Farmer Mac Guaranteed Securities and USDA Securities - Schedule of Available-for-sale Securities (Details) - Farmer Mac Guaranteed Securities [Member] $ in Thousands	Mar. 31, 2019 USD ($)
Amortized Cost
Due within one year	$ 584,884
Due after one year through five years	2,976,650
Due after five years through ten years	1,281,673
Due after ten years	1,564,921
Amortized Cost	6,408,128
Fair Value
Due within one year	585,085
Due after one year through five years	2,988,640
Due after five years through ten years	1,291,943
Due after ten years	1,575,956
Total	$ 6,441,624
Weighted- Average Yield
Due within one year	3.09%
Due after one year through five years	3.16%
Due after five years through ten years	3.21%
Due after ten years	3.62%
Total	3.28%