Financial Derivatives - Schedule of Net Income/(Expense) Recognized (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income Farmer Mac Guaranteed Securities and USDA Securities	$ 85,411	$ 62,430
Interest Income Loans	51,397	45,653
Total Interest Expense	(114,916)	(76,317)
Losses on financial derivatives	(360)	(3,850)
Total	21,532	27,916
Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	67,392	(14,383)
Gains/(losses) on fair value hedging relationships	(2,699)	2,838
Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	(1)	(2)
Interest settlements reclassified from AOCI into net income on derivatives	481	(267)
Recognized on hedged items	(2,688)	(1,780)
Expense recognized on cash flow hedges	(2,208)	(2,049)
Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	19,198	7,096
Discount amortization recognized on hedged items	(149)	(155)
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	(360)	(3,850)
Interest Income [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	59,352	(18,948)
Gains/(losses) on fair value hedging relationships	365	1,501
Interest Income [Member] | Cash Flow Hedging [Member]
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 [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	24,565	13,597
Discount amortization recognized on hedged items	0	0
Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0	0
Loans and Finance Receivables [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	16,237	(6,572)
Gains/(losses) on fair value hedging relationships	(3,845)	(153)
Loans and Finance Receivables [Member] | Cash Flow Hedging [Member]
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
Loans and Finance Receivables [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	4,555	1,414
Discount amortization recognized on hedged items	0	0
Loans and Finance Receivables [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0	0
Interest Expense [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(8,197)	11,137
Gains/(losses) on fair value hedging relationships	781	1,490
Interest Expense [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Discount amortization recognized on hedged items	(1)	(2)
Interest settlements reclassified from AOCI into net income on derivatives	481	(267)
Recognized on hedged items	(2,688)	(1,780)
Expense recognized on cash flow hedges	(2,208)	(2,049)
Interest Expense [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	(9,922)	(7,915)
Discount amortization recognized on hedged items	(149)	(155)
Interest Expense [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0	0
Gain (Loss) on Derivative Instruments [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on hedged items	0	0
Gains/(losses) on fair value hedging relationships	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
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
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
Discount amortization recognized on hedged items	0	0
Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	(360)	(3,850)
Interest Rate Swap [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(1,690)	(1,491)
Income/(expense) related to interest settlements on fair value hedging relationships	17,359	5,450
Recognized on derivatives	(70,091)	17,221
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total Interest Expense	(2,300)	(1,987)
Losses on financial derivatives	2,168	(2,088)
Interest Rate Swap [Member] | Interest Income [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	1,550	(1,488)
Income/(expense) related to interest settlements on fair value hedging relationships	26,115	12,109
Recognized on derivatives	(58,987)	20,449
Interest Rate Swap [Member] | Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total Interest Expense	0	0
Losses on financial derivatives	0	0
Interest Rate Swap [Member] | Loans and Finance Receivables [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(22)	(297)
Income/(expense) related to interest settlements on fair value hedging relationships	4,533	1,117
Recognized on derivatives	(20,082)	6,419
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
Losses on financial derivatives	0	0
Interest Rate Swap [Member] | Interest Expense [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(3,218)	294
Income/(expense) related to interest settlements on fair value hedging relationships	(13,289)	(7,776)
Recognized on derivatives	8,978	(9,647)
Interest Rate Swap [Member] | Interest Expense [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total Interest Expense	0	0
Losses on financial derivatives	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
Income/(expense) related to interest settlements on fair value hedging relationships	0	0
Recognized on derivatives	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	(2,300)	(1,987)
Losses on financial derivatives	2,168	(2,088)
Future [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	(228)	225
Future [Member] | Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0	0
Future [Member] | Loans and Finance Receivables [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0	0
Future [Member] | Interest Expense [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	0	0
Future [Member] | Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	$ (228)	$ 225