Farmer Mac Guaranteed Securities and USDA Guaranteed Securities - Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2018 USD ($) position	Dec. 31, 2017 USD ($) position
Debt Securities, Available-for-sale, Unrealized Loss Position [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 1,433,453	$ 1,034,964
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	315,786	388,534
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(3,281)	(3,909)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(2,647)	(2,106)
Farmer Mac Guaranteed Securities and USDA Securities [Member]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	707,813	1,329,332
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	3,042,061	2,414,093
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(2,456)	(8,169)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(71,719)	(58,302)
Institutional Credit [Member] | Farmer Mac Guaranteed Securities [Member]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	669,610	1,304,160
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	976,318	351,664
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,760)	(8,094)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(10,188)	(3,335)
Debt Securities, Available-for-sale, Unrealized Loss Position [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,480,423	1,273,965
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,599,679	1,759,377
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(9,364)	(8,819)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (42,003)	$ (37,492)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Number of Positions [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | position	38	36
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | position	43	23
USDA Guarantees [Member] | Farmer Mac Guaranteed Securities [Member]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value		$ 24,721
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value		0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
USDA Guarantees [Member] | USDA Securities [Member]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 38,203	451
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	2,065,743	2,062,429
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(61,531)	(54,967)
Available-for-sale Securities [Member] | USDA Guarantees [Member] | Farmer Mac Guaranteed Securities [Member]
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(73)
Available-for-sale Securities [Member] | USDA Guarantees [Member] | USDA Securities [Member]
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (696)	$ (2)