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Financial Derivatives - Schedule of Derivative Instruments in Statement of Financial Position (Details) - USD ($) | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017
Derivative [Line Items] |  |  |  |  |
Farmer Mac Guaranteed Securities and USDA Securities | $ 76,870,000 | $ 54,350,000 | $ 213,479,000 | $ 146,978,000 |
Notional Disclosures [Abstract] |  |  |  |  |
Derivative, Notional Amount | 9,703,115,000 |  | 9,703,115,000 |  | $ 8,860,296,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |  |  |  |
Financial derivatives, at fair value | 8,007,000 |  | 8,007,000 |  | 7,093,000
Financial derivatives, at fair value | (17,841,000) |  | (17,841,000) |  | (26,599,000)
Derivative, Collateral [Abstract] |  |  |  |  |
Collateral Pledged | 46,841,000 |  | 46,841,000 |  | 24,926,000
Derivative Asset | 8,007,000 |  | 8,007,000 |  | 7,093,000
Loans | 50,622,000 | 40,924,000 | 145,671,000 | 117,349,000 |
Total interest expense | (97,557,000) | (64,935,000) | (265,611,000) | (172,797,000) |
Gain (Loss) on Derivative Instruments, Net, Pretax | (628,000) | (661,000) | 688,000 | (2,530,000) |
TotalAmountsofLineItemsPresentedintheConsolidatedStatementofIncome | 30,563,000 | 31,000,000 | 92,851,000 | 94,060,000 |
Derivative Liability | 29,000,000 |  | 29,000,000 |  | (1,673,000)
Interest Rate Swap [Member] |  |  |  |  |
Notional Disclosures [Abstract] |  |  |  |  |
Derivative, Notional Amount | 9,700,000,000 |  | 9,700,000,000 |  | 8,800,000,000
Fair Value Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Fair Value Hedges Recognized in Earnings | 1,051,000 | 1,742,000 | 5,751,000 | (716,000) |
Income_Expense related to interest settlements on fair value hedges | 6,903,000 | 5,851,000 | 16,331,000 | 16,253,000 |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Derivative | 16,141,000 | 1,576,000 | 45,353,000 | (5,466,000) |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Hedged Item | (15,090,000) | 166,000 | (39,602,000) | 4,750,000 |
Gain (Loss) on Interest Rate Cash Flow Hedge Ineffectiveness |  | (191,000) |  | (365,000) |
Fair Value Hedging [Member] | Interest Rate Swap [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (Loss) on Components Included from Assessment of Interest Rate Fair Value Hedge Effectiveness |  | (1,600,000) |  | 700,000 |
Derivative, Collateral [Abstract] |  |  |  |  |
Derivative Net Interest Settlements | (1,528,000) | (1,892,000) | (5,410,000) | (6,861,000) |
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net |  | 100,000 |  | 0 |
Cash Flow Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax | 189,000 | (454,000) | (21,000) | (1,494,000) |
Premium_Discount recognized on hedged item | (2,000) | (1,000) | (5,000) | (3,000) |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Hedged Item | (2,501,000) | (1,169,000) | (6,611,000) | (2,665,000) |
Unrealized Gain (Loss) on Cash Flow Hedging Instruments | (2,314,000) | (1,815,000) | (6,637,000) | (4,527,000) |
Cash [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Obligation to Return Securities Received as Collateral | 0 |  | 0 |  | 0
Collateral Pledged | 0 |  | 0 |  | 100,000
Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Hedged Item Net Interest Settlements | 8,608,000 | 7,864,000 | 22,275,000 | 23,425,000 |
Premium_Discount recognized on hedged item | (177,000) | (121,000) | (534,000) | (311,000) |
Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] | Interest Rate Swap, Pay Fixed Non-Callable [Member] |  |  |  |  |
Notional Disclosures [Abstract] |  |  |  |  |
Derivative, Notional Amount | 2,801,164,000 |  | 2,801,164,000 |  | 2,086,347,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |  |  |  |
Financial derivatives, at fair value | 860,000 |  | 860,000 |  | 5,240,000
Financial derivatives, at fair value | $ (4,493,000) |  | $ (4,493,000) |  | $ (5,990,000)
Derivative, Average Fixed Interest Rate | 2.04% |  | 2.04% |  | 1.88%
Derivative, Average Variable Interest Rate | 2.13% |  | 2.13% |  | 1.40%
Derivative, Average Remaining Maturity |  |  | 10 years 4 months 22 days |  | 5 years 5 months 17 days
Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] | Interest Rate Swap, Receive Fixed Non-Callable [Member] |  |  |  |  |
Notional Disclosures [Abstract] |  |  |  |  |
Derivative, Notional Amount | $ 2,131,200,000 |  | $ 2,131,200,000 |  | $ 1,559,700,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |  |  |  |
Financial derivatives, at fair value | 682,000 |  | 682,000 |  | 110,000
Financial derivatives, at fair value | $ (4,796,000) |  | $ (4,796,000) |  | $ (4,033,000)
Derivative, Average Fixed Interest Rate | 2.20% |  | 2.20% |  | 1.38%
Derivative, Average Variable Interest Rate | 1.78% |  | 1.78% |  | 1.45%
Derivative, Average Remaining Maturity |  |  | 1 year 8 months 28 days |  | 1 year 8 months 5 days
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest Rate Swap, Pay Fixed Non-Callable [Member] |  |  |  |  |
Notional Disclosures [Abstract] |  |  |  |  |
Derivative, Notional Amount | $ 389,500,000 |  | $ 389,500,000 |  | $ 365,500,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |  |  |  |
Financial derivatives, at fair value | 4,429,000 |  | 4,429,000 |  | 1,402,000
Financial derivatives, at fair value | $ (276,000) |  | $ (276,000) |  | $ (138,000)
Derivative, Average Fixed Interest Rate | 2.36% |  | 2.36% |  | 2.16%
Derivative, Average Variable Interest Rate | 2.57% |  | 2.57% |  | 1.74%
Derivative, Average Remaining Maturity |  |  | 6 years 1 month 6 days |  | 5 years 10 months 3 days
Not Designated as Hedging Instrument [Member] |  |  |  |  |
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |  |  |  |
Derivative Credit Risk Valuation Adjustment, Derivative Assets | $ 163,000 |  | $ 163,000 |  | $ 16,000
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities | 6,000 |  | 6,000 |  | 56,000
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax |  | 890,000 |  | (3,611,000) |
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Total interest expense | (3,048,000) | (2,676,000) | (8,903,000) | (8,318,000) |
Gain (Loss) on Derivative Instruments, Net, Pretax | (3,267,000) | (1,645,000) | (7,443,000) | (12,324,000) |
Not Designated as Hedging Instrument [Member] | Interest Rate Swap, Pay Fixed Non-Callable [Member] |  |  |  |  |
Notional Disclosures [Abstract] |  |  |  |  |
Derivative, Notional Amount | 317,586,000 |  | 317,586,000 |  | 345,333,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |  |  |  |
Financial derivatives, at fair value | 1,966,000 |  | 1,966,000 |  | 339,000
Financial derivatives, at fair value | $ (8,065,000) |  | $ (8,065,000) |  | $ (16,352,000)
Derivative, Average Fixed Interest Rate | 3.69% |  | 3.69% |  | 3.79%
Derivative, Average Variable Interest Rate | 2.33% |  | 2.33% |  | 1.40%
Derivative, Average Remaining Maturity |  |  | 6 years 5 months 22 days |  | 6 years 8 months 5 days
Not Designated as Hedging Instrument [Member] | Interest Rate Swap, Receive Fixed Non-Callable [Member] |  |  |  |  |
Notional Disclosures [Abstract] |  |  |  |  |
Derivative, Notional Amount | $ 2,521,965,000 |  | $ 2,521,965,000 |  | $ 3,409,916,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |  |  |  |
Financial derivatives, at fair value | 0 |  | 0 |  | 0
Financial derivatives, at fair value | $ 0 |  | $ 0 |  | $ 0
Derivative, Average Fixed Interest Rate | 1.99% |  | 1.99% |  | 1.24%
Derivative, Average Variable Interest Rate | 2.16% |  | 2.16% |  | 1.25%
Derivative, Average Remaining Maturity |  |  | 9 months 32 days |  | 11 months
Not Designated as Hedging Instrument [Member] | Basis Swap [Member] |  |  |  |  |
Notional Disclosures [Abstract] |  |  |  |  |
Derivative, Notional Amount | $ 1,529,000,000 |  | $ 1,529,000,000 |  | $ 1,053,500,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |  |  |  |
Financial derivatives, at fair value | 233,000 |  | 233,000 |  | 18,000
Financial derivatives, at fair value | $ (206,000) |  | $ (206,000) |  | $ (106,000)
Derivative, Average Variable Interest Rate | 2.01% |  | 2.01% |  | 1.33%
Derivative, Variable Interest Rate | 2.07% |  | 2.07% |  | 1.42%
Derivative, Average Remaining Maturity |  |  | 1 year 4 months 28 days |  | 10 months 28 days
