Farmer Mac Guaranteed Securities and USDA Guaranteed Securities - Schedule of Available-for-sale Securities (Details) - Farmer Mac Guaranteed Securities and USDA Securities [Member] $ in Thousands	Dec. 31, 2018 USD ($)
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Available-for-sale Securities, Due within one year, Amortized Cost	$ 618,461
Available-for-sale Securities, Due after one year through five years, Amortized Cost	2,889,110
Available-for-sale Securities, Due after five years through ten years, Amortized Cost	1,248,615
Available-for-sale Securities, Due after ten years, Amortized Cost	1,247,343
Available-for-sale Securities, Amortized Cost Basis	6,003,529
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract]
Available-for-sale Securities, Due within one year, Fair Value	618,825
Available-for-sale Securities, Due after one year through five years, Fair Value	2,887,325
Available-for-sale Securities, Due after five years through ten years, Fair Value	1,239,658
Available-for-sale Securities, Due after ten years, Fair Value	1,228,689
Available-for-sale, at fair value	$ 5,974,497
Available-for-sale Securities, Debt Maturities, Weighted Average Yield, Single Maturity Date [Abstract]
Available-for-sale Securities, Due within one year, Weighted-Average Yield	2.87%
Available-for-sale Securities, Due after one year through five years, Weighted-Average Yield	3.12%
Available-for-sale Securities, Due after five years through ten years, Weighted-Average Yield	3.21%
Available-for-sale Securities, Due after ten years, Weighted-Average Yield	3.61%
Available-for-sale Securities, Total Weighted-Average Yield	3.22%

Available-for-sale Securities, Debt Maturities, after Ten Years, Weighted-Average Yield

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Available-for-sale Securities, Debt Maturities, Next Twelve Months, Weighted-Average Yield

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Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Weighted-Average Yield

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Available-for-sale Securities, Debt Maturities, Year Two Through Five, Weighted-Average Yield

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Available-for-sale Securities, Debt Maturities, Weighted Average Yield, Single Maturity Date [Abstract]

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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