Fair Value Disclosures - Unobservable Input Reconciliation (Details) - Level 3 - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 7,612,315	$ 6,470,023	$ 7,170,850	$ 6,003,211
Purchases	351,896	643,183	835,476	1,438,443
Sales	0	(29,419)	0	(48,347)
Settlements	(85,863)	(98,926)	(313,729)	(471,215)
Allowance for losses	(84)		(272)
Realized and unrealized gains/(losses) included in Income	9,030	114,699	299,515	174,095
Unrealized gains/(losses) included in Other Comprehensive Income	37,162	(35,483)	(67,384)	(32,110)
Ending Balance	7,924,456	7,064,077	7,924,456	7,064,077
Available-for-Sale Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	16,721	18,912	18,912	18,715
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Allowance for losses	(15)		(38)
Realized and unrealized gains/(losses) included in Income	0	0	0	0
Unrealized gains/(losses) included in Other Comprehensive Income	1,577	296	(591)	493
Ending Balance	18,283	19,208	18,283	19,208
Available-for-Sale Securities \| Farmer Mac Guaranteed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	7,587,186	6,441,624	7,143,025	5,974,497
Purchases	351,896	613,764	835,476	1,390,096
Sales	0	0	0	0
Settlements	(85,261)	(98,579)	(312,516)	(470,312)
Allowance for losses	(69)		(234)
Realized and unrealized gains/(losses) included in Income	9,050	114,638	299,429	173,990
Unrealized gains/(losses) included in Other Comprehensive Income	35,585	(35,779)	(66,793)	(32,603)
Ending Balance	7,898,387	7,035,668	7,898,387	7,035,668
USDA Securities:
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance			8,913
Ending Balance	7,786		7,786
Institutional Credit \| Available-for-Sale Securities \| Farmer Mac Guaranteed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	7,587,186	6,441,624	7,143,025	5,974,497
Purchases	351,896	613,764	835,476	1,390,096
Sales	0	0	0	0
Settlements	(85,261)	(98,579)	(312,516)	(470,312)
Allowance for losses	(69)		(234)
Realized and unrealized gains/(losses) included in Income	9,050	114,638	299,429	173,990
Unrealized gains/(losses) included in Other Comprehensive Income	35,585	(35,779)	(66,793)	(32,603)
Ending Balance	7,898,387	7,035,668	7,898,387	7,035,668
USDA Guarantees \| Available-for-Sale Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		0		0
Purchases		29,419		48,347
Sales		(29,419)		(48,347)
Settlements		0		0
Realized and unrealized gains/(losses) included in Income		0		0
Unrealized gains/(losses) included in Other Comprehensive Income		0		0
Ending Balance		0		0
USDA Guarantees \| Trading
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	8,408	9,487	8,913	9,999
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(602)	(347)	(1,213)	(903)
Allowance for losses	0		0
Realized and unrealized gains/(losses) included in Income	(20)	61	86	105
Unrealized gains/(losses) included in Other Comprehensive Income	0	0	0	0
Ending Balance	7,786	9,201	7,786	9,201
USDA Guarantees \| USDA Securities:
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	8,408	9,487	8,913	9,999
Purchases	0	29,419	0	48,347
Sales	0	(29,419)	0	(48,347)
Settlements	(602)	(347)	(1,213)	(903)
Allowance for losses
Realized and unrealized gains/(losses) included in Income	(20)	61	86	105
Unrealized gains/(losses) included in Other Comprehensive Income	0	0	0	0
Ending Balance	7,786	9,201	7,786	9,201
Floating Interest Rate \| Available-for-Sale Securities \| Floating rate auction-rate certificates backed by Government guaranteed student loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	16,721	18,912	18,912	18,715
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Allowance for losses	(15)		(38)
Realized and unrealized gains/(losses) included in Income	0	0	0	0
Unrealized gains/(losses) included in Other Comprehensive Income	1,577	296	(591)	493
Ending Balance	$ 18,283	$ 19,208	$ 18,283	$ 19,208

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

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

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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-Section 50
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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.

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-Publisher FASB
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-Section 50
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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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