3.25.0.1 html 326 557 1 false 108 0 false 8 false false R1.htm 0000001 - Document - Cover Page Sheet http://www.amg.com/role/CoverPage Cover Page Cover 1 false false R2.htm 0000002 - Document - Audit Information Sheet http://www.amg.com/role/AuditInformation Audit Information Cover 2 false false R3.htm 9952151 - Statement - CONSOLIDATED STATEMENTS OF INCOME Sheet http://www.amg.com/role/CONSOLIDATEDSTATEMENTSOFINCOME CONSOLIDATED STATEMENTS OF INCOME Statements 3 false false R4.htm 9952152 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME Sheet http://www.amg.com/role/CONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME Statements 4 false false R5.htm 9952153 - Statement - CONSOLIDATED BALANCE SHEETS Sheet http://www.amg.com/role/CONSOLIDATEDBALANCESHEETS CONSOLIDATED BALANCE SHEETS Statements 5 false false R6.htm 9952154 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical) Sheet http://www.amg.com/role/CONSOLIDATEDBALANCESHEETSParenthetical CONSOLIDATED BALANCE SHEETS (Parenthetical) Statements 6 false false R7.htm 9952155 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY Sheet http://www.amg.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINEQUITY CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY Statements 7 false false R8.htm 9952156 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Parenthetical) Sheet http://www.amg.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINEQUITYParenthetical CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Parenthetical) Statements 8 false false R9.htm 9952157 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS Sheet http://www.amg.com/role/CONSOLIDATEDSTATEMENTSOFCASHFLOWS CONSOLIDATED STATEMENTS OF CASH FLOWS Statements 9 false false R10.htm 9952158 - Disclosure - Business and Summary of Significant Accounting Policies Sheet http://www.amg.com/role/BusinessandSummaryofSignificantAccountingPolicies Business and Summary of Significant Accounting Policies Notes 10 false false R11.htm 9952159 - Disclosure - Investments Sheet http://www.amg.com/role/Investments Investments Notes 11 false false R12.htm 9952160 - Disclosure - Fair Value Measurements Sheet http://www.amg.com/role/FairValueMeasurements Fair Value Measurements Notes 12 false false R13.htm 9952161 - Disclosure - Investments in Affiliates and Affiliate Sponsored Investment Products Sheet http://www.amg.com/role/InvestmentsinAffiliatesandAffiliateSponsoredInvestmentProducts Investments in Affiliates and Affiliate Sponsored Investment Products Notes 13 false false R14.htm 9952162 - Disclosure - Debt Sheet http://www.amg.com/role/Debt Debt Notes 14 false false R15.htm 9952163 - Disclosure - Commitments and Contingencies Sheet http://www.amg.com/role/CommitmentsandContingencies Commitments and Contingencies Notes 15 false false R16.htm 9952164 - Disclosure - Goodwill and Acquired Client Relationships Sheet http://www.amg.com/role/GoodwillandAcquiredClientRelationships Goodwill and Acquired Client Relationships Notes 16 false false R17.htm 9952165 - Disclosure - Equity Method Investments in Affiliates Sheet http://www.amg.com/role/EquityMethodInvestmentsinAffiliates Equity Method Investments in Affiliates Notes 17 false false R18.htm 9952166 - Disclosure - Lease Commitments Sheet http://www.amg.com/role/LeaseCommitments Lease Commitments Notes 18 false false R19.htm 9952167 - Disclosure - Fixed Assets Sheet http://www.amg.com/role/FixedAssets Fixed Assets Notes 19 false false R20.htm 9952168 - Disclosure - Payables and Accrued Liabilities Sheet http://www.amg.com/role/PayablesandAccruedLiabilities Payables and Accrued Liabilities Notes 20 false false R21.htm 9952169 - Disclosure - Related Party Transactions Sheet http://www.amg.com/role/RelatedPartyTransactions Related Party Transactions Notes 21 false false R22.htm 9952170 - Disclosure - Stockholders' Equity Sheet http://www.amg.com/role/StockholdersEquity Stockholders' Equity Notes 22 false false R23.htm 9952171 - Disclosure - Share-Based