XML 64 R47.htm IDEA: XBRL DOCUMENT
v3.21.1

Fair Value Measurements - Quantitative Information used in Valuing Level 3 Liabilities (Details) - Significant Unobservable Inputs (Level 3) - Affiliate equity purchase obligations - Discounted cash flow $ in Millions | Mar. 31, 2021 USD ($) | Dec. 31, 2020 USD ($)
--- | --- | ---
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Fair Value | $ 66.1 | $ 22.0
Growth rates | Minimum |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Affiliate equity repurchase obligations, measurement input | (0.01) | (0.05)
Growth rates | Maximum |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Affiliate equity repurchase obligations, measurement input | 0.08 | 0.08
Growth rates | Weighted Average |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Affiliate equity repurchase obligations, measurement input | 0.04 | 0.03
Discount rates | Minimum |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Affiliate equity repurchase obligations, measurement input | 0.14 | 0.14
Discount rates | Maximum |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Affiliate equity repurchase obligations, measurement input | 0.16 | 0.16
Discount rates | Weighted Average |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Affiliate equity repurchase obligations, measurement input | 0.15 | 0.15

X
- Definition Obligations to Related Parties, Measurement Input + References No definition available. + Details
Name: | amg_ObligationstoRelatedPartiesMeasurementInput
Namespace Prefix: | amg_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value of financial and nonfinancial obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
Name: | us-gaap_LiabilitiesFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByLiabilityClassAxis=amg_ObligationsToRelatedPartiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=amg_DiscountedCashFlowValuationTechniqueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputLongTermRevenueGrowthRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |