XML 26 R73.htm IDEA: XBRL DOCUMENT v2.4.0.6

Forward Equity Sale Agreement (Details) (Amended and restated forward equity sale agreement, USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended	12 Months Ended
	Aug. 31, 2012	Dec. 31, 2012
Amended and restated forward equity sale agreement
Forward equity sale agreement
Value of common stock to sell under each agreement, maximum	$ 400.0
Notional amount sold		$ 147.2
Average share price (in dollars per share)		$ 121.37

X

- Details

Name:	amg_ForwardContractLineItems
Namespace Prefix:	amg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Represents the maximum value of common stock under each forward equity sale agreements to sell shares of the entity's common stock.

+ References

No definition available.

+ Details

Name:	amg_ForwardEquityContractsMaximumValuePerAgreement
Namespace Prefix:	amg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Represents the sum of common stock sold under the forward equity sale agreements.

+ References

No definition available.

+ Details

Name:	amg_ForwardEquityContractsSharesSoldAmount
Namespace Prefix:	amg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Represents the average share price of common stock sold under the forward equity sale agreements.

+ References

No definition available.

+ Details

Name:	amg_ForwardEquityContractsSharesSoldAverageSharePrice
Namespace Prefix:	amg_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration