Farmer Mac Guaranteed Securities and USDA Guaranteed Securities - Schedule of Held-to-maturity Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
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	$ 4,251,095	$ 3,158,456
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Fair Value [Abstract]
Held-to-maturity Securities, Fair Value	$ 4,185,174	3,066,644
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	3.07%
Held-to-Maturity Securities, Debt Maturities, After Ten Years, Weighted-Average Yield	3.35%
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	$ 926,747
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	1,260,842
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	208,034
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	2,158,810	1,149,231
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Fair Value [Abstract]
Held-to-maturity Securities, Debt Maturities, Next Twelve Months, Fair Value	925,935
Held-to-maturity Securities, Debt Maturities, Year Two Through Five, Fair Value	1,258,848
Held-to-maturity Securities, Debt Maturities, Year Six Through Ten, Fair Value	201,899
Held-to-maturity Securities, Fair Value	$ 2,157,630	$ 1,153,009
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	1.78%
Held-to-Maturity Securities, Debt Maturities, Year Two Through Five, Weighted-Average Yield	2.27%
Held-to-Maturity Securities, Debt Maturities, Weighted-Average Yield	2.66%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	$ 1,855,472
Held-to-maturity Securities, Debt Maturities, after Ten Years, Fair Value	$ 1,798,492