Guarantees and Long Term Standby Purchase Commitments - Cash Flows from Off-balance sheet Guaranteed Securities (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Guarantor Obligations [Line Items]
Proceeds from sale of Farmer Mac Guaranteed Securities	$ 305,391	$ 404,246
Proceeds from Fees Received	1,481	2,141
Payments to Acquire Loans and Leases Held-for-investment	$ (6,273)	$ (3,147)
Farmer Mac Guaranteed Securities [Member]
Guarantor Obligations [Line Items]
Weighted average remaining maturity, Loans underlying guarantees not held by transferor	9 years 5 months 15 days		10 years
Farmer Mac Guaranteed Securities [Member] \| Variable Interest Entity, Not Primary Beneficiary [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	$ 3,100		$ 3,600
Institutional Credit [Member] \| Farmer Mac Guaranteed Securities [Member]
Guarantor Obligations [Line Items]
Weighted average remaining maturity, Loans underlying guarantees not held by transferor	5 years 3 months 15 days		9 months 15 days

Weighted average remaining maturity, Loans underlying guarantees not held by transferor

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- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The cash outflow from (a) purchases of loans held-for-investment, (b) purchases of leases held-for-investment, and (c) both.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585

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- Definition

Cash received for fees during the current period. This element excludes cash proceeds from license fees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585

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Amount of cash inflow from the sale of investments classified as other.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3521-108585

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 26
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3574-108585

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