Related Party Transactions - National Rural Utilities Cooperative Financial Corporation (Details) - CFC [Member] - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	$ 986,645	$ 487,341	$ 741,895
Related Party Transaction, Related Party's percent of total Program	19.10%	10.30%	16.70%
Related Party's percent of Farmer Mac Total Outstanding Book of Business	23.60%	24.60%
Related Party Transaction, Other Revenues from Transactions with Related Party	$ 57	$ 65	$ 74
Due from Related Parties	9,400	5,200
Interest Income, Related Party	76,800	43,900	27,600
Accounts Receivable, Related Parties, Current	100
Revenue from Related Parties	1,900	2,200	2,000
Related Party Transaction, Expenses from Transactions with Related Party	$ 3,600	$ 3,500	$ 3,300
Rural Utilities [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Related Party's percent of total Program	100.00%
Institutional Credit [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Related Party's percent of total Program	29.50%	14.70%	11.90%
Real Estate Loan [Member] \| Rural Utilities [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	$ 11,645	$ 137,341	$ 50,491
Guarantee Obligations [Member] \| Rural Utilities [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	675,000	350,000	250,000
Farmer Mac Guaranteed Securities [Member] \| Off-balance sheet [Member] \| Institutional Credit [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	300,000	0	0
Revolving Credit Facility [Member] \| Off-balance sheet [Member] \| Institutional Credit [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	$ 0	$ 0	$ 441,404
Common Class A [Member]
Related Party Transaction [Line Items]
Common Stock Ownership Percentage by a Related Party	7.90%

Common Stock Ownership Percentage by a Related Party

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Related Party Transaction, Related Party's percent of total Program

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Related Party's percent of Farmer Mac Total Outstanding Book of Business

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Amount of receivables arising from transactions with related parties due within one year or the normal operating cycle, if longer.

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For an unclassified balance sheet, amounts due from related parties including affiliates, employees, joint ventures, officers and stockholders, immediate families thereof, and pension funds.

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Amount of interest income earned from interest-bearing assets owed to the entity by related party.

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Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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Purchases during the period (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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