Fair Value Disclosures - Unobservable Input Reconciliation (Details) - Level 3 - Recurring - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 6,973,567	$ 7,170,850
Purchases	160,615	483,580
Sales	0	0
Settlements	(244,935)	(227,866)
Allowance for Losses	157	(190)
Realized and unrealized losses included in Income	(168,756)	290,486
Unrealized gains included in Other Comprehensive Income	67,285	(104,545)
Ending Balance	6,787,933	7,612,315
Floating rate auction-rate certificates backed by Government guaranteed student loans \| Floating Interest Rate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	19,171
Ending Balance	19,146
Floating rate auction-rate certificates backed by Government guaranteed student loans \| Floating Interest Rate \| Available-for-Sale Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	19,171	18,912
Purchases	0	0
Sales	0	0
Settlements	0	0
Allowance for Losses	(25)	(24)
Realized and unrealized losses included in Income	0	0
Unrealized gains included in Other Comprehensive Income	0	(2,167)
Ending Balance	19,146	16,721
Available-for-sale securities \| Available-for-Sale Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	19,171	18,912
Purchases	0	0
Sales	0	0
Settlements	0	0
Allowance for Losses	(25)	(24)
Realized and unrealized losses included in Income	0	0
Unrealized gains included in Other Comprehensive Income	0	(2,167)
Ending Balance	19,146	16,721
Farmer Mac Guaranteed Securities \| AgVantage Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	6,947,701
Ending Balance	6,763,209
Farmer Mac Guaranteed Securities \| Available-for-Sale Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	6,947,701	7,143,025
Purchases	160,615	483,580
Sales	0	0
Settlements	(243,832)	(227,255)
Allowance for Losses	182	(166)
Realized and unrealized losses included in Income	(168,742)	290,380
Unrealized gains included in Other Comprehensive Income	67,285	(102,378)
Ending Balance	6,763,209	7,587,186
Farmer Mac Guaranteed Securities \| Available-for-Sale Securities \| AgVantage Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	6,947,701	7,143,025
Purchases	160,615	483,580
Sales	0	0
Settlements	(243,832)	(227,255)
Allowance for Losses	182	(166)
Realized and unrealized losses included in Income	(168,742)	290,380
Unrealized gains included in Other Comprehensive Income	67,285	(102,378)
Ending Balance	6,763,209	7,587,186
USDA Securities:
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	6,695	8,913
Purchases	0	0
Sales	0	0
Settlements	(1,103)	(611)
Allowance for Losses
Realized and unrealized losses included in Income	(14)	106
Unrealized gains included in Other Comprehensive Income	0	0
Ending Balance	5,578	8,408
USDA Securities: \| Trading
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	6,695	8,913
Purchases	0	0
Sales	0	0
Settlements	(1,103)	(611)
Allowance for Losses	0	0
Realized and unrealized losses included in Income	(14)	106
Unrealized gains included in Other Comprehensive Income	0	0
Ending Balance	$ 5,578	$ 8,408

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Allowance for Credit Loss

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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-Publisher FASB
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-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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