XML 60 R47.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Fair Value Measurements - Investments Measured at Net Asset Value as Practical Expedient (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 | Dec. 31, 2017
NAV of investments at fair value |  |  |
Life of funds (in years) |  | 15 years |
Other Investments |  |  |
NAV of investments at fair value |  |  |
Fair Value | [1] | $ 179.9 | $ 165.0
Unfunded Commitments |  | 120.4 | 98.8
Other Investments | Controlling Interest |  |  |
NAV of investments at fair value |  |  |
Fair Value |  | 99.0 | 80.1
Private Equity Funds |  |  |
NAV of investments at fair value |  |  |
Fair Value | [2] | 171.7 | 156.1
Unfunded Commitments | [2] | 120.4 | 98.8
Other Funds |  |  |
NAV of investments at fair value |  |  |
Fair Value | [3] | 8.2 | 8.9
Unfunded Commitments | [3] | $ 0.0 | $ 0.0
[1] | Fair value attributable to the controlling interest was $80.1 million and $99.0 million as of December 31, 2017 and March 31, 2018, respectively.
[2] | The Company uses NAV as a practical expedient one quarter in arrears (adjusted for current period calls and distributions) to determine the fair value. These funds primarily invest in a broad range of private equity funds, as well as making direct investments. Distributions will be received as the underlying assets are liquidated over the life of the funds, which is generally up to 15 years.
[3] | These are multi-disciplinary funds that invest across various asset classes and strategies, including long/short equity, credit and real estate. Investments are generally redeemable on a daily, monthly or quarterly basis.

X
- Definition Fair Value, Investments, Entities That Calculate NAVs, Life of Fund + References No definition available. + Details
Name: | amg_FairValueInvestmentsEntitiesThatCalculateNAVsLifeofFund
Namespace Prefix: | amg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value of investment in certain entities that calculate net asset value per share. Includes, but is not limited to, by unit, membership interest, or other ownership interest. Investment includes, but is not limited to, investment in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds. Excludes measurement of net asset value as estimate of fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258 + Details
Name: | us-gaap_AlternativeInvestmentsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258 + Details
Name: | us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareUnfundedCommittments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_OtherThanSecuritiesInvestmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_ParentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_PrivateEquityFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=amg_OtherFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |