Farmer Mac Guaranteed Securities and USDA Securities - Schedule of Available-for-sale Securities (Details) - Farmer Mac Guaranteed Securities [Member] $ in Thousands	Sep. 30, 2019 USD ($)
Amortized Cost
Due within one year	$ 560,697
Due after one year through five years	3,637,536
Due after five years through ten years	1,262,707
Due after ten years	1,547,945
Amortized Cost	7,008,885
Fair Value
Due within one year	559,763
Due after one year through five years	3,690,151
Due after five years through ten years	1,308,724
Due after ten years	1,623,903
Total	$ 7,182,541
Weighted- Average Yield
Due within one year	2.47%
Due after one year through five years	3.01%
Due after five years through ten years	3.10%
Due after ten years	3.40%
Total	3.07%