Farmer Mac Guaranteed Securities and USDA Securities - Schedule of Available-for-sale Securities (Details) - Farmer Mac Guaranteed Securities $ in Thousands	Sep. 30, 2020 USD ($)
Amortized Cost
Due within one year	$ 1,461,551
Due after one year through five years	3,102,003
Due after five years through ten years	1,073,248
Due after ten years	1,513,804
Amortized Cost	7,150,606
Fair Value
Due within one year	1,468,084
Due after one year through five years	3,214,595
Due after five years through ten years	1,157,450
Due after ten years	1,671,509
Total	$ 7,511,638
Weighted- Average Yield
Due within one year	1.48%
Due after one year through five years	2.24%
Due after five years through ten years	2.42%
Due after ten years	2.57%
Total	2.18%