Fair Value Disclosures - Unobservable Input Reconciliation (Details) - Fair Value, Inputs, Level 3 [Member] - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 6,470,023	$ 5,874,075	$ 6,003,211	$ 5,508,576
Cumulative Effect from Change in Hedge Accounting				487
Purchases	643,183	348,531	1,438,443	1,038,271
Sales	(29,419)	(45,014)	(48,347)	(79,307)
Settlements	(98,926)	(152,042)	(471,215)	(444,392)
Realized and Unrealized Gains included in Income	114,699	(12,931)	174,095	(31,863)
Unrealized Gains/(Losses) included in Other Comprehensive Income	(35,483)	2,945	(32,110)	23,792
Ending Balance	7,064,077	6,015,564	7,064,077	6,015,564
USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	9,487	11,558	9,999	13,515
Cumulative Effect from Change in Hedge Accounting				0
Purchases	29,419	45,014	48,347	79,307
Sales	(29,419)	(45,014)	(48,347)	(79,307)
Settlements	(347)	(821)	(903)	(2,794)
Realized and Unrealized Gains included in Income	61	11	105	27
Unrealized Gains/(Losses) included in Other Comprehensive Income	0	0	0	0
Ending Balance	9,201	10,748	9,201	10,748
Unrealized Gains				100
Available-for-sale Securities [Member] \| Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	18,912	23,130	18,715	23,147
Cumulative Effect from Change in Hedge Accounting				0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	0	(2,028)	0	(2,137)
Realized and Unrealized Gains included in Income	0	(2,092)	0	(2,092)
Unrealized Gains/(Losses) included in Other Comprehensive Income	296	0	493	92
Ending Balance	19,208	19,010	19,208	19,010
Available-for-sale Securities [Member] \| Farmer Mac Guaranteed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	6,441,624	5,839,387	5,974,497	5,471,914
Cumulative Effect from Change in Hedge Accounting				487
Purchases	613,764	303,517	1,390,096	958,964
Sales	0	0	0	0
Settlements	(98,579)	(149,193)	(470,312)	(439,461)
Realized and Unrealized Gains included in Income	114,638	(10,850)	173,990	(29,798)
Unrealized Gains/(Losses) included in Other Comprehensive Income	(35,779)	2,945	(32,603)	23,700
Ending Balance	7,035,668	5,985,806	7,035,668	5,985,806
Available-for-sale Securities [Member] \| USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	0	0	0	0
Cumulative Effect from Change in Hedge Accounting				0
Purchases	29,419	45,014	48,347	79,307
Sales	(29,419)	(45,014)	(48,347)	(79,307)
Settlements	0	0	0	0
Realized and Unrealized Gains included in Income	0	0	0	0
Unrealized Gains/(Losses) included in Other Comprehensive Income	0	0	0	0
Ending Balance	0	0	0	0
Trading Securities [Member] \| USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	9,487	11,558	9,999	13,515
Cumulative Effect from Change in Hedge Accounting				0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(347)	(821)	(903)	(2,794)
Realized and Unrealized Gains included in Income	61	11	105	27
Unrealized Gains/(Losses) included in Other Comprehensive Income	0	0	0	0
Ending Balance	9,201	10,748	9,201	10,748
Institutional Credit [Member] \| Available-for-sale Securities [Member] \| Farmer Mac Guaranteed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	6,441,624	5,839,387	5,974,497	5,471,914
Cumulative Effect from Change in Hedge Accounting				487
Purchases	613,764	303,517	1,390,096	958,964
Sales	0	0	0	0
Settlements	(98,579)	(149,193)	(470,312)	(439,461)
Realized and Unrealized Gains included in Income	114,638	(10,850)	173,990	(29,798)
Unrealized Gains/(Losses) included in Other Comprehensive Income	(35,779)	2,945	(32,603)	23,700
Ending Balance	7,035,668	5,985,806	7,035,668	5,985,806
Floating Interest Rate [Member] \| Available-for-sale Securities [Member] \| 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	19,010	18,715	18,814
Cumulative Effect from Change in Hedge Accounting				0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Realized and Unrealized Gains included in Income	0	0	0	0
Unrealized Gains/(Losses) included in Other Comprehensive Income	296	0	493	196
Ending Balance	$ 19,208	19,010	$ 19,208	19,010
Fixed Interest Rate [Member] \| Available-for-sale Securities [Member] \| Collateralized Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		4,120		4,333
Cumulative Effect from Change in Hedge Accounting				0
Purchases		0		0
Sales		0		0
Settlements		(2,028)		(2,137)
Realized and Unrealized Gains included in Income		(2,092)		(2,092)
Unrealized Gains/(Losses) included in Other Comprehensive Income		0		(104)
Ending Balance		$ 0		$ 0

Amount of unrealized gain on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

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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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Amount of gain (loss) recognized in the income statement for 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 gain (loss) recognized in other comprehensive income (loss) for 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 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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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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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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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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