Farmer Mac Guaranteed Securities and USDA Guaranteed Securities - Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2015 USD ($) position	Dec. 31, 2014 USD ($) 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	$ 313,800	$ 495,501
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	184,871	183,763
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	985	228
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 6,166	$ 9,983
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	44	35
Farmer Mac Guaranteed Securities and USDA Securities [Member]
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	$ 1,589,294	$ 953,226
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	944,002	1,557,906
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	57,167	14,671
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	18,251	16,792
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		547
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		49,745
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		(1)
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		(254)
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	1,560,161	685,131
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	843,727	1,460,089
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	56,977	13,115
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 17,900	$ 16,738
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	24	23
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | position	6	15
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	0	2
USDA Guarantees [Member] | Farmer Mac Guaranteed Securities [Member]
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	$ 29,133	$ 3,720
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
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	190	7
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
USDA Guarantees [Member] | USDA Securities [Member]
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	0	264,375
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	100,275	97,817
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	0	1,549
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 351	$ 54