Compensation Sheet http://www.amg.com/role/ShareBasedCompensation Share-Based Compensation Notes 23 false false R24.htm 9952172 - Disclosure - Redeemable Non-Controlling Interests Sheet http://www.amg.com/role/RedeemableNonControllingInterests Redeemable Non-Controlling Interests Notes 24 false false R25.htm 9952173 - Disclosure - Affiliate Equity Sheet http://www.amg.com/role/AffiliateEquity Affiliate Equity Notes 25 false false R26.htm 9952174 - Disclosure - Benefit Plans Sheet http://www.amg.com/role/BenefitPlans Benefit Plans Notes 26 false false R27.htm 9952175 - Disclosure - Income Taxes Sheet http://www.amg.com/role/IncomeTaxes Income Taxes Notes 27 false false R28.htm 9952176 - Disclosure - Earnings Per Share Sheet http://www.amg.com/role/EarningsPerShare Earnings Per Share Notes 28 false false R29.htm 9952177 - Disclosure - Comprehensive Income Sheet http://www.amg.com/role/ComprehensiveIncome Comprehensive Income Notes 29 false false R30.htm 9952178 - Disclosure - Segment and Geographic Information Sheet http://www.amg.com/role/SegmentandGeographicInformation Segment and Geographic Information Notes 30 false false R31.htm 9952179 - Disclosure - Schedule II - Valuation and Qualifying Accounts Sheet http://www.amg.com/role/ScheduleIIValuationandQualifyingAccounts Schedule II - Valuation and Qualifying Accounts Notes 31 false false R32.htm 995410 - Disclosure - Pay vs Performance Disclosure Sheet http://xbrl.sec.gov/ecd/role/PvpDisclosure Pay vs Performance Disclosure Notes 32 false false R33.htm 995445 - Disclosure - Insider Trading Arrangements Sheet http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements Insider Trading Arrangements Notes 33 false false R34.htm 995447 - Disclosure - Insider Trading Policies and Procedures Sheet http://xbrl.sec.gov/ecd/role/InsiderTradingPoliciesProc Insider Trading Policies and Procedures Notes 34 false false R35.htm 995550 - Disclosure - Cybersecurity Risk Management and Strategy Disclosure Sheet http://xbrl.sec.gov/cyd/role/CybersecurityRiskManagementAndStrategyDisclosure Cybersecurity Risk Management and Strategy Disclosure Notes 35 false false R36.htm 9955511 - Disclosure - Business and Summary of Significant Accounting Policies (Policies) Sheet http://www.amg.com/role/BusinessandSummaryofSignificantAccountingPoliciesPolicies Business and Summary of Significant Accounting Policies (Policies) Policies http://www.amg.com/role/BusinessandSummaryofSignificantAccountingPolicies 36 false false R37.htm 9955512 - Disclosure - Investments (Tables) Sheet http://www.amg.com/role/InvestmentsTables Investments (Tables) Tables http://www.amg.com/role/Investments 37 false false R38.htm 9955513 - Disclosure - Fair Value Measurements (Tables) Sheet http://www.amg.com/role/FairValueMeasurementsTables Fair Value Measurements (Tables) Tables http://www.amg.com/role/FairValueMeasurements 38 false false R39.htm 9955514 - Disclosure - Investments in Affiliates and Affiliate Sponsored Investment Products (Tables) Sheet http://www.amg.com/role/InvestmentsinAffiliatesandAffiliateSponsoredInvestmentProductsTables Investments in Affiliates and Affiliate Sponsored Investment Products (Tables) Tables http://www.amg.com/role/InvestmentsinAffiliatesandAffiliateSponsoredInvestmentProducts 39 false false R40.htm 9955515 - Disclosure - Debt (Tables) Sheet http://www.amg.com/role/DebtTables Debt (Tables) Tables http://www.amg.com/role/Debt 40 false false R41.htm 9955516 - Disclosure - Goodwill and Acquired Client Relationships (Tables) Sheet http://www.amg.com/role/GoodwillandAcquiredClientRelationshipsTables Goodwill and Acquired Client Relationships (Tables) Tables http://www.amg.com/role/GoodwillandAcquiredClientRelationships 41 false false R42.htm 9955517 - Disclosure - Equity Method Investments in Affiliates (Tables) Sheet http://www.amg.com/role/EquityMethodInvestmentsinAffiliatesTables Equity Method Investments in Affiliates (Tables) Tables http://www.amg.com/role/EquityMethodInvestmentsinAffiliates 