Fair Value Disclosures - Unobservable Input Reconciliation (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands		3 Months Ended			12 Months Ended
		Dec. 31, 2014		Mar. 31, 2014	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				$ (235)	$ 0		$ (235)		$ (691)
Purchases							0		0
Sales							0		0
Settlements							0		0
Realized and Unrealized Gains/(Losses) included in Income							235		456
Unrealized Gains/(Losses) included in Other Comprehen-sive Income							0		0
Transfers Out							0
Ending Balance		$ 0					0		(235)
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				6,770,031	5,472,078		6,770,031		6,421,447
Purchases					1,055,501		1,434,461		1,635,627
Sales					0		(26,675)		0
Settlements					(394,307)		(1,153,191)		(1,129,054)
Realized and Unrealized Gains/(Losses) included in Income					4,210		15,292		(19,049)
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					(22,143)		64,946		(138,940)
Transfers Out							(1,632,786)
Ending Balance		5,472,078			6,115,339		5,472,078		6,770,031
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance									(691)
Investment Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				66,418	41,265		66,418		64,406
Purchases					0		0		233
Sales					0		(26,675)		0
Settlements					(657)		(890)		(798)
Realized and Unrealized Gains/(Losses) included in Income					359		(379)		455
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					4,448		2,791		2,122
Transfers Out							0
Ending Balance		41,265			45,415		41,265		66,418
USDA Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Trading Securities, Unrealized Gains					900		1,800		500
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				1,612,013	1,771,532		1,612,013		1,590,783
Purchases					363,621		335,359		361,894
Sales					0		0		0
Settlements					(245,481)		(228,585)		(278,605)
Realized and Unrealized Gains/(Losses) included in Income					761		1,151		(1,274)
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					26,886		51,594		(60,785)
Transfers Out							0
Ending Balance		1,771,532			1,917,319		1,771,532		1,612,013
Available-for-sale Securities [Member] | Investment Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				65,490	40,576		65,490		63,159
Purchases					0		0		233
Sales					0		(26,675)		0
Settlements					0		(205)		(24)
Realized and Unrealized Gains/(Losses) included in Income					(100)		(825)		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					4,448		2,791		2,122
Transfers Out							0
Ending Balance		40,576			44,924		40,576		65,490
Available-for-sale Securities [Member] | Farmer Mac Guaranteed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				5,091,600	3,659,281		5,091,600		4,766,258
Purchases					691,880		1,099,102		1,273,500
Sales					0		0		0
Settlements					(148,169)		(923,716)		(849,651)
Realized and Unrealized Gains/(Losses) included in Income					3,090		14,520		(18,230)
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					(53,477)		10,561		(80,277)
Transfers Out							(1,632,786)
Ending Balance		3,659,281			4,152,605		3,659,281		5,091,600
Available-for-sale Securities [Member] | USDA Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				1,553,669	1,731,222		1,553,669		1,486,595
Purchases					363,621		335,359		361,894
Sales					0		0		0
Settlements					(233,385)		(209,400)		(234,035)
Realized and Unrealized Gains/(Losses) included in Income					0		0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					26,886		51,594		(60,785)
Transfers Out							0
Ending Balance		1,731,222			1,888,344		1,731,222		1,553,669
Trading Securities [Member] | Investment Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				928	689		928		1,247
Purchases					0		0		0
Sales					0		0		0
Settlements					(657)		(685)		(774)
Realized and Unrealized Gains/(Losses) included in Income					459		446		455
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					0		0		0
Transfers Out							0
Ending Balance		689			491		689		928
Trading Securities [Member] | USDA Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				58,344	40,310		58,344		104,188
Purchases					0		0		0
Sales					0		0		0
Settlements					(12,096)		(19,185)		(44,570)
Realized and Unrealized Gains/(Losses) included in Income					761		1,151		(1,274)
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					0		0		0
Transfers Out							0
Ending Balance		40,310			28,975		40,310		58,344
Institutional Credit [Member] | Available-for-sale Securities [Member] | Farmer Mac Guaranteed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				5,070,366	3,631,662	[1]	5,070,366		4,739,577
Purchases					678,566	[1]	1,091,475		1,273,500
Sales					0	[1]	0		0
Settlements					(138,687)	[1]	(922,908)		(844,437)
Realized and Unrealized Gains/(Losses) included in Income					3,090	[1]	14,520		(18,230)
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					(53,387)	[1]	10,995		(80,044)
Transfers Out		0		(1,600,000)	0		(1,632,786)		0
Ending Balance		3,631,662	[1]		4,121,244	[1]	3,631,662	[1]	5,070,366
USDA Guarantees [Member] | Available-for-sale Securities [Member] | Farmer Mac Guaranteed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				21,234	27,619		21,234		26,681
Purchases					13,314		7,627		0
Sales					0		0		0
Settlements					(9,482)		(808)		(5,214)
Realized and Unrealized Gains/(Losses) included in Income					0		0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					(90)		(434)		(233)
Transfers Out							0
Ending Balance		27,619			31,361		27,619		21,234
Floating Interest Rate [Member] | Available-for-sale Securities [Member] | Floating rate auction-rate certificates backed by Government guaranteed student loans | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				65,285	40,576		65,285		63,159
Purchases					0		0		0
Sales					0		(26,675)		0
Settlements					0		0		0
Realized and Unrealized Gains/(Losses) included in Income					(100)		(825)		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					4,448		2,791		2,126
Transfers Out							0
Ending Balance		40,576			44,924		40,576		65,285
Floating Interest Rate [Member] | Available-for-sale Securities [Member] | Farmer Mac Guaranteed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				205	0		205		0
Purchases							0		233
Sales							0		0
Settlements							(205)		(24)
Realized and Unrealized Gains/(Losses) included in Income							0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income							0		(4)
Transfers Out							0
Ending Balance		0					0		205
Floating Interest Rate [Member] | Trading Securities [Member] | Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	[2]			$ 928	689		928		1,247
Purchases	[2]				0		0		0
Sales	[2]				0		0		0
Settlements	[2]				(657)		(685)		(774)
Realized and Unrealized Gains/(Losses) included in Income	[2]				459		446		455
Unrealized Gains/(Losses) included in Other Comprehen-sive Income	[2]				0		0		0
Transfers Out	[2]						0
Ending Balance	[2]	$ 689			$ 491		$ 689		$ 928

[1] Includes unrealized gains of $0.9 million attributable to assets still held as of December 31, 2015 that are recorded in "Gains/(losses) on trading securities."

[2] Unrealized gains are attributable to assets still held as of December 31, 2015 and are recorded in "Gains/(losses) on trading securities."