Farmer Mac Guaranteed Securities and USDA Guaranteed Securities - Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2017 USD ($) position	Dec. 31, 2016 USD ($) position
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 1,205,250	$ 1,308,744
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	530,216	564,801
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,642)	(1,844)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (6,477)	$ (7,633)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | position	96	97
Farmer Mac Guaranteed Securities and USDA Securities [Member]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 2,224,097	$ 2,205,516
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	93,978	97,270
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(69,314)	(98,996)
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(16)	(8)
Institutional Credit [Member] | Farmer Mac Guaranteed Securities [Member]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	358,636	358,575
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(3,115)	(3,175)
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,149,984	982,538
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,020,572	1,131,930
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(26,036)	(18,482)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (30,892)	$ (45,452)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | position	21	22
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | position	8	10
Held-to-maturity Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | position	7	7
USDA Guarantees [Member] | Farmer Mac Guaranteed Securities [Member]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 279	$ 30,575
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
USDA Guarantees [Member] | USDA Securities [Member]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,865,182	1,816,366
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	93,978	97,270
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(16)	(8)
Available-for-sale Securities [Member] | USDA Guarantees [Member] | Farmer Mac Guaranteed Securities [Member]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(5)	(239)
Available-for-sale Securities [Member] | USDA Guarantees [Member] | USDA Securities [Member]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (66,194)	$ (95,582)