42 false false R43.htm 9955518 - Disclosure - Lease Commitments (Tables) Sheet http://www.amg.com/role/LeaseCommitmentsTables Lease Commitments (Tables) Tables http://www.amg.com/role/LeaseCommitments 43 false false R44.htm 9955519 - Disclosure - Fixed Assets (Tables) Sheet http://www.amg.com/role/FixedAssetsTables Fixed Assets (Tables) Tables http://www.amg.com/role/FixedAssets 44 false false R45.htm 9955520 - Disclosure - Payables and Accrued Liabilities (Tables) Sheet http://www.amg.com/role/PayablesandAccruedLiabilitiesTables Payables and Accrued Liabilities (Tables) Tables http://www.amg.com/role/PayablesandAccruedLiabilities 45 false false R46.htm 9955521 - Disclosure - Stockholders' Equity (Tables) Sheet http://www.amg.com/role/StockholdersEquityTables Stockholders' Equity (Tables) Tables http://www.amg.com/role/StockholdersEquity 46 false false R47.htm 9955522 - Disclosure - Share-Based Compensation (Tables) Sheet http://www.amg.com/role/ShareBasedCompensationTables Share-Based Compensation (Tables) Tables http://www.amg.com/role/ShareBasedCompensation 47 false false R48.htm 9955523 - Disclosure - Redeemable Non-Controlling Interests (Tables) Sheet http://www.amg.com/role/RedeemableNonControllingInterestsTables Redeemable Non-Controlling Interests (Tables) Tables http://www.amg.com/role/RedeemableNonControllingInterests 48 false false R49.htm 9955524 - Disclosure - Affiliate Equity (Tables) Sheet http://www.amg.com/role/AffiliateEquityTables Affiliate Equity (Tables) Tables http://www.amg.com/role/AffiliateEquity 49 false false R50.htm 9955525 - Disclosure - Income Taxes (Tables) Sheet http://www.amg.com/role/IncomeTaxesTables Income Taxes (Tables) Tables http://www.amg.com/role/IncomeTaxes 50 false false R51.htm 9955526 - Disclosure - Earnings Per Share (Tables) Sheet http://www.amg.com/role/EarningsPerShareTables Earnings Per Share (Tables) Tables http://www.amg.com/role/EarningsPerShare 51 false false R52.htm 9955527 - Disclosure - Comprehensive Income (Tables) Sheet http://www.amg.com/role/ComprehensiveIncomeTables Comprehensive Income (Tables) Tables http://www.amg.com/role/ComprehensiveIncome 52 false false R53.htm 9955528 - Disclosure - Segment and Geographic Information (Tables) Sheet http://www.amg.com/role/SegmentandGeographicInformationTables Segment and Geographic Information (Tables) Tables http://www.amg.com/role/SegmentandGeographicInformation 53 false false R54.htm 9955529 - Disclosure - Business and Summary of Significant Accounting Policies (Details) Sheet http://www.amg.com/role/BusinessandSummaryofSignificantAccountingPoliciesDetails Business and Summary of Significant Accounting Policies (Details) Details http://www.amg.com/role/BusinessandSummaryofSignificantAccountingPoliciesPolicies 54 false false R55.htm 9955530 - Disclosure - Investments - Schedule of Investments in Marketable Securities and Other Investments (Details) Sheet http://www.amg.com/role/InvestmentsScheduleofInvestmentsinMarketableSecuritiesandOtherInvestmentsDetails Investments - Schedule of Investments in Marketable Securities and Other Investments (Details) Details 55 false false R56.htm 9955531 - Disclosure - Investments - Cost, Gross Unrealized Gains and Losses and Fair Value (Details) Sheet http://www.amg.com/role/InvestmentsCostGrossUnrealizedGainsandLossesandFairValueDetails Investments - Cost, Gross Unrealized Gains and Losses and Fair Value (Details) Details 56 false false R57.htm 9955532 - Disclosure - Investments - Additional Information (Details) Sheet http://www.amg.com/role/InvestmentsAdditionalInformationDetails Investments - Additional Information (Details) Details 57 false false R58.htm 9955533 - Disclosure - Investments - Debt Securities, Available-for-Sale (Details) Sheet http://www.amg.com/role/InvestmentsDebtSecuritiesAvailableforSaleDetails Investments - Debt Securities, Available-for-Sale (Details) Details 58 false false R59.htm 9955534 - Disclosure - Investments - Investments Measured at