XML 91 R77.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Subsequent Events (Details) $ in Millions | Oct. 31, 2018 USD ($) $ / unit | Oct. 31, 2018 GBP (£) $ / unit | Sep. 30, 2018 USD ($) | Sep. 30, 2018 GBP (£) | Aug. 28, 2018 $ / unit
--- | --- | --- | --- | --- | ---
Designated as Hedging Instrument | Forward contracts | Net Investment Hedging |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Derivative notional amount |  |  | $ 400.0 | £ 285,800,000 |
Designated as Hedging Instrument | Forward contracts | Net Investment Hedging | Minimum |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Derivative, option strike price (in dollars per unit) |  |  |  |  | 1.288
Designated as Hedging Instrument | Forward contracts | Net Investment Hedging | Maximum |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Derivative, option strike price (in dollars per unit) |  |  |  |  | 1.535
Unsecured Debt | Term Loan |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Principal amount at maturity | £ |  |  |  | 290,000,000 |
Additional borrowing amount | £ |  |  |  | £ 50,000,000.0 |
Subsequent Event | Designated as Hedging Instrument | Forward contracts | Net Investment Hedging |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Derivative notional amount | $ 450.0 | £ 325,300,000 |  |  |
Subsequent Event | Designated as Hedging Instrument | Forward contracts | Net Investment Hedging | Minimum |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Derivative, option strike price (in dollars per unit) | 1.318 | 1.318 |  |  |
Subsequent Event | Designated as Hedging Instrument | Forward contracts | Net Investment Hedging | Maximum |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Derivative, option strike price (in dollars per unit) | 1.448 | 1.448 |  |  |
Subsequent Event | Unsecured Debt | Term Loan |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Principal amount at maturity | $ | $ 450.0 |  |  |  |
Additional borrowing amount | $ | $ 75.0 |  |  |  |

X
- Definition Line of Credit Facility, Maximum Borrowing Capacity, Additional Amount + References No definition available. + Details
Name: | amg_LineofCreditFacilityMaximumBorrowingCapacityAdditionalAmount
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
Name: | invest_DerivativeNotionalAmount
Namespace Prefix: | invest_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400 + Details
Name: | us-gaap_DebtInstrumentFaceAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The strike price on the foreign currency option contract such as a put option or a call option. + References No definition available. + Details
Name: | us-gaap_DerivativeForeignCurrencyOptionStrikePrice
Namespace Prefix: | us-gaap_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | instant

X
- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeForwardMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_NetInvestmentHedgingMember
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: | us-gaap_LongtermDebtTypeAxis=us-gaap_UnsecuredDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=amg_SeniorUnsecuredTermLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |