Financial Derivatives - Schedule of Net Income/(Expense) Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Investments and cash equivalents	$ 4,121	$ 7,096	$ 14,107	$ 35,236
Interest Income Farmer Mac Guaranteed Securities and USDA Securities	38,428	45,335	123,246	178,644
Interest Income Loans	61,923	56,204	181,631	172,230
Total interest expense	(49,467)	(63,974)	(155,599)	(251,789)
Losses on financial derivatives	(2,347)	(564)	(1,120)	(3,339)
Total amounts presented in the consolidated statement of operations	52,658	37,001	162,265	95,746
Interest expense on interest rate swaps	1,791	2,384	11,154	8,567
Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(43,732)	(61,943)	(212,845)	323,019
Gains/(losses) on fair value hedging relationships	(1,920)	(5,047)	(3,299)	(13,109)
Cash flow hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	(11)	(4)	(25)	(6)
Interest settlements reclassified from AOCI into net income on derivatives	(1,932)	(1,814)	(5,454)	(3,817)
Recognized on hedged items	(685)	(711)	(1,983)	(3,863)
Expense recognized on cash flow hedges	(2,628)	(2,529)	(7,462)	(7,686)
Designated as hedge | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	28,088	30,076	88,670	85,495
Discount amortization recognized on hedged items	(287)	(191)	(765)	(552)
No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	(2,347)	(564)	(1,120)	(3,339)
Interest Income Investments and Cash Equivalents | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(1,737)		(1,549)
Gains/(losses) on fair value hedging relationships	90		102
Interest Income Investments and Cash Equivalents | Cash flow hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	0		0
Interest settlements reclassified from AOCI into net income on derivatives	0		0
Recognized on hedged items	0		0
Expense recognized on cash flow hedges	0		0
Interest Income Investments and Cash Equivalents | Designated as hedge | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	274		341
Discount amortization recognized on hedged items	0		0
Interest Income Investments and Cash Equivalents | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0		0
Interest Income Farmer Mac Guaranteed Securities and USDA Securities | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(31,523)	(41,855)	(150,445)	257,575
Gains/(losses) on fair value hedging relationships	(1,463)	(3,492)	(988)	(7,222)
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	28,937	31,439	90,278	95,366
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 on financial derivatives	0	0	0	0
Interest Income Loans | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(19,184)	(29,372)	(99,955)	119,072
Gains/(losses) on fair value hedging relationships	468	(1,174)	321	(5,250)
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	11,817	10,965	34,940	29,454
Discount amortization recognized on hedged items	0	0	0	0
Interest Income Loans | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0	0	0	0
Total Interest Expense | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	8,712	9,284	39,104	(53,628)
Gains/(losses) on fair value hedging relationships	(1,015)	(381)	(2,734)	(637)
Total Interest Expense | Cash flow hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	(11)	(4)	(25)	(6)
Interest settlements reclassified from AOCI into net income on derivatives	(1,932)	(1,814)	(5,454)	(3,817)
Recognized on hedged items	(685)	(711)	(1,983)	(3,863)
Expense recognized on cash flow hedges	(2,628)	(2,529)	(7,462)	(7,686)
Total Interest Expense | Designated as hedge | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(12,940)	(12,328)	(36,889)	(39,325)
Discount amortization recognized on hedged items	(287)	(191)	(765)	(552)
Total Interest Expense | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses 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
Gains/(losses) 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 on financial derivatives	(2,347)	(564)	(1,120)	(3,339)
Interest Rate Swap | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(17,091)	(16,962)	(54,150)	(34,717)
Income/(expense) related to interest settlements on fair value hedging relationships	10,710	12,923	33,755	50,226
Recognized on derivatives	41,812	56,896	209,546	(336,128)
Interest Rate Swap | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	(2,093)	(4,292)	(4,363)	(2,415)
Interest expense on interest rate swaps	168	3,800	3,489	1,143
Interest Rate Swap | Interest Income Investments and Cash Equivalents | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(141)		(177)
Income/(expense) related to interest settlements on fair value hedging relationships	133		164
Recognized on derivatives	1,827		1,651
Interest Rate Swap | Interest Income Investments and Cash Equivalents | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0		0
Interest expense on interest rate swaps	0		0
Interest Rate Swap | Interest Income Farmer Mac Guaranteed Securities and USDA Securities | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(20,925)	(20,373)	(63,966)	(38,781)
Income/(expense) related to interest settlements on fair value hedging relationships	8,012	11,066	26,312	56,585
Recognized on derivatives	30,060	38,363	149,457	(264,797)
Interest Rate Swap | Interest Income Farmer Mac Guaranteed Securities and USDA Securities | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0	0	0	0
Interest expense on interest rate swaps	0	0	0	0
Interest Rate Swap | Interest Income Loans | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(6,911)	(6,194)	(20,185)	(12,607)
Income/(expense) related to interest settlements on fair value hedging relationships	4,906	4,771	14,755	16,847
Recognized on derivatives	19,652	28,198	100,276	(124,322)
Interest Rate Swap | Interest Income Loans | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0	0	0	0
Interest expense on interest rate swaps	0	0	0	0
Interest Rate Swap | Total Interest Expense | Fair value hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	10,886	9,605	30,178	16,671
Income/(expense) related to interest settlements on fair value hedging relationships	(2,341)	(2,914)	(7,476)	(23,206)
Recognized on derivatives	(9,727)	(9,665)	(41,838)	52,991
Interest Rate Swap | Total Interest Expense | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0	0	0	0
Interest expense on interest rate swaps	0	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]
Losses on financial derivatives	(2,093)	(4,292)	(4,363)	(2,415)
Interest expense on interest rate swaps	168	3,800	3,489	1,143
Treasury futures | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	(422)	(72)	(246)	(2,067)
Treasury futures | Interest Income Investments and Cash Equivalents | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0		0
Treasury futures | Interest Income Farmer Mac Guaranteed Securities and USDA Securities | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0	0	0	0
Treasury futures | Interest Income Loans | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0	0	0	0
Treasury futures | Total Interest Expense | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0	0	0	0
Treasury futures | Losses on financial derivatives | No hedge designation
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	$ (422)	$ (72)	$ (246)	$ (2,067)