Financial Derivatives - Schedule of Net Income/(Expense) Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income Farmer Mac Guaranteed Securities and USDA Securities	$ 61,792	$ 85,569	$ 133,309	$ 170,980
Interest Income Loans	55,430	59,403	116,026	110,800
Total Interest Expense	(79,273)	(122,074)	(187,815)	(236,990)
Gains/(losses) on financial derivatives	6,523	8,913	(2,775)	8,553
Total	44,472	31,811	58,745	53,343
Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	9,739	132,784	384,962	200,175
(Losses)/gains on fair value hedging relationships	(2,381)	(1,428)	(8,062)	(4,128)
Cash flow hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	(2)	(1)	(2)	(2)
Interest settlements reclassified from AOCI into net income on derivatives	(1,563)	462	(2,002)	942
Recognized on hedged items	(1,029)	(2,697)	(3,152)	(5,417)
Expense recognized on cash flow hedges	(2,594)	(2,236)	(5,156)	(4,477)
Designated as Hedging Instrument | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	29,193	24,924	55,419	44,265
Discount amortization recognized on hedged items	(181)	(164)	(361)	(314)
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	6,523	8,913	(2,775)	8,553
Interest Income Farmer Mac Guaranteed Securities and USDA Securities | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	9,050	114,638	299,430	173,990
(Losses)/gains on fair value hedging relationships	(176)	(1,767)	(3,729)	(1,402)
Interest Income Farmer Mac Guaranteed Securities and USDA Securities | Cash flow hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	0	0	0	0
Interest settlements reclassified from AOCI into net income on derivatives	0	0	0	0
Recognized on hedged items	0	0	0	0
Expense recognized on cash flow hedges	0	0	0	0
Interest Income Farmer Mac Guaranteed Securities and USDA Securities | Designated as Hedging Instrument | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	32,102	30,380	63,927	55,198
Discount amortization recognized on hedged items	0	0	0	0
Interest Income Farmer Mac Guaranteed Securities and USDA Securities | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	0	0	0	0
Interest Income Loans | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	3,037	33,795	148,445	50,031
(Losses)/gains on fair value hedging relationships	(3,579)	(158)	(4,076)	(4,003)
Interest Income Loans | Cash flow hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	0	0	0	0
Interest settlements reclassified from AOCI into net income on derivatives	0	0	0	0
Recognized on hedged items	0	0	0	0
Expense recognized on cash flow hedges	0	0	0	0
Interest Income Loans | Designated as Hedging Instrument | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	9,812	6,323	18,489	10,878
Discount amortization recognized on hedged items	0	0	0	0
Interest Income Loans | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	0	0	0	0
Total Interest Expense | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(2,348)	(15,649)	(62,913)	(23,846)
(Losses)/gains on fair value hedging relationships	1,374	497	(257)	1,277
Total Interest Expense | Cash flow hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	(2)	(1)	(2)	(2)
Interest settlements reclassified from AOCI into net income on derivatives	(1,563)	462	(2,002)	942
Recognized on hedged items	(1,029)	(2,697)	(3,152)	(5,417)
Expense recognized on cash flow hedges	(2,594)	(2,236)	(5,156)	(4,477)
Total Interest Expense | Designated as Hedging Instrument | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(12,721)	(11,779)	(26,997)	(21,811)
Discount amortization recognized on hedged items	(181)	(164)	(361)	(314)
Total Interest Expense | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	0	0	0	0
Gains on financial derivatives | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	0	0	0	0
(Losses)/gains on fair value hedging relationships	0	0	0	0
Gains on financial derivatives | Cash flow hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	0	0	0	0
Interest settlements reclassified from AOCI into net income on derivatives	0	0	0	0
Recognized on hedged items	0	0	0	0
Expense recognized on cash flow hedges	0	0	0	0
Gains on financial derivatives | Designated as Hedging Instrument | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	0	0	0	0
Discount amortization recognized on hedged items	0	0	0	0
Gains on financial derivatives | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	6,523	8,913	(2,775)	8,553
Interest Rate Swap | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(11,360)	(1,607)	(17,754)	(3,297)
Income/(expense) related to interest settlements on fair value hedging relationships	17,652	23,153	37,304	40,654
Recognized on derivatives	(12,120)	(134,212)	(393,024)	(204,303)
Interest Rate Swap | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Total Interest Expense	(1,795)	(1,146)	(2,657)	(3,446)
Gains/(losses) on financial derivatives	8,427	11,152	1,878	13,320
Interest Rate Swap | Interest Income Farmer Mac Guaranteed Securities and USDA Securities | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(12,257)	1,167	(18,408)	2,717
Income/(expense) related to interest settlements on fair value hedging relationships	19,845	31,547	45,519	57,915
Recognized on derivatives	(9,226)	(116,405)	(303,159)	(175,392)
Interest Rate Swap | Interest Income Farmer Mac Guaranteed Securities and USDA Securities | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Total Interest Expense	0	0	0	0
Gains/(losses) on financial derivatives	0	0	0	0
Interest Rate Swap | Interest Income Loans | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(4,535)	(202)	(6,412)	(224)
Income/(expense) related to interest settlements on fair value hedging relationships	5,277	6,121	12,077	10,654
Recognized on derivatives	(6,616)	(33,953)	(152,521)	(54,034)
Interest Rate Swap | Interest Income Loans | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Total Interest Expense	0	0	0	0
Gains/(losses) on financial derivatives	0	0	0	0
Interest Rate Swap | Total Interest Expense | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	5,432	(2,572)	7,066	(5,790)
Income/(expense) related to interest settlements on fair value hedging relationships	(7,470)	(14,515)	(20,292)	(27,915)
Recognized on derivatives	3,722	16,146	62,656	25,123
Interest Rate Swap | Total Interest Expense | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Total Interest Expense	0	0	0	0
Gains/(losses) on financial derivatives	0	0	0	0
Interest Rate Swap | Gains on financial derivatives | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	0	0	0	0
Income/(expense) related to interest settlements on fair value hedging relationships	0	0	0	0
Recognized on derivatives	0	0	0	0
Interest Rate Swap | Gains on financial derivatives | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Total Interest Expense	(1,795)	(1,146)	(2,657)	(3,446)
Gains/(losses) on financial derivatives	8,427	11,152	1,878	13,320
Treasury futures | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	(109)	(1,093)	(1,996)	(1,321)
Treasury futures | Interest Income Farmer Mac Guaranteed Securities and USDA Securities | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	0	0	0	0
Treasury futures | Interest Income Loans | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	0	0	0	0
Treasury futures | Total Interest Expense | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	0	0	0	0
Treasury futures | Gains on financial derivatives | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	$ (109)	$ (1,093)	$ (1,996)	$ (1,321)