Equity - Narrative Related to Share Based Compensation Award (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Class of Stock [Line Items]
Proceeds from Stock Options Exercised	$ 200,000	$ 1,900,000	$ 2,900,000
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options	600,000	2,100,000	3,400,000
Adjustments to Additional Paid in Capital, Share-based Compensation and Exercise of Stock Options	(41,000)	1,100,000	1,400,000
Stock Issued During Period, Shares, Other	604	842	649
Stock Issued During Period, Value, Other	$ 20,000	$ 26,000	$ 15,000
Number of Board of Directors	15agm_NumberOfBoardOfDirectors
Common Class C, Non-Voting [Member]
Class of Stock [Line Items]
Number of Board of Directors	5	7	4

Number of Board of Directors

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- Definition

Changes in additional paid in capital related to exercise of share-based payments awards (such as stock options) and the amount of recognized equity-based compensation during the period (such as nonvested shares).

+ References

No definition available.

+ Details

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- Definition

Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (j)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

The cash inflow associated with the amount received from holders exercising their stock options. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (j)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585

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- Definition

Number of shares of stock issued during the period that is attributable to transactions involving issuance of stock not separately disclosed.

+ References

No definition available.

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- Definition

Value of shares of stock issued during the period that is attributable to transactions involving issuance of stock not separately disclosed.

+ References

No definition available.

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