NAV as a Practical Expedient (Details) Sheet http://www.amg.com/role/InvestmentsInvestmentsMeasuredatNAVasaPracticalExpedientDetails Investments - Investments Measured at NAV as a Practical Expedient (Details) Details 59 false false R60.htm 9955535 - Disclosure - Investments - Investments without Readily Determinable Fair Value (Details) Sheet http://www.amg.com/role/InvestmentsInvestmentswithoutReadilyDeterminableFairValueDetails Investments - Investments without Readily Determinable Fair Value (Details) Details 60 false false R61.htm 9955536 - Disclosure - Investments - Schedule of Changes in Other Investments (Details) Sheet http://www.amg.com/role/InvestmentsScheduleofChangesinOtherInvestmentsDetails Investments - Schedule of Changes in Other Investments (Details) Details 61 false false R62.htm 9955537 - Disclosure - Fair Value Measurements - Assets and Liabilities Measured on a Recurring Basis (Details) Sheet http://www.amg.com/role/FairValueMeasurementsAssetsandLiabilitiesMeasuredonaRecurringBasisDetails Fair Value Measurements - Assets and Liabilities Measured on a Recurring Basis (Details) Details 62 false false R63.htm 9955538 - Disclosure - Fair Value Measurements - Changes in Level 3 Liabilities (Details) Sheet http://www.amg.com/role/FairValueMeasurementsChangesinLevel3LiabilitiesDetails Fair Value Measurements - Changes in Level 3 Liabilities (Details) Details 63 false false R64.htm 9955539 - Disclosure - Fair Value Measurements - Quantitative Information used in Valuing Level 3 Liabilities (Details) Sheet http://www.amg.com/role/FairValueMeasurementsQuantitativeInformationusedinValuingLevel3LiabilitiesDetails Fair Value Measurements - Quantitative Information used in Valuing Level 3 Liabilities (Details) Details 64 false false R65.htm 9955540 - Disclosure - Fair Value Measurements - Other Financial Liabilities Not Carried at Fair Value (Details) Sheet http://www.amg.com/role/FairValueMeasurementsOtherFinancialLiabilitiesNotCarriedatFairValueDetails Fair Value Measurements - Other Financial Liabilities Not Carried at Fair Value (Details) Details 65 false false R66.htm 9955541 - Disclosure - Investments in Affiliates and Affiliate Sponsored Investment Products - Affiliated Accounted For Under Equity Method (Details) Sheet http://www.amg.com/role/InvestmentsinAffiliatesandAffiliateSponsoredInvestmentProductsAffiliatedAccountedForUnderEquityMethodDetails Investments in Affiliates and Affiliate Sponsored Investment Products - Affiliated Accounted For Under Equity Method (Details) Details 66 false false R67.htm 9955542 - Disclosure - Investments in Affiliates and Affiliate Sponsored Investment Products - Affiliated Sponsored Investment Products (Details) Sheet http://www.amg.com/role/InvestmentsinAffiliatesandAffiliateSponsoredInvestmentProductsAffiliatedSponsoredInvestmentProductsDetails Investments in Affiliates and Affiliate Sponsored Investment Products - Affiliated Sponsored Investment Products (Details) Details 67 false false R68.htm 9955543 - Disclosure - Debt - Schedule of Debt (Details) Sheet http://www.amg.com/role/DebtScheduleofDebtDetails Debt - Schedule of Debt (Details) Details 68 false false R69.htm 9955544 - Disclosure - Debt - Additional Information (Details) Sheet http://www.amg.com/role/DebtAdditionalInformationDetails Debt - Additional Information (Details) Details 69 false false R70.htm 9955545 - Disclosure - Debt - Principal Terms of Senior and Junior Subordinated Notes (Details) Notes http://www.amg.com/role/DebtPrincipalTermsofSeniorandJuniorSubordinatedNotesDetails Debt - Principal Terms of Senior and Junior Subordinated Notes (Details) Details 70 false false R71.htm 9955546 - Disclosure - Debt - Schedule of Convertible Securities (Details) Sheet http://www.amg.com/role/DebtScheduleofConvertibleSecuritiesDetails Debt - Schedule of Convertible Securities (Details) Details 71 false false R72.htm 9955547 - Disclosure - Commitments and Contingencies - Additional Information (Details) Sheet