Financial Derivatives - Schedule of Net Income/(Expense) Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income Farmer Mac Guaranteed Securities and USDA Securities	$ 85,569	$ 74,179	$ 170,980	$ 136,609
Interest Income Loans	59,403	49,396	110,800	95,049
Total Interest Expense	(122,074)	(91,737)	(236,990)	(168,054)
Gains/(losses) on financial derivatives	8,913	2,534	8,553	(1,316)
Total	31,811	34,372	53,343	62,288
Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	132,784	(10,127)	200,175	(24,511)
Gains/(losses) on fair value hedging relationships	(1,428)	1,862	(4,128)	4,701
Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	(1)	(2)	(2)	(4)
Interest settlements reclassified from AOCI into net income on derivatives	462	57	942	(210)
Recognized on hedged items	(2,697)	(2,330)	(5,417)	(4,110)
Expense recognized on cash flow hedges	(2,236)	(2,275)	(4,477)	(4,324)
Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	24,924	7,394	44,265	13,740
Discount amortization recognized on hedged items	(164)	(188)	(314)	(353)
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	8,913	2,534	8,553	(1,316)
Interest Income [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	114,638	(10,849)	173,990	(29,797)
Gains/(losses) on fair value hedging relationships	(1,767)	1,636	(1,402)	3,137
Interest Income [Member] | Cash Flow Hedging [Member]
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 [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	30,380	15,923	55,198	29,409
Discount amortization recognized on hedged items	0	0	0	0
Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	0	0	0	0
Loans and Finance Receivables [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	33,795	(2,472)	50,031	(9,045)
Gains/(losses) on fair value hedging relationships	(158)	(237)	(4,003)	(390)
Loans and Finance Receivables [Member] | Cash Flow Hedging [Member]
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
Loans and Finance Receivables [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	6,323	1,545	10,878	2,959
Discount amortization recognized on hedged items	0	0	0	0
Loans and Finance Receivables [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	0	0	0	0
Interest Expense [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(15,649)	3,194	(23,846)	14,331
Gains/(losses) on fair value hedging relationships	497	463	1,277	1,954
Interest Expense [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	(1)	(2)	(2)	(4)
Interest settlements reclassified from AOCI into net income on derivatives	462	57	942	(210)
Recognized on hedged items	(2,697)	(2,330)	(5,417)	(4,110)
Expense recognized on cash flow hedges	(2,236)	(2,275)	(4,477)	(4,324)
Interest Expense [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(11,779)	(10,074)	(21,811)	(18,628)
Discount amortization recognized on hedged items	(164)	(188)	(314)	(353)
Interest Expense [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	0	0	0	0
Gain (Loss) on Derivative Instruments [Member] | Fair Value Hedging [Member]
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
Gain (Loss) on Derivative Instruments [Member] | Cash Flow Hedging [Member]
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
Gain (Loss) on Derivative Instruments [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	0	0	0	0
Discount amortization recognized on hedged items	0	0	0	0
Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	8,913	2,534	8,553	(1,316)
Interest Rate Swap [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(1,607)	(1,804)	(3,297)	(3,884)
Income/(expense) related to interest settlements on fair value hedging relationships	23,153	5,402	40,654	9,503
Recognized on derivatives	(134,212)	11,989	(204,303)	29,212
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total Interest Expense	(1,146)	(3,869)	(3,446)	(5,855)
Gains/(losses) on financial derivatives	11,152	6,265	13,320	4,176
Interest Rate Swap [Member] | Interest Income [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	1,167	681	2,717	(807)
Income/(expense) related to interest settlements on fair value hedging relationships	31,547	16,604	57,915	28,602
Recognized on derivatives	(116,405)	12,485	(175,392)	32,934
Interest Rate Swap [Member] | Interest Income [Member] | Not Designated as Hedging Instrument [Member]
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 [Member] | Loans and Finance Receivables [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(202)	(165)	(224)	(463)
Income/(expense) related to interest settlements on fair value hedging relationships	6,121	1,380	10,654	2,496
Recognized on derivatives	(33,953)	2,235	(54,034)	8,655
Interest Rate Swap [Member] | Loans and Finance Receivables [Member] | Not Designated as Hedging Instrument [Member]
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 [Member] | Interest Expense [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(2,572)	(2,320)	(5,790)	(2,614)
Income/(expense) related to interest settlements on fair value hedging relationships	(14,515)	(12,582)	(27,915)	(21,595)
Recognized on derivatives	16,146	(2,731)	25,123	(12,377)
Interest Rate Swap [Member] | Interest Expense [Member] | Not Designated as Hedging Instrument [Member]
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 [Member] | Gain (Loss) on Derivative Instruments [Member] | Fair Value Hedging [Member]
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 [Member] | Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total Interest Expense	(1,146)	(3,869)	(3,446)	(5,855)
Gains/(losses) on financial derivatives	11,152	6,265	13,320	4,176
Future [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	(1,093)	138	(1,321)	363
Future [Member] | Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	0	0	0	0
Future [Member] | Loans and Finance Receivables [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	0	0	0	0
Future [Member] | Interest Expense [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	0	0	0	0
Future [Member] | Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives	$ (1,093)	$ 138	$ (1,321)	$ 363