Not Designated as Hedging Instrument [Member] | Forward Contracts [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax |  | 0 |  | 588,000 |
Not Designated as Hedging Instrument [Member] | Future [Member] |  |  |  |  |
Notional Disclosures [Abstract] |  |  |  |  |
Derivative, Notional Amount | $ 12,700,000 |  | $ 12,700,000 |  | $ 40,000,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract] |  |  |  |  |
Financial derivatives, at fair value | 0 |  | 0 |  | 0
Financial derivatives, at fair value | (11,000) |  | $ (11,000) |  | $ (36,000)
Derivative, Weighted-Average Forward Price |  |  | $ 118.70 |  | $ 123.96
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax | (409,000) | (141,000) | $ (772,000) | (193,000) |
Interest Income [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax | 0 |  | 0 |  |
Interest Income [Member] | Fair Value Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Fair Value Hedges Recognized in Earnings | (12,000) | 0 | 3,125,000 | 0 |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Hedged Item | (13,432,000) | 0 | (43,229,000) | 0 |
Interest Income [Member] | Fair Value Hedging [Member] | Interest Rate Swap [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Derivative Net Interest Settlements | 1,272,000 | (2,267,000) | 465,000 | (8,251,000) |
Income_Expense related to interest settlements on fair value hedges | 18,041,000 | 9,719,000 | 46,754,000 | 25,961,000 |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Derivative | 13,420,000 | 0 | 46,354,000 | 0 |
Gain (Loss) on Interest Rate Cash Flow Hedge Ineffectiveness |  | 0 |  | 0 |
Interest Income [Member] | Cash Flow Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax | 0 | 0 | 0 | 0 |
Premium_Discount recognized on hedged item | 0 | 0 | 0 | 0 |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Hedged Item | 0 | 0 | 0 | 0 |
Unrealized Gain (Loss) on Cash Flow Hedging Instruments | 0 | 0 | 0 | 0 |
Interest Income [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Hedged Item Net Interest Settlements | 16,769,000 | 11,986,000 | 46,289,000 | 34,212,000 |
Premium_Discount recognized on hedged item | 0 | 0 | 0 | 0 |
Interest Income [Member] | Not Designated as Hedging Instrument [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax |  | 0 |  | 0 |
Interest Income [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Total interest expense | 0 | 0 | 0 | 0 |
Gain (Loss) on Derivative Instruments, Net, Pretax | 0 | 0 | 0 | 0 |
Interest Income [Member] | Not Designated as Hedging Instrument [Member] | Forward Contracts [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax |  | 0 |  | 0 |
Interest Income [Member] | Not Designated as Hedging Instrument [Member] | Future [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax | 0 | 0 | 0 | 0 |
Loans and Finance Receivables [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax | 0 |  | 0 |  |
Loans and Finance Receivables [Member] | Fair Value Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Fair Value Hedges Recognized in Earnings | (153,000) | 0 | (542,000) | 0 |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Hedged Item | (4,062,000) | 0 | (13,106,000) | 0 |
Loans and Finance Receivables [Member] | Fair Value Hedging [Member] | Interest Rate Swap [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Derivative Net Interest Settlements | (98,000) | (342,000) | (560,000) | (767,000) |
Income_Expense related to interest settlements on fair value hedges | 1,562,000 | 605,000 | 4,059,000 | 1,278,000 |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Derivative | 3,909,000 | 0 | 12,564,000 | 0 |
Gain (Loss) on Interest Rate Cash Flow Hedge Ineffectiveness |  | 0 |  | 0 |
Loans and Finance Receivables [Member] | Cash Flow Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax | 0 | 0 | 0 | 0 |
Premium_Discount recognized on hedged item | 0 | 0 | 0 | 0 |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Hedged Item | 0 | 0 | 0 | 0 |
Unrealized Gain (Loss) on Cash Flow Hedging Instruments | 0 | 0 | 0 | 0 |
Loans and Finance Receivables [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Hedged Item Net Interest Settlements | 1,660,000 | 947,000 | 4,619,000 | 2,045,000 |