http://www.amg.com/role/CommitmentsandContingenciesAdditionalInformationDetails Commitments and Contingencies - Additional Information (Details) Details 72 false false R73.htm 9955548 - Disclosure - Goodwill and Acquired Client Relationships - Schedule of Changes in Goodwill (Details) Sheet http://www.amg.com/role/GoodwillandAcquiredClientRelationshipsScheduleofChangesinGoodwillDetails Goodwill and Acquired Client Relationships - Schedule of Changes in Goodwill (Details) Details 73 false false R74.htm 9955549 - Disclosure - Goodwill and Acquired Client Relationships - Additional Information (Details) Sheet http://www.amg.com/role/GoodwillandAcquiredClientRelationshipsAdditionalInformationDetails Goodwill and Acquired Client Relationships - Additional Information (Details) Details 74 false false R75.htm 9955550 - Disclosure - Goodwill and Acquired Client Relationships - Schedule of Changes in Acquired Client Relationships (Details) Sheet http://www.amg.com/role/GoodwillandAcquiredClientRelationshipsScheduleofChangesinAcquiredClientRelationshipsDetails Goodwill and Acquired Client Relationships - Schedule of Changes in Acquired Client Relationships (Details) Details 75 false false R76.htm 9955551 - Disclosure - Equity Method Investments in Affiliates - Schedule of Equity Method Investments in Affiliates (Details) Sheet http://www.amg.com/role/EquityMethodInvestmentsinAffiliatesScheduleofEquityMethodInvestmentsinAffiliatesDetails Equity Method Investments in Affiliates - Schedule of Equity Method Investments in Affiliates (Details) Details 76 false false R77.htm 9955552 - Disclosure - Equity Method Investments in Affiliates - Change in Equity Method Investments in Affiliates (Details) Sheet http://www.amg.com/role/EquityMethodInvestmentsinAffiliatesChangeinEquityMethodInvestmentsinAffiliatesDetails Equity Method Investments in Affiliates - Change in Equity Method Investments in Affiliates (Details) Details 77 false false R78.htm 9955553 - Disclosure - Equity Method Investments in Affiliates - Additional Information (Details) Sheet http://www.amg.com/role/EquityMethodInvestmentsinAffiliatesAdditionalInformationDetails Equity Method Investments in Affiliates - Additional Information (Details) Details 78 false false R79.htm 9955554 - Disclosure - Equity Method Investments in Affiliates - Financial Information for Affiliates Accounted for Under the Equity Method (Details) Sheet http://www.amg.com/role/EquityMethodInvestmentsinAffiliatesFinancialInformationforAffiliatesAccountedforUndertheEquityMethodDetails Equity Method Investments in Affiliates - Financial Information for Affiliates Accounted for Under the Equity Method (Details) Details 79 false false R80.htm 9955555 - Disclosure - Lease Commitments - Total Lease Costs (Net) (Details) Sheet http://www.amg.com/role/LeaseCommitmentsTotalLeaseCostsNetDetails Lease Commitments - Total Lease Costs (Net) (Details) Details 80 false false R81.htm 9955556 - Disclosure - Lease Commitments - Additional Information (Details) Sheet http://www.amg.com/role/LeaseCommitmentsAdditionalInformationDetails Lease Commitments - Additional Information (Details) Details 81 false false R82.htm 9955557 - Disclosure - Lease Commitments - Maturity of Lease Liabilities (Details) Sheet http://www.amg.com/role/LeaseCommitmentsMaturityofLeaseLiabilitiesDetails Lease Commitments - Maturity of Lease Liabilities (Details) Details 82 false false R83.htm 9955558 - Disclosure - Fixed Assets (Details) Sheet http://www.amg.com/role/FixedAssetsDetails Fixed Assets (Details) Details http://www.amg.com/role/FixedAssetsTables 83 false false R84.htm 9955559 - Disclosure - Payables and Accrued Liabilities (Details) Sheet http://www.amg.com/role/PayablesandAccruedLiabilitiesDetails Payables and Accrued Liabilities (Details) Details http://www.amg.com/role/PayablesandAccruedLiabilitiesTables 84 false false R85.htm 9955560 - Disclosure - Related Party Transactions (Details) Sheet http://www.amg.com/role/RelatedPartyTransactionsDetails