Farmer Mac Guaranteed Securities and USDA Securities - Schedule of Held-to-maturity Securities (Details) - Farmer Mac Guaranteed Securities and USDA Securities - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Amortized Cost
Due within one year	$ 526,374
Due after one year through five years	683,135
Due after five years through ten years	255,180
Due after ten years	2,184,849
Amortized Cost	3,649,538	$ 3,679,611
Fair Value
Due within one year	529,401
Due after one year through five years	706,287
Due after five years through ten years	269,945
Due after ten years	2,326,171
Total	$ 3,831,804	$ 3,749,184
Weighted- Average Yield
Due within one year	2.79%
Due after one year through five years	3.12%
Due after five years through ten years	2.89%
Due after ten years	3.19%
Total	3.07%