Fair Value Disclosures - Unobservable Input Reconciliation (Details) - Level 3 - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 7,170,850	$ 6,003,211
Purchases	483,580	795,260
Sales	0	(18,928)
Settlements	(227,866)	(372,289)
Allowance for losses	(190)
Realized and Unrealized Gains included in Income	290,486	59,396
Unrealized Gains included in Other Comprehensive Income	(104,545)	3,373
Ending Balance	7,612,315	6,470,023
Available-for-Sale Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	18,912	18,715
Purchases	0	0
Sales	0	0
Settlements	0	0
Allowance for losses	(24)
Realized and Unrealized Gains included in Income	0	0
Unrealized Gains included in Other Comprehensive Income	(2,167)	197
Ending Balance	16,721	18,912
Available-for-Sale Securities \| Farmer Mac Guaranteed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	7,143,025	5,974,497
Purchases	483,580	776,332
Sales	0	0
Settlements	(227,255)	(371,733)
Allowance for losses	(166)
Realized and Unrealized Gains included in Income	290,380	59,352
Unrealized Gains included in Other Comprehensive Income	(102,378)	3,176
Ending Balance	7,587,186	6,441,624
USDA Securities:
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	8,913
Ending Balance	8,408
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	7,143,025	5,974,497
Purchases	483,580	776,332
Sales	0	0
Settlements	(227,255)	(371,733)
Allowance for losses	(166)
Realized and Unrealized Gains included in Income	290,380	59,352
Unrealized Gains included in Other Comprehensive Income	(102,378)	3,176
Ending Balance	7,587,186	6,441,624
USDA Guarantees \| Available-for-Sale Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		0
Purchases		18,928
Sales		(18,928)
Settlements		0
Realized and Unrealized Gains included in Income		0
Unrealized Gains included in Other Comprehensive Income		0
Ending Balance		0
USDA Guarantees \| Trading
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	8,913	9,999
Purchases	0	0
Sales	0	0
Settlements	(611)	(556)
Allowance for losses	0
Realized and Unrealized Gains included in Income	106	44
Unrealized Gains included in Other Comprehensive Income	0	0
Ending Balance	8,408	9,487
USDA Guarantees \| USDA Securities:
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	8,913	9,999
Purchases	0	18,928
Sales	0	(18,928)
Settlements	(611)	(556)
Allowance for losses
Realized and Unrealized Gains included in Income	106	44
Unrealized Gains included in Other Comprehensive Income	0	0
Ending Balance	8,408	9,487
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	18,912	18,715
Purchases	0	0
Sales	0	0
Settlements	0	0
Allowance for losses	(24)
Realized and Unrealized Gains included in Income	0	0
Unrealized Gains included in Other Comprehensive Income	(2,167)	197
Ending Balance	$ 16,721	$ 18,912

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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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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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

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-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
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-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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