deferral Period Deferred Compensation Arrangement, Fully Vested Employee Elected Deferral Period Deferred compensation liability, current and noncurrent Discontinued Operations and Disposal Groups [Abstract] Sale of Beacon Hill Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Computation for earnings per share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Statement of Cash Flows [Abstract] CASH FLOWS FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation Depreciation Share-based compensation Share-based Compensation Decrease (increase) in accounts receivable Increase (Decrease) in Accounts Receivable Change in current income taxes Increase (Decrease) in Income Taxes Payable Change in deferred income taxes Increase (Decrease) in Deferred Income Taxes Gain on sale of subsidiary Net (gains)/losses on investments Gain (Loss) on Investments Net change in trading securities held by Consolidated Funds Increase (Decrease) in Trading Securities Increase in accrued incentive compensation Increase (Decrease) in Employee Related Liabilities Increase in deferred compensation Increase (Decrease) in Deferred Compensation Excess income tax benefit from share-based compensation Excess Tax Benefit from Share-based Compensation, Operating Activities Income tax benefit from dividends paid on restricted stock Income Tax Benefit From Dividends Paid On Restricted Stock Operating Activities Income tax benefit from dividends paid on restricted stock. Other changes in assets and liabilities Increase (Decrease) in Other Operating Assets and Liabilities, Net Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities CASH FLOWS FROM INVESTING ACTIVITIES: Net Cash Provided by (Used in) Investing Activities [Abstract] Purchase of property and equipment Payments to Acquire Property, Plant, and Equipment Purchase of Company sponsored investments Payments to Acquire Investments Proceeds from sale of Company sponsored investments Proceeds from Sale, Maturity and Collection of Investments Proceeds from sale of subsidiary, net of cash disposed Proceeds from Divestiture of Businesses, Net of Cash Divested Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities CASH FLOWS FROM FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] Value of shares withheld related to employee tax withholding Payments Related to Tax Withholding for Share-based Compensation Excess income tax benefit from share-based compensation Excess Tax Benefit from Share-based Compensation, Financing Activities Income tax benefit from dividends paid on restricted stock Income Tax Benefit From Dividends Paid On Restricted Stock Financing Activities Income tax benefit from dividends paid on restricted stock. Payment of dividends Payments of Ordinary Dividends, Common Stock Net subscriptions received from redeemable noncontrolling interest holders Proceeds from (Payments to) Noncontrolling Interests Net cash used in financing activities Net Cash Provided by (Used in) Financing Activities CASH AND CASH EQUIVALENTS Cash and Cash Equivalents, at Carrying Value [Abstract] Net change during the year Cash and Cash Equivalents, Period Increase (Decrease) At beginning of year At end of year Supplemental cash flow information: Supplemental Cash Flow Information [Abstract] Income taxes paid Income Taxes Paid Supplemental disclosure of non-cash transactions: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Charitable donation of corporate investments and property and equipment Contribution of Investments and Property and Equipment Value of investments and property and equipment contributed in noncash investing and financing activities. Common stock issued as incentive compensation Cumulative-effect adjustment from the adoption of ASU 2015-02 (Note 2) New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification Net redemptions of ETF Shares for marketable securities Net issuance of ETF shares for marketable securities Value of ETF shares issued in exchange for marketable securities. Summary of total lease and operating expense Operating Leases, Rent Expense, Net [Abstract] Lease and operating expenses Operating Leases, Rent Expense, Net Document and Entity Information [Abstract] Document and Entity Information [Abstract] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers Entity Current Reporting Status Entity Current Reporting Status Entity Public Float Entity Public Float Income Taxes Income Tax Disclosure [Text Block] Operating Leases Leases of Lessee Disclosure [Text Block] Summary of total lease and operating expense Lessee, Operating Lease, Disclosure [Table Text Block] Future minimum lease payments under the operating leases Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Outstanding shares, Beginning Balance (in shares) Grants issued (in shares) Grants vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Grants forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Outstanding shares, Ending Balance (in shares) Weighted-Average Grant Date Price per Share Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] 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 Grants issued (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 Grants 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 Grants 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 End of the period (in dollars per share) Capital Stock Stockholders' Equity Note Disclosure [Text Block] Significant Accounting Policies Significant Accounting Policies [Text Block] Business Organization And Significant Accounting Policies [Table] Business Organization And Significant Accounting Policies [Table] Business Organization And Significant Accounting Policies [Table] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Affiliated Entity Affiliated Entity [Member] Related Party Transaction [Axis] Related Party Transaction [Axis] Related Party Transaction [Domain] Related Party Transaction [Domain] Investment Advisory And Fund Administration Services Investment Advisory And Fund Administration Services [Member] Investment Advisory And Fund Administration Services [Member] Mutual fund administrative services Mutual Fund Administrative Services [Member] Mutual fund administrative services [Member] Money Market Funds Money Market Funds [Member] Business Organization And Significant Accounting Policies [Line Items] Business Organization And Significant Accounting Policies [Line Items] Business Organization And Significant Accounting Policies [Line Items] Cumulative-effect adjustment from the adoption of ASU 2015-02 (Note 2) Number of business segment Number of Operating Segments Allowance for doubtful accounts Allowance for Doubtful Accounts Receivable Accounts receivable, related parties Accounts Receivable, Related Parties Transfers between fair value levels Fair Value, Transfers Between Level 1, Level 2, or Level 3, Amount Fair Value, Transfers Between Level 1, Level 2, or Level 3, Amount Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Revenue from related parties Revenue from Related Parties Rolling client investment performance period Rolling Client Investment Performance Period Rolling Client Investment Performance Period Performance fees Performance Fees Advance commissions amortization period Advance Commissions Amortization Period Advance commissions amortization period. Liability for uncertain tax positions, current Liability for Uncertainty in Income Taxes, Current Summary of market value of investments Summary Investment Holdings [Table Text Block] Equity Method Investments Equity Method Investments [Table Text Block] Summary of consolidated Federal income tax return Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Summary of reconciliation of income tax expense Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Summary of Deferred tax assets and liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Roll-forward of outstanding restricted stock grants issued Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block] Expense recognition of deferred compensation Schedule of Expense Recognition of Deferred Compensation Arrangement [Table Text Block] Schedule of expense recognition of deferred compensation arrangement. Schedule of Grants Issued and Grant Date Fair Value Schedule of Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Grant Date Intrinsic Value [Table Text Block] Summary of company expenses attributable to the 401(k) Plan Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block] Deferred tax assets, valuation allowance Deferred Tax Assets, Valuation Allowance Income tax benefit to shareholders equity Income Tax Effects Allocated Directly to Equity Principal Transaction Revenue [Table] Principal Transaction Revenue [Table] Principal Transaction Revenue, Description of Reporting Category [Axis] Principal Transaction Revenue, Description of Reporting Category [Axis] Name of Reporting Category [Domain] Name of Reporting Category [Domain] Quarter Ended December 31, 2018 Asset Under Management Contractual Period End Date [Member] Asset under management contractual period end date. Quarter Ended September 30, 2019 Asset Under Management Contractual Period End Date 2 [Member] Asset Under Management Contractual Period End Date 2 [Member] Quarter Ended March 31, 2020 Asset Under Management Contractual Period End Date 3 [Member] Asset Under Management Contractual Period End Date 3 [Member] Quarter Ended September 30, 2021 Asset Under Management Contractual Period End Date 4 [Member] Asset Under Management Contractual Period End Date 4 [Member] Total Asset Under Management Contractual Period End Total [Member] Asset Under Management Contractual Period End Total Principal Transaction Revenue [Line Items] Principal Transaction Revenue [Line Items] Assets under management (AUM) subject to variable fees and the variable fees Investment Advisory, Management and Administrative Fees [Abstract] AUM subject to variable rate fees Assets Under Management Variable Performance Fees Assets under management (AUM) subject to variable performance fees and variable performance fees. Unearned variable rate fees Potential Variable Fees Based Upon Current Investment Results Potential Variable Fees Based Upon Current Investment Results Investment Holdings [Table] Investment Holdings [Table] Company Sponsored Investments Total Investment Holdings [Line Items] Investment Holdings [Line Items] Company sponsored equity method investments Equity Method Investments Total Investment Portfolio Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Disposal Group, Disposed of by Sale, Not Discontinued Operations Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] Disposal Group Name [Axis] Disposal Group Name [Axis] Disposal Group Name [Domain] Disposal Group Name [Domain] Beacon Hill Beacon Hill [Member] Beacon Hill [Member] Promissory Note Promissory Note [Member] Promissory Note [Member] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Cash consideration received net of cash disposed Contingent consideration received Disposal Group, Including Discontinued Operation, Contingent Consideration Disposal Group, Including Discontinued Operation, Contingent Consideration Proceeds from collection of notes receivable Proceeds from Collection of Notes Receivable Notes receivable, current Notes, Loans and Financing Receivable, Gross, Current Summary of consolidated Federal income tax return Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] Current city income tax provision Current Local Tax Expense (Benefit) Current local tax expense (benefit). Current state income tax provision Current State Tax Expense (Benefit) Current state tax expense (benefit). Current federal income tax provision Current Federal Tax Expense (Benefit) Deferred federal income tax expense (benefit) Deferred Federal Income Tax Expense (Benefit)