Farmer Mac Guaranteed Securities and USDA Securities - Schedule of Held-to-maturity Securities (Details) - Farmer Mac Guaranteed Securities and USDA Securities - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Amortized Cost
Due within one year	$ 374,093
Due after one year through five years	812,373
Due after five years through ten years	260,383
Due after ten years	2,201,666
Amortized Cost	3,648,515	$ 3,649,538
Fair Value
Due within one year	376,290
Due after one year through five years	825,702
Due after five years through ten years	272,256
Due after ten years	2,318,672
Total	$ 3,792,920
Weighted- Average Yield
Due within one year	2.77%
Due after one year through five years	2.55%
Due after five years through ten years	2.79%
Due after ten years	3.13%
Total	2.92%