Fair Value Disclosures - Unobservable Input Reconciliation (Details) - Fair Value, Inputs, Level 3 [Member] - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 7,064,077	$ 6,015,564	$ 6,003,211	$ 5,508,576
Cumulative Effect from Change in Hedge Accounting				487
Purchases	349,654	713,702	1,788,097	1,751,973
Sales	(9,506)	(26,321)	(57,853)	(105,628)
Settlements	(254,900)	(689,721)	(726,116)	(1,134,113)
Realized and Unrealized Gains included in Income	84,213	(13,435)	258,309	(45,298)
Unrealized Losses included in Other Comprehensive Income	(22,846)	(13,287)	(54,956)	10,505
Ending Balance	7,210,692	5,986,502	7,210,692	5,986,502
USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	9,201	10,748	9,999	13,515
Cumulative Effect from Change in Hedge Accounting				0
Purchases	9,506	26,321	57,853	105,628
Sales	(9,506)	(26,321)	(57,853)	(105,628)
Settlements	(307)	(508)	(1,210)	(3,302)
Realized and Unrealized Gains included in Income	49	(3)	154	24
Unrealized Losses included in Other Comprehensive Income	0	0	0	0
Ending Balance	8,943	10,237	8,943	10,237
Debt Securities, Trading, Unrealized Loss		9		100
Available-for-sale Securities [Member] \| Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	19,208	19,010	18,715	23,147
Cumulative Effect from Change in Hedge Accounting				0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	(2,137)
Realized and Unrealized Gains included in Income	0	0	0	(2,092)
Unrealized Losses included in Other Comprehensive Income	0	(49)	493	43
Ending Balance	19,208	18,961	19,208	18,961
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	7,035,668	5,985,806	5,974,497	5,471,914
Cumulative Effect from Change in Hedge Accounting				487
Purchases	340,148	687,381	1,730,244	1,646,345
Sales	0	0	0	0
Settlements	(254,593)	(689,213)	(724,906)	(1,128,674)
Realized and Unrealized Gains included in Income	84,164	(13,432)	258,155	(43,230)
Unrealized Losses included in Other Comprehensive Income	(22,846)	(13,238)	(55,449)	10,462
Ending Balance	7,182,541	5,957,304	7,182,541	5,957,304
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	9,506	26,321	57,853	105,628
Sales	(9,506)	(26,321)	(57,853)	(105,628)
Settlements	0	0	0	0
Realized and Unrealized Gains included in Income	0	0	0	0
Unrealized 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	9,201	10,748	9,999	13,515
Cumulative Effect from Change in Hedge Accounting				0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(307)	(508)	(1,210)	(3,302)
Realized and Unrealized Gains included in Income	49	(3)	154	24
Unrealized Losses included in Other Comprehensive Income	0	0	0	0
Ending Balance	8,943	10,237	8,943	10,237
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	7,035,668	5,985,806	5,974,497	5,471,914
Cumulative Effect from Change in Hedge Accounting				487
Purchases	340,148	687,381	1,730,244	1,646,345
Sales	0	0	0	0
Settlements	(254,593)	(689,213)	(724,906)	(1,128,674)
Realized and Unrealized Gains included in Income	84,164	(13,432)	258,155	(43,230)
Unrealized Losses included in Other Comprehensive Income	(22,846)	(13,238)	(55,449)	10,462
Ending Balance	7,182,541	5,957,304	7,182,541	5,957,304
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	19,208	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 Losses included in Other Comprehensive Income	0	(49)	493	147
Ending Balance	$ 19,208	18,961	$ 19,208	18,961
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				4,333
Cumulative Effect from Change in Hedge Accounting				0
Purchases				0
Sales				0
Settlements				(2,137)
Realized and Unrealized Gains included in Income				(2,092)
Unrealized Losses included in Other Comprehensive Income				(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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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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