Farmer Mac Guaranteed Securities and USDA Guaranteed Securities - Schedule of Held-to-maturity Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Farmer Mac Guaranteed Securities and USDA Securities [Member]
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	$ 4,309,812	$ 4,244,124
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Fair Value [Abstract]
Held-to-maturity Securities, Fair Value	$ 4,242,944	4,179,772
Held-to-Maturity Securities, Debt Maturities, Weighted Average Yield, Single Maturity Date [Abstract]
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Weighted Average Yield	3.16%
Held-to-Maturity Securities, Debt Maturities, After Ten Years, Weighted-Average Yield	3.43%
Farmer Mac Guaranteed Securities [Member]
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	$ 866,596
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	1,352,733
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	209,070
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	2,182,043	2,126,274
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Fair Value [Abstract]
Held-to-maturity Securities, Debt Maturities, Next Twelve Months, Fair Value	865,637
Held-to-maturity Securities, Debt Maturities, Year Two Through Five, Fair Value	1,336,793
Held-to-maturity Securities, Debt Maturities, Year Six Through Ten, Fair Value	204,168
Held-to-maturity Securities, Fair Value	$ 2,166,728	$ 2,116,891
Held-to-Maturity Securities, Debt Maturities, Weighted Average Yield, Single Maturity Date [Abstract]
Held-to-Maturity Securities, Debt Maturities, Next Twelve Months, Weighted-Average Yield	1.79%
Held-to-Maturity Securities, Debt Maturities, Year Two Through Five, Weighted-Average Yield	2.40%
Held-to-Maturity Securities, Debt Maturities, Weighted-Average Yield	2.75%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	$ 1,881,413
Held-to-maturity Securities, Debt Maturities, after Ten Years, Fair Value	$ 1,836,346