XML 23 R78.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Business Combinations - Schedule of Goodwill Allocation by Segment (Details) | Dec. 31, 2014
--- | ---
SouthernSun | Institutional |
Business Acquisition |
Goodwill allocation to business segments (percent) | 37.00%us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount / us-gaap_BusinessAcquisitionAxis = amg_SouthernSunMember / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember
SouthernSun | Mutual Fund |
Business Acquisition |
Goodwill allocation to business segments (percent) | 23.00%us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount / us-gaap_BusinessAcquisitionAxis = amg_SouthernSunMember / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember
SouthernSun | High Net Worth |
Business Acquisition |
Goodwill allocation to business segments (percent) | 40.00%us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount / us-gaap_BusinessAcquisitionAxis = amg_SouthernSunMember / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember
River Road | Institutional |
Business Acquisition |
Goodwill allocation to business segments (percent) | 31.00%us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount / us-gaap_BusinessAcquisitionAxis = amg_RiverRoadMember / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember
River Road | Mutual Fund |
Business Acquisition |
Goodwill allocation to business segments (percent) | 51.00%us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount / us-gaap_BusinessAcquisitionAxis = amg_RiverRoadMember / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember
River Road | High Net Worth |
Business Acquisition |
Goodwill allocation to business segments (percent) | 18.00%us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount / us-gaap_BusinessAcquisitionAxis = amg_RiverRoadMember / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember
Veritas | Institutional |
Business Acquisition |
Goodwill allocation to business segments (percent) | 24.00%us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount / us-gaap_BusinessAcquisitionAxis = amg_VeritasMember / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember
Veritas | Mutual Fund |
Business Acquisition |
Goodwill allocation to business segments (percent) | 76.00%us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount / us-gaap_BusinessAcquisitionAxis = amg_VeritasMember / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember
Veritas | High Net Worth |
Business Acquisition |
Goodwill allocation to business segments (percent) | 0.00%us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount / us-gaap_BusinessAcquisitionAxis = amg_VeritasMember / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember

X
- Details
Name: | us-gaap_BusinessAcquisitionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of fair value of reporting unit in excess of carrying amount. + References No definition available. + Details
Name: | us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=amg_RiverRoadMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=amg_SouthernSunMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=amg_VeritasMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |