Farmer Mac Guaranteed Securities and USDA Guaranteed Securities - Farmer Mac Guaranteed Securities and USDA Securities (Details) $ in Thousands	Jun. 30, 2018 USD ($) position	Dec. 31, 2017 USD ($) position
Schedule of Held-to-Maturity, Available-for-sale, and Trading Securities [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions \| position	100	91
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 2,021	$ 2,106
Farmer Mac Guaranteed Securities and USDA Securities [Member]
Schedule of Held-to-Maturity, Available-for-sale, and Trading Securities [Line Items]
Unamortized Premium/(Discount)	59,279
Held-to-Maturity Securities [Abstract]
Held-to-Maturity Unpaid Principal Balance	4,146,431	4,181,784
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	4,205,710	4,244,124
Held to Maturity; Unrealized Holding Gains	634	2,119
Held to Maturity - Unrealized Holding Loss	(97,572)	(66,471)
Held-to-maturity Securities, Fair Value	4,108,772	4,179,772
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Amortized Cost Basis	6,015,888
Available-for-sale, at fair value	5,985,806
Farmer Mac Guaranteed Securities [Member]
Schedule of Held-to-Maturity, Available-for-sale, and Trading Securities [Line Items]
Unamortized Premium/(Discount)	(120)	(460)
Held-to-Maturity Securities [Abstract]
Held-to-Maturity Unpaid Principal Balance	2,093,212	2,126,734
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	2,093,092	2,126,274
Held to Maturity; Unrealized Holding Gains	634	2,119
Held to Maturity - Unrealized Holding Loss	(19,139)	(11,502)
Held-to-maturity Securities, Fair Value	2,074,587	2,116,891
USDA Securities [Member]
Trading Securities [Abstract]
Trading, at fair value	$ 10,748	13,515
Institutional Credit [Member] \| Farmer Mac Guaranteed Securities and USDA Securities [Member]
Schedule of Held-to-Maturity, Available-for-sale, and Trading Securities [Line Items]
Unamortized Premium/(Discount)		$ 62,340
Institutional Credit [Member] \| Farmer Mac Guaranteed Securities [Member]
Schedule of Held-to-Maturity, Available-for-sale, and Trading Securities [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions \| position	46	36
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions \| position	47	23
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year \| position	16	16
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 32,910	$ 37,492
Held-to-Maturity Securities [Abstract]
Held-to-Maturity Unpaid Principal Balance	2,064,274	2,096,754
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	2,063,886	2,095,975
Held to Maturity; Unrealized Holding Gains	495	2,011
Held to Maturity - Unrealized Holding Loss	(19,139)	(11,429)
Held-to-maturity Securities, Fair Value	2,045,242	2,086,557
Available-for-sale Securities [Abstract]
Available-for-Sale Securities Unpaid Principal Balance	6,016,055	5,496,569
Available-for-sale Securities, Amortized Cost Basis	6,015,888	5,496,387
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	17,446	21,838
Available-for-sale Securities, Unrealized Losses	(47,528)	(46,311)
Available-for-sale, at fair value	5,985,806	5,471,914
Institutional Credit [Member] \| Held-to-maturity Securities [Member] \| Farmer Mac Guaranteed Securities [Member]
Schedule of Held-to-Maturity, Available-for-sale, and Trading Securities [Line Items]
Unamortized Premium/(Discount)	(388)	(779)
Institutional Credit [Member] \| Available-for-sale Securities [Member] \| Farmer Mac Guaranteed Securities [Member]
Schedule of Held-to-Maturity, Available-for-sale, and Trading Securities [Line Items]
Unamortized Premium/(Discount)	(167)	(182)
USDA Guarantees [Member]
Schedule of Held-to-Maturity, Available-for-sale, and Trading Securities [Line Items]
Unamortized Premium/(Discount)	300	300
USDA Guarantees [Member] \| Farmer Mac Guaranteed Securities [Member]
Held-to-Maturity Securities [Abstract]
Held-to-Maturity Unpaid Principal Balance	28,938	29,980
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	29,206	30,299
Held to Maturity; Unrealized Holding Gains	139	108
Held to Maturity - Unrealized Holding Loss	0	(73)
Held-to-maturity Securities, Fair Value	29,345	30,334
USDA Guarantees [Member] \| USDA Securities [Member]
Schedule of Held-to-Maturity, Available-for-sale, and Trading Securities [Line Items]
Unamortized Premium/(Discount)	59,399	62,800
Held-to-Maturity Securities [Abstract]
Held-to-Maturity Unpaid Principal Balance	2,053,219	2,055,050
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	2,112,618	2,117,850
Held to Maturity; Unrealized Holding Gains	0	0
Held to Maturity - Unrealized Holding Loss	(78,433)	(54,969)
Held-to-maturity Securities, Fair Value	2,034,185	2,062,881
Trading Securities [Abstract]
Trading Securities Unpaid Principal Balance	10,306	12,966
Trading Securities, Debt, Amortized Cost	11,094	13,888
Trading Securities, Unrealized Gains	23	28
Trading Securities, Unrealized Holding Loss	(369)	(401)
Trading, at fair value	$ 10,748	$ 13,515
Trading Securities, Weighted-Average Yield	5.26%	5.33%
USDA Guarantees [Member] \| Available-for-sale Securities [Member] \| Farmer Mac Guaranteed Securities [Member]
Schedule of Held-to-Maturity, Available-for-sale, and Trading Securities [Line Items]
Unamortized Premium/(Discount)	$ 268	$ 319
USDA Guarantees [Member] \| Trading Securities [Member] \| USDA Securities [Member]
Schedule of Held-to-Maturity, Available-for-sale, and Trading Securities [Line Items]
Unamortized Premium/(Discount)	$ 788	$ 922

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