Farmer Mac Guaranteed Securities and USDA Securities - Schedule of Held-to-maturity Securities (Details) - Farmer Mac Guaranteed Securities and USDA Securities [Member] - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Amortized Cost
Due within one year	$ 682,586
Due after one year through five years	1,420,155
Due after five years through ten years	204,350
Due after ten years	1,858,636
Amortized Cost	4,165,727	$ 4,262,792
Fair Value
Due within one year	681,561
Due after one year through five years	1,421,423
Due after five years through ten years	202,025
Due after ten years	1,840,650
Total	$ 4,145,659	$ 4,191,352
Weighted- Average Yield
Due within one year	2.15%
Due after one year through five years	3.07%
Due after five years through ten years	3.45%
Due after ten years	3.62%
Total	3.18%