XML 99 R77.htm IDEA: XBRL DOCUMENT
v3.20.4

Lease Commitments - Additional Information (Details) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Leases [Abstract] |  |  |  |
Consolidated rent expense |  |  |  | $ 40,500,000
Right-of-use assets obtained in exchange for new operating leases after adoption of ASC 842 |  | $ 24,400,000 | $ 26,100,000 |
Weighted average remaining lease term - operating leases | 8 years | 7 years | 8 years |
Weighted average discount rate - operating leases | 4.00% | 4.00% | 4.00% |
Expense recorded to reduce carrying value of right-of-use assets to fair value | $ 8,100,000 | $ 0 |  |
Level 3 | Discounted Cash Flow | Price per square foot | Minimum |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |
Right-of-use assets, measurement input | 13 |  |  |
Level 3 | Discounted Cash Flow | Price per square foot | Maximum |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |
Right-of-use assets, measurement input | 68 |  |  |
Level 3 | Discounted Cash Flow | Price per square foot | Weighted Average |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |
Right-of-use assets, measurement input | 46 |  |  |
Level 3 | Discounted Cash Flow | Discount rate | Minimum |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |
Right-of-use assets, measurement input | 0.033 |  |  |
Level 3 | Discounted Cash Flow | Discount rate | Maximum |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |
Right-of-use assets, measurement input | 0.055 |  |  |
Level 3 | Discounted Cash Flow | Tax rate |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |
Right-of-use assets, measurement input | 0.25 |  |  |

X
- Definition Right-of-Use Asset, Measurement Input + References No definition available. + Details
Name: | amg_RightofUseAssetMeasurementInput
Namespace Prefix: | amg_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration

X
- Definition Right-of-Use Asset Obtained in Exchange for Operating Lease Liability, After Adoption + References No definition available. + Details
Name: | amg_RightofUseAssetObtainedinExchangeforOperatingLeaseLiabilityAfterAdoption
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_LeasesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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_LesseeLeaseDescriptionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of loss from impairment of right-of-use asset from operating lease. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 25 -Paragraph 6 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121593497&loc=SL77918431-209957 + Details
Name: | us-gaap_OperatingLeaseImpairmentLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Weighted average discount rate for operating lease calculated at point in time. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (g)(4) -URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 55 -Paragraph 53 -URI http://asc.fasb.org/extlink&oid=121568110&loc=SL77918982-209971 + Details
Name: | us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Weighted average remaining lease term for operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 55 -Paragraph 53 -URI http://asc.fasb.org/extlink&oid=121568110&loc=SL77918982-209971 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (g)(3) -URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980 + Details
Name: | us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | instant

X
- Definition Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income. + References Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121573735&loc=d3e41499-112717 + Details
Name: | us-gaap_OperatingLeasesRentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

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

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=amg_MeasurementInputPricePerSquareFootMember
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: |

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