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Investment Securities - Schedule of Investment Securities (Details) (USD $)
In Thousands, unless otherwise specified
 0 Months Ended
Mar. 30, 2015
Dec. 31, 2014
Mar. 31, 2015
Available-for-sale Securities [Abstract]      
Derivative, Notional Amount   $ 6,837,571invest_DerivativeNotionalAmount $ 7,370,529invest_DerivativeNotionalAmount
Investment Securities [Member]      
Available-for-sale Securities [Abstract]      
Available-for-Sale Securities Unpaid Principal Balance   1,932,236agm_AvailableforSaleSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 2,135,218agm_AvailableforSaleSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
Unamortized Premium/(Discount)   7,471us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 6,966us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
Available-for-sale Securities, Amortized Cost Basis   1,939,707us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 2,142,184us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax   9,003us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 8,606us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
Available-for-sale Securities, Unrealized Losses   (10,211)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 (11,246)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
Available-for-sale Securities, Fair Value Disclosure   1,938,499us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 2,139,544us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
Trading Securities [Abstract]      
Trading, at fair value   689us-gaap_TradingSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 638us-gaap_TradingSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
Marketable Securities [Abstract]      
Marketable Securities Unpaid Principal Balance   1,935,104agm_MarketableSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 2,137,839agm_MarketableSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
Marketable Securities, Amortized Cost   1,942,575agm_MarketableSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 2,144,805agm_MarketableSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
Marketable Securities, Unrealized Gains   9,003agm_MarketableSecuritiesGrossUnrealizedGains
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 8,606agm_MarketableSecuritiesGrossUnrealizedGains
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
Marketable Securities, Unrealized Losses   (12,390)agm_MarketableSecuritiesGrossUnrealizedLosses
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 (13,229)agm_MarketableSecuritiesGrossUnrealizedLosses
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
Marketable Securities   1,939,188us-gaap_MarketableSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 2,140,182us-gaap_MarketableSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
USDA Securities [Member]
      
Available-for-sale Securities [Abstract]      
Available-for-sale Securities, Fair Value Disclosure   1,731,222us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember		 1,794,844us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Trading Securities [Abstract]      
Trading, at fair value   40,310us-gaap_TradingSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember		 37,593us-gaap_TradingSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Marketable Securities [Abstract]      
Marketable Securities   1,771,532us-gaap_MarketableSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember		 1,832,437us-gaap_MarketableSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Available-for-sale Securities [Member] | Investment Securities [Member]      
Available-for-sale Securities [Abstract]      
Unamortized Premium/(Discount)   7,471us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 6,966us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
Floating Interest Rate [Member] | Floating rate auction-rate certificates backed by Government guaranteed student loans      
Available-for-sale Securities [Abstract]      
Available-for-Sale Securities Unpaid Principal Balance   46,600agm_AvailableforSaleSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 46,600agm_AvailableforSaleSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Amortized Cost Basis   46,600us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 46,600us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax   0us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 0us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Unrealized Losses   (6,024)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 (6,221)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Fair Value Disclosure   40,576us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 40,379us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Floating Interest Rate [Member] | Asset-backed Securities [Member]      
Available-for-sale Securities [Abstract]      
Available-for-Sale Securities Unpaid Principal Balance   100,730agm_AvailableforSaleSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 100,377agm_AvailableforSaleSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Amortized Cost Basis   100,656us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 100,025us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax   283us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 153us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Unrealized Losses   (37)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 (46)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Fair Value Disclosure   100,902us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 100,132us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Trading Securities [Abstract]      
Trading Securities - Amount Outstanding   2,868agm_TradingSecuritiesAmountOutstanding
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 2,621agm_TradingSecuritiesAmountOutstanding
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Trading Securities, Debt, Amortized Cost   2,868us-gaap_TradingSecuritiesDebtAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 2,621us-gaap_TradingSecuritiesDebtAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Trading Securities, Unrealized Gains 0us-gaap_TradingSecuritiesUnrealizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 0us-gaap_TradingSecuritiesUnrealizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		  
Trading Securities, Unrealized Losses (1,983)us-gaap_TradingSecuritiesUnrealizedHoldingLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 (2,179)us-gaap_TradingSecuritiesUnrealizedHoldingLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		  
Trading, at fair value   689us-gaap_TradingSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 638us-gaap_TradingSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Floating Interest Rate [Member] | Corporate Debt Securities [Member]      
Available-for-sale Securities [Abstract]      
Available-for-Sale Securities Unpaid Principal Balance   10,000agm_AvailableforSaleSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 10,000agm_AvailableforSaleSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Amortized Cost Basis   10,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 10,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax   91us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 85us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Unrealized Losses   0us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 0us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Fair Value Disclosure   10,091us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 10,085us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Floating Interest Rate [Member] | Government/GSE Guaranteed Mortgage Backed Securities [Member]      
Available-for-sale Securities [Abstract]      
Available-for-Sale Securities Unpaid Principal Balance   605,053agm_AvailableforSaleSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 727,430agm_AvailableforSaleSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Amortized Cost Basis   608,484us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 730,868us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax   4,712us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 4,373us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Unrealized Losses   (443)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 (669)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Fair Value Disclosure   612,753us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 734,572us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Floating Interest Rate [Member] | GSE Subordinated Debt [Member}      
Available-for-sale Securities [Abstract]      
Available-for-Sale Securities Unpaid Principal Balance   70,000agm_AvailableforSaleSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 70,000agm_AvailableforSaleSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Amortized Cost Basis   70,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 70,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax   0us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 0us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Unrealized Losses   (3,680)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 (4,159)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Fair Value Disclosure   66,320us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 65,841us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Floating Interest Rate [Member] | Taxable Municipal Bonds [Member]      
Available-for-sale Securities [Abstract]      
Available-for-Sale Securities Unpaid Principal Balance   75,000agm_AvailableforSaleSecuritiesUnpaidPrincipalBalance
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_TaxableMunicipalBondsMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		  
Available-for-sale Securities, Amortized Cost Basis   74,990us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_TaxableMunicipalBondsMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		  
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax   0us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_TaxableMunicipalBondsMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		  
Available-for-sale Securities, Unrealized Losses   (11)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_TaxableMunicipalBondsMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		  
Available-for-sale Securities, Fair Value Disclosure   74,979us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_TaxableMunicipalBondsMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		  
Floating Interest Rate [Member] | Trading Securities [Member] | Asset-backed Securities [Member]      
Available-for-sale Securities [Abstract]      
Unamortized Premium/(Discount)   0us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_TradingAccountAssetsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
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Available-for-sale Securities [Abstract]      
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Available-for-sale Securities [Abstract]      
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Available-for-sale Securities [Abstract]      
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Available-for-sale Securities [Abstract]      
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Available-for-sale Securities [Abstract]      
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Available-for-sale Securities [Abstract]      
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Fixed Interest Rate [Member] | Corporate Debt Securities [Member]      
Available-for-sale Securities [Abstract]      
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Available-for-sale Securities [Abstract]      
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Available-for-sale Securities [Abstract]      
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Available-for-sale Securities [Abstract]      
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Available-for-sale Securities [Abstract]      
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Available-for-sale Securities [Abstract]      
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Available-for-sale Securities [Abstract]      
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Available-for-sale Securities [Abstract]      
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[1] Fair value includes $7.3 million of an interest-only security with a notional amount of $152.4 million.
[2] Fair value includes $7.2 million of an interest-only security with a notional amount of $152.4 million.