Related Party Transactions (Details) Details http://www.amg.com/role/RelatedPartyTransactions 85 false false R86.htm 9955561 - Disclosure - Stockholders' Equity - Additional Information (Details) Sheet http://www.amg.com/role/StockholdersEquityAdditionalInformationDetails Stockholders' Equity - Additional Information (Details) Details 86 false false R87.htm 9955562 - Disclosure - Stockholders' Equity - Share Repurchase Activity (Details) Sheet http://www.amg.com/role/StockholdersEquityShareRepurchaseActivityDetails Stockholders' Equity - Share Repurchase Activity (Details) Details 87 false false R88.htm 9955563 - Disclosure - Share-Based Compensation - Share-Based Compensation Expense (Details) Sheet http://www.amg.com/role/ShareBasedCompensationShareBasedCompensationExpenseDetails Share-Based Compensation - Share-Based Compensation Expense (Details) Details 88 false false R89.htm 9955564 - Disclosure - Share-Based Compensation - Restricted Stock Units Transactions (Details) Sheet http://www.amg.com/role/ShareBasedCompensationRestrictedStockUnitsTransactionsDetails Share-Based Compensation - Restricted Stock Units Transactions (Details) Details 89 false false R90.htm 9955565 - Disclosure - Share-Based Compensation - Schedule of the Transactions of the Company's Stock Options (Details) Sheet http://www.amg.com/role/ShareBasedCompensationScheduleoftheTransactionsoftheCompanysStockOptionsDetails Share-Based Compensation - Schedule of the Transactions of the Company's Stock Options (Details) Details 90 false false R91.htm 9955566 - Disclosure - Share-Based Compensation - Fair Value Options Granted and Assumptions (Details) Sheet http://www.amg.com/role/ShareBasedCompensationFairValueOptionsGrantedandAssumptionsDetails Share-Based Compensation - Fair Value Options Granted and Assumptions (Details) Details 91 false false R92.htm 9955567 - Disclosure - Redeemable Non-Controlling Interests (Details) Sheet http://www.amg.com/role/RedeemableNonControllingInterestsDetails Redeemable Non-Controlling Interests (Details) Details http://www.amg.com/role/RedeemableNonControllingInterestsTables 92 false false R93.htm 9955568 - Disclosure - Affiliate Equity - Additional Information (Details) Sheet http://www.amg.com/role/AffiliateEquityAdditionalInformationDetails Affiliate Equity - Additional Information (Details) Details 93 false false R94.htm 9955569 - Disclosure - Affiliate Equity - Summary of Affiliate Recognized and Unrecognized Expense (Details) Sheet http://www.amg.com/role/AffiliateEquitySummaryofAffiliateRecognizedandUnrecognizedExpenseDetails Affiliate Equity - Summary of Affiliate Recognized and Unrecognized Expense (Details) Details 94 false false R95.htm 9955570 - Disclosure - Affiliate Equity - Changes in the Company's Interest in its Affiliates on the Controlling Interest's Equity (Details) Sheet http://www.amg.com/role/AffiliateEquityChangesintheCompanysInterestinitsAffiliatesontheControllingInterestsEquityDetails Affiliate Equity - Changes in the Company's Interest in its Affiliates on the Controlling Interest's Equity (Details) Details 95 false false R96.htm 9955571 - Disclosure - Benefit Plans (Details) Sheet http://www.amg.com/role/BenefitPlansDetails Benefit Plans (Details) Details http://www.amg.com/role/BenefitPlans 96 false false R97.htm 9955572 - Disclosure - Income Taxes - Schedule of Income Tax Provisions by Controlling and Noncontrolling Interests (Details) Sheet http://www.amg.com/role/IncomeTaxesScheduleofIncomeTaxProvisionsbyControllingandNoncontrollingInterestsDetails Income Taxes - Schedule of Income Tax Provisions by Controlling and Noncontrolling Interests (Details) Details 97 false false R98.htm 9955573 - Disclosure - Income Taxes - Schedule of Components of Consolidated Provision for Income Taxes (Details) Sheet http://www.amg.com/role/IncomeTaxesScheduleofComponentsofConsolidatedProvisionforIncomeTaxesDetails Income Taxes - Schedule of Components of Consolidated Provision for Income Taxes (Details) Details 98 false false R99.htm 9955574 - Disclosure - Income Taxes - Components of Income Before Income Taxes (Details) Sheet http://www.amg.com/role/IncomeTaxesComponentsofIncomeBeforeIncomeTaxesDetails Income Taxes - Components of Income Before Income Taxes (Details) Details 99 false false R100.htm 9955575 - Disclosure - Income Taxes - Reconciliation of U.S. Federal Statutory Tax Rate to Company's Effective Tax Rate (Details) Sheet http://www.amg.com/role/IncomeTaxesReconciliationofUSFederalStatutoryTaxRatetoCompanysEffectiveTaxRateDetails Income Taxes - Reconciliation of U.S. Federal Statutory Tax Rate to Company's Effective Tax Rate (Details) Details 100 false false R101.htm 9955576 - Disclosure - Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) Sheet http://www.amg.com/role/IncomeTaxesComponentsofDeferredTaxAssetsandLiabilitiesDetails Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) Details 101 false false R102.htm 9955577 - Disclosure - Income Taxes - Additional Information (Details) Sheet http://www.amg.com/role/IncomeTaxesAdditionalInformationDetails Income Taxes - Additional Information (Details) Details 102 false false R103.htm 9955578 - Disclosure - Income Taxes - Changes in Unrecognized Tax Benefits (Details) Sheet http://www.amg.com/role/IncomeTaxesChangesinUnrecognizedTaxBenefitsDetails Income Taxes - Changes in Unrecognized Tax Benefits (Details) Details 103 false false R104.htm 9955579 - Disclosure - Earnings Per Share - Schedule of Basic and Diluted Earnings (Loss) Per Share (Details) Sheet http://www.amg.com/role/EarningsPerShareScheduleofBasicandDilutedEarningsLossPerShareDetails Earnings Per Share - Schedule of Basic and Diluted Earnings (Loss) Per Share (Details) Details 104 false false R105.htm 9955580 - Disclosure - Earnings Per Share - Schedule of Shares Excluded from Calculation of Basic and Diluted Earnings (Loss) Per Share (Details) Sheet http://www.amg.com/role/EarningsPerShareScheduleofSharesExcludedfromCalculationofBasicandDilutedEarningsLossPerShareDetails Earnings Per Share - Schedule of Shares Excluded from Calculation of Basic and Diluted Earnings (Loss) Per Share (Details) Details 105 false false R106.htm 9955581 - Disclosure - Comprehensive Income - Summary of the Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Details) Sheet http://www.amg.com/role/ComprehensiveIncomeSummaryoftheTaxEffectsAllocatedtoEachComponentofOtherComprehensiveIncomeLossDetails Comprehensive Income - Summary of the Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Details) Details 106 false false R107.htm 9955582 - Disclosure - Comprehensive Income - Components of AOCL (Details) Sheet http://www.amg.com/role/ComprehensiveIncomeComponentsofAOCLDetails Comprehensive Income - Components of AOCL (Details) Details 107 false false R108.htm 9955583 - Disclosure - Segment and Geographic Information - Narrative (Details) Sheet http://www.amg.com/role/SegmentandGeographicInformationNarrativeDetails Segment and Geographic Information - Narrative (Details) Details 108 false false R109.htm 9955584 - Disclosure - Segment and Geographic Information (Details) Sheet http://www.amg.com/role/SegmentandGeographicInformationDetails Segment and Geographic Information (Details) Details http://www.amg.com/role/SegmentandGeographicInformationTables 109 false false R110.htm 9955585 - Disclosure - Schedule II - Valuation and Qualifying Accounts (Details) Sheet http://www.amg.com/role/ScheduleIIValuationandQualifyingAccountsDetails Schedule II - Valuation and Qualifying Accounts (Details) Details http://www.amg.com/role/ScheduleIIValuationandQualifyingAccounts 110 false false All Reports Book All Reports amg-20241231.htm amg-20241231.xsd amg-20241231_cal.xml amg-20241231_def.xml amg-20241231_lab.xml amg-20241231_pre.xml amg-20241231_g1.gif amg-20241231_g2.jpg http://fasb.org/srt/2024 http://fasb.org/us-gaap/2024 http://xbrl.sec.gov/cyd/2024 http://xbrl.sec.gov/dei/2024 http://xbrl.sec.gov/ecd/2024 true true