Financial Derivatives - Schedule of Net Income/(Expense) Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income Farmer Mac Guaranteed Securities and USDA Securities	$ 45,335	$ 81,649	$ 178,644	$ 252,629
Interest Income Loans	56,204	56,992	172,230	167,792
Total interest expense	(63,974)	(121,384)	(251,789)	(358,374)
(Losses)/gains on financial derivatives	(564)	(7,360)	(3,339)	1,193
Total	37,001	9,897	95,746	63,240
Noninterest Income	2,384	(3,295)	8,567	13,414
Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(61,943)	116,623	323,019	316,799
(Losses)/gains on fair value hedging relationships	(5,047)	(4,490)	(13,109)	(8,617)
Cash flow hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	(4)	(1)	(6)	(3)
Interest settlements reclassified from AOCI into net income on derivatives	(1,814)	317	(3,817)	1,260
Recognized on hedged items	(711)	(2,726)	(3,863)	(8,142)
Expense recognized on cash flow hedges	(2,529)	(2,410)	(7,686)	(6,885)
Designated as hedge | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	30,076	27,978	85,495	72,233
Discount amortization recognized on hedged items	191	146	552	460
No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives	(564)	(7,360)	(3,339)	1,193
Interest Income Farmer Mac Guaranteed Securities and USDA Securities | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(41,855)	84,164	257,575	258,155
(Losses)/gains on fair value hedging relationships	(3,492)	(3,331)	(7,222)	(4,731)
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 hedge | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	31,439	31,435	95,366	86,628
Discount amortization recognized on hedged items	0	0	0	0
Interest Income Farmer Mac Guaranteed Securities and USDA Securities | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives	0	0	0	0
Interest Income Loans | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(29,372)	33,493	119,072	83,524
(Losses)/gains on fair value hedging relationships	(1,174)	(2,104)	(5,250)	(6,107)
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 hedge | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	10,965	7,321	29,454	18,199
Discount amortization recognized on hedged items	0	0	0	0
Interest Income Loans | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives	0	0	0	0
Total Interest Expense | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	9,284	(1,034)	(53,628)	(24,880)
(Losses)/gains on fair value hedging relationships	(381)	945	(637)	2,221
Total Interest Expense | Cash flow hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	(4)	(1)	(6)	(3)
Interest settlements reclassified from AOCI into net income on derivatives	(1,814)	317	(3,817)	1,260
Recognized on hedged items	(711)	(2,726)	(3,863)	(8,142)
Expense recognized on cash flow hedges	(2,529)	(2,410)	(7,686)	(6,885)
Total Interest Expense | Designated as hedge | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(12,328)	(10,778)	(39,325)	(32,594)
Discount amortization recognized on hedged items	191	146	552	460
Total Interest Expense | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives	0	0	0	0
Losses 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
Losses 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
Losses on financial derivatives | Designated as hedge | 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
Losses on financial derivatives | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives	(564)	(7,360)	(3,339)	1,193
Interest Rate Swap | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(16,962)	(2,596)	(34,717)	(5,894)
Income/(expense) related to interest settlements on fair value hedging relationships	12,923	25,236	50,226	65,879
Recognized on derivatives	56,896	(121,113)	(336,128)	(325,416)
Interest Rate Swap | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Total interest expense				(3,321)
(Losses)/gains on financial derivatives	(4,292)	(7,402)	(2,415)	5,920
Noninterest Income	3,800	127	1,143
Interest Rate Swap | Interest Income Farmer Mac Guaranteed Securities and USDA Securities | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(20,373)	(1,051)	(38,781)	1,665
Income/(expense) related to interest settlements on fair value hedging relationships	11,066	30,384	56,585	88,293
Recognized on derivatives	38,363	(87,495)	(264,797)	(262,886)
Interest Rate Swap | Interest Income Farmer Mac Guaranteed Securities and USDA Securities | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Total interest expense				0
(Losses)/gains on financial derivatives	0	0	0	0
Noninterest Income	0	0	0
Interest Rate Swap | Interest Income Loans | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(6,194)	(584)	(12,607)	(808)
Income/(expense) related to interest settlements on fair value hedging relationships	4,771	6,737	16,847	17,391
Recognized on derivatives	28,198	(35,597)	(124,322)	(89,631)
Interest Rate Swap | Interest Income Loans | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Total interest expense				0
(Losses)/gains on financial derivatives	0	0	0	0
Noninterest Income	0	0	0
Interest Rate Swap | Total Interest Expense | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	9,605	(961)	16,671	(6,751)
Income/(expense) related to interest settlements on fair value hedging relationships	(2,914)	(11,885)	(23,206)	(39,805)
Recognized on derivatives	(9,665)	1,979	52,991	27,101
Interest Rate Swap | Total Interest Expense | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Total interest expense				0
(Losses)/gains on financial derivatives	0	0	0	0
Noninterest Income	0	0	0
Interest Rate Swap | Losses 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 | Losses on financial derivatives | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Total interest expense				(3,321)
(Losses)/gains on financial derivatives	(4,292)	(7,402)	(2,415)	5,920
Noninterest Income	3,800	127	1,143
Treasury futures | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives	(72)	(85)	(2,067)	(1,406)
Treasury futures | Interest Income Farmer Mac Guaranteed Securities and USDA Securities | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives	0	0	0	0
Treasury futures | Interest Income Loans | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives	0	0	0	0
Treasury futures | Total Interest Expense | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives	0	0	0	0
Treasury futures | Losses on financial derivatives | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives	$ (72)	$ (85)	$ (2,067)	$ (1,406)