Farmer Mac Guaranteed Securities and USDA Securities - Schedule of Held-to-maturity Securities (Details) - Farmer Mac Guaranteed Securities and USDA Securities - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Due within one year	$ 482,593
Due after one year through five years	765,529
Due after five years through ten years	226,396
Due after ten years	2,137,116
Amortized Cost	3,611,634	$ 3,679,611
Fair Value
Due within one year	486,460
Due after one year through five years	790,138
Due after five years through ten years	234,799
Due after ten years	2,231,239
Total	$ 3,742,636	$ 3,749,184
Weighted- Average Yield
Due within one year	2.75%
Due after one year through five years	3.15%
Due after five years through ten years	2.96%
Due after ten years	3.25%
Total	3.11%