XML 50 R38.htm IDEA: XBRL DOCUMENT
v3.4.0.3

Fair Value Measurements - Summary of Investments in Certain Entities that Calculate Net Asset Value (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2016 | Dec. 31, 2015
NAV of investments at fair value |  |  |
Fair value |  | $ 180.2 | $ 198.3
Unfunded commitments |  | $ 77.2 | 76.8
Life of funds (in years) |  | 15 years |
Private Equity Funds |  |  |
NAV of investments at fair value |  |  |
Fair value | [1] | $ 137.3 | 126.0
Unfunded commitments | [1] | 77.2 | 76.8
Other Funds |  |  |
NAV of investments at fair value |  |  |
Fair value | [2] | 42.9 | 72.3
Unfunded commitments | [2] | $ 0.0 | $ 0.0
[1] | These funds primarily invest in a broad range of private equity funds, as well as make 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.
[2] | 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 investments in certain entities that calculate net asset value per share, including, but not limited to, by unit, membership interest, or other ownership interest. Investments include, but are not limited to, investments in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 Reference 2: 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=36462937&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=36462937&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_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: |