Accounting Policies Real Estate Owned (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounting Policies [Abstract]
Capitalized Costs on Real Estate Owned	$ 0	$ 0

Capitalized Costs on Real Estate Owned which include costs related to the production of saleable goods or crops that are realizeable net of any revenues received

No definition available.

Name:	agm_CapitalizedCostsOnRealEstateOwned
Namespace Prefix:	agm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant