Fair Value Disclosures - Unobservable Input Reconciliation (Details) - Level 3 - Recurring - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 6,901,703	$ 7,924,456	$ 6,973,567	$ 7,170,850
Purchases	0	122,892	578,115	958,368
Sales	0	0	0	0
Settlements	(709,176)	(514,561)	(1,264,981)	(828,290)
Allowance for Losses	(64)	(95)	3	(367)
Realized and unrealized gains/(losses) included in Income	(31,425)	(42,091)	(150,303)	257,424
Unrealized gains/(losses) included in Other Comprehensive Income	2,014	46,939	26,651	(20,445)
Ending Balance	6,163,052	7,537,540	6,163,052	7,537,540
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	19,500		19,500
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	19,248	18,283	19,171	18,912
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Allowance for Losses	6	1	(16)	(37)
Realized and unrealized gains/(losses) included in Income	0	0	0	0
Unrealized gains/(losses) included in Other Comprehensive Income	246	788	345	197
Ending Balance	19,500	19,072	19,500	19,072
Available-for-sale securities \| Available-for-Sale Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	19,248	18,283	19,171	18,912
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Allowance for Losses	6	1	(16)	(37)
Realized and unrealized gains/(losses) included in Income	0	0	0	0
Unrealized gains/(losses) included in Other Comprehensive Income	246	788	345	197
Ending Balance	19,500	19,072	19,500	19,072
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	6,138,759		6,138,759
Farmer Mac Guaranteed Securities \| Available-for-Sale Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	6,877,405	7,898,387	6,947,701	7,143,025
Purchases	0	122,892	578,115	958,368
Sales	0	0	0	0
Settlements	(708,882)	(513,864)	(1,263,117)	(826,380)
Allowance for Losses	(70)	(96)	19	(330)
Realized and unrealized gains/(losses) included in Income	(31,462)	(41,832)	(150,265)	257,597
Unrealized gains/(losses) included in Other Comprehensive Income	1,768	46,151	26,306	(20,642)
Ending Balance	6,138,759	7,511,638	6,138,759	7,511,638
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	6,877,405	7,898,387	6,947,701	7,143,025
Purchases	0	122,892	578,115	958,368
Sales	0	0	0	0
Settlements	(708,882)	(513,864)	(1,263,117)	(826,380)
Allowance for Losses	(70)	(96)	19	(330)
Realized and unrealized gains/(losses) included in Income	(31,462)	(41,832)	(150,265)	257,597
Unrealized gains/(losses) included in Other Comprehensive Income	1,768	46,151	26,306	(20,642)
Ending Balance	6,138,759	7,511,638	6,138,759	7,511,638
USDA Securities:
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	5,050	7,786	6,695	8,913
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(294)	(697)	(1,864)	(1,910)
Allowance for Losses
Realized and unrealized gains/(losses) included in Income	37	(259)	(38)	(173)
Unrealized gains/(losses) included in Other Comprehensive Income	0	0	0	0
Ending Balance	4,793	6,830	4,793	6,830
USDA Securities: \| Trading
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	5,050	7,786	6,695	8,913
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(294)	(697)	(1,864)	(1,910)
Allowance for Losses	0	0	0	0
Realized and unrealized gains/(losses) included in Income	37	(259)	(38)	(173)
Unrealized gains/(losses) included in Other Comprehensive Income	0	0	0	0
Ending Balance	$ 4,793	$ 6,830	$ 4,793	$ 6,830

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=123874694&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=123874694&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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