Premium_Discount recognized on hedged item | 0 | 0 | 0 | 0 |
Loans and Finance Receivables [Member] | Not Designated as Hedging Instrument [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax |  | 0 |  | 0 |
Loans and Finance Receivables [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Total interest expense | 0 | 0 | 0 | 0 |
Gain (Loss) on Derivative Instruments, Net, Pretax | 0 | 0 | 0 | 0 |
Loans and Finance Receivables [Member] | Not Designated as Hedging Instrument [Member] | Forward Contracts [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax |  | 0 |  | 0 |
Loans and Finance Receivables [Member] | Not Designated as Hedging Instrument [Member] | Future [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax | 0 | 0 | 0 | 0 |
Interest Expense [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax | 0 |  |  |  |
Interest Expense [Member] | Fair Value Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Fair Value Hedges Recognized in Earnings | 1,216,000 | 0 | 3,168,000 | 0 |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Hedged Item | 2,404,000 | 0 | 16,733,000 | 0 |
Interest Expense [Member] | Fair Value Hedging [Member] | Interest Rate Swap [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Derivative Net Interest Settlements | (2,702,000) | 717,000 | (5,315,000) | 2,157,000 |
Income_Expense related to interest settlements on fair value hedges | (12,700,000) | (4,473,000) | (34,482,000) | (10,986,000) |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Derivative | (1,188,000) | 0 | (13,565,000) | 0 |
Gain (Loss) on Interest Rate Cash Flow Hedge Ineffectiveness |  | 0 |  | 0 |
Interest Expense [Member] | Cash Flow Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax | 189,000 | (454,000) | (21,000) | (1,494,000) |
Premium_Discount recognized on hedged item | (2,000) | (1,000) | (5,000) | (3,000) |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Hedged Item | (2,501,000) | (1,169,000) | (6,611,000) | (2,665,000) |
Unrealized Gain (Loss) on Cash Flow Hedging Instruments | (2,314,000) | (1,624,000) | (6,637,000) | (4,162,000) |
Interest Expense [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Hedged Item Net Interest Settlements | (9,821,000) | (5,069,000) | (28,633,000) | (12,832,000) |
Premium_Discount recognized on hedged item | (177,000) | (121,000) | (534,000) | (311,000) |
Interest Expense [Member] | Not Designated as Hedging Instrument [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax |  | 0 | 0 | 0 |
Interest Expense [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Total interest expense | 0 | 0 | 0 | 0 |
Gain (Loss) on Derivative Instruments, Net, Pretax | 0 | 0 | 0 | 0 |
Interest Expense [Member] | Not Designated as Hedging Instrument [Member] | Forward Contracts [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax |  | 0 |  | 0 |
Interest Expense [Member] | Not Designated as Hedging Instrument [Member] | Future [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax | 0 | 0 | 0 | 0 |
Gain (Loss) on Derivative Instruments [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax | (628,000) | 890,000 | 688,000 | (3,611,000) |
Gain (Loss) on Derivative Instruments [Member] | Fair Value Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Derivative Net Interest Settlements | 0 | 0 | 0 | 0 |
Gain (Loss) on Fair Value Hedges Recognized in Earnings | 0 | 1,742,000 | 0 | (716,000) |
Income_Expense related to interest settlements on fair value hedges | 0 | 0 | 0 | 0 |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Derivative | 0 | 1,576,000 | 0 | (5,466,000) |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Hedged Item | 0 | 166,000 | 0 | 4,750,000 |
Gain (Loss) on Interest Rate Cash Flow Hedge Ineffectiveness |  | (191,000) |  | (365,000) |
Gain (Loss) on Derivative Instruments [Member] | Cash Flow Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax | 0 | 0 | 0 | 0 |
Premium_Discount recognized on hedged item | 0 | 0 | 0 | 0 |
Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Hedged Item | 0 | 0 | 0 | 0 |
Unrealized Gain (Loss) on Cash Flow Hedging Instruments | 0 | (191,000) | 0 | (365,000) |
Gain (Loss) on Derivative Instruments [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Hedged Item Net Interest Settlements | 0 | 0 | 0 | 0 |
Premium_Discount recognized on hedged item | 0 | 0 | 0 | 0 |
Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Total interest expense | (3,048,000) | (2,676,000) | (8,903,000) | (8,318,000) |
Gain (Loss) on Derivative Instruments, Net, Pretax | (3,267,000) | (1,645,000) | (7,443,000) | (12,324,000) |
Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument [Member] | Forward Contracts [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax |  | 0 |  | 588,000 |
Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument [Member] | Future [Member] |  |  |  |  |
Derivative, Collateral [Abstract] |  |  |  |  |
Gain (Loss) on Derivative Instruments, Net, Pretax | $ (409,000) | $ (141,000) | $ (772,000) | $ (193,000) |

X
- Definition Derivative, Net Hedge Ineffectiveness Gain (Loss), Component recognized on Derivative. + References No definition available. + Details
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Namespace Prefix: | agm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Derivative Net Hedge Ineffectiveness Gain Loss Component Recognized On Hedged Item + References No definition available. + Details
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Namespace Prefix: | agm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition Derivative Net Interest Settlements (Interest Accruals) + References No definition available. + Details
Name: | agm_DerivativeNetInterestSettlements
Namespace Prefix: | agm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Derivative, Weighted-Average Forward Price + References No definition available. + Details
Name: | agm_DerivativeWeightedAverageForwardPrice
Namespace Prefix: | agm_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

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- Definition Gain (Loss) on Components Other Than Fair Value Changes Included in Assessment of Interest Rate Fair Value Hedge Effectiveness + References No definition available. + Details
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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition Variable interest rate in effect as of the balance sheet date related to the interest rate derivative. + References No definition available. + Details
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- Definition Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959 + Details
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- Definition Amount of gain (loss)recognized in the income statement from the hedging ineffectiveness of a fair value hedge. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986 + Details
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- Definition Total amount of gain (loss) derived from fair value hedges recognized in earnings in the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 + Details
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- Definition The net gain (loss) during the reporting period due to ineffectiveness in interest rate cash flow hedges. Recognized in earnings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 + Details
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- Definition The aggregate interest and fee income generated by: (1) loans the Entity has positive intent and ability to hold for the foreseeable future, or until maturity or payoff, including commercial and consumer loans, whether domestic or foreign, which may consist of: (a) industrial and agricultural; (b) real estate; and (c) real estate construction loans; (d) trade financing; (e) lease financing; (f) home equity lines-of-credit; (g) automobile and other vehicle loans; and (h) credit card and other revolving-type loans and (2) loans and leases held-for-sale which may include mortgage loans, direct financing, and sales-type leases. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.1) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 + Details
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