Fair Value Disclosures - Fair Value Measurements, Recurring and Nonrecurring (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Assets:
Financial derivatives	$ 12,237,000	$ 7,834,000
Loans held for sale	20,000,000	0
Liabilities:
Financial derivatives	188,289,000	105,087,000
Investment securities
Assets:
Available-for-sale, at fair value	3,532,190,000	2,959,843,000
Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	7,511,638,000
Fair Value, Measurements, Recurring
Assets:
Trading	6,830,000	8,913,000
Financial derivatives	12,837,000	10,519,000
Total Assets at fair value	11,063,495,000	10,122,300,000
Liabilities:
Financial derivatives	37,357,000	27,042,000
Total Liabilities at fair value	37,357,000	27,042,000
Fair Value, Measurements, Recurring \| USDA Securities:
Assets:
Trading	6,830,000	8,913,000
Fair Value, Measurements, Recurring \| Investment securities
Assets:
Available-for-sale, at fair value	3,532,190,000	2,959,843,000
Fair Value, Measurements, Recurring \| Level 1
Assets:
Trading	0	0
Financial derivatives	9,000	0
Total Assets at fair value	1,217,575,000	1,296,923,000
Liabilities:
Financial derivatives	0	51,000
Total Liabilities at fair value	0	51,000
Fair Value, Measurements, Recurring \| Level 1 \| USDA Securities:
Assets:
Trading	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Investment securities
Assets:
Available-for-sale, at fair value	1,217,566,000	1,296,923,000
Fair Value, Measurements, Recurring \| Level 2
Assets:
Trading	0	0
Financial derivatives	12,828,000	10,519,000
Total Assets at fair value	2,308,380,000	1,654,527,000
Liabilities:
Financial derivatives	37,357,000	26,991,000
Total Liabilities at fair value	37,357,000	26,991,000
Fair Value, Measurements, Recurring \| Level 2 \| USDA Securities:
Assets:
Trading	0	0
Fair Value, Measurements, Recurring \| Level 2 \| Investment securities
Assets:
Available-for-sale, at fair value	2,295,552,000	1,644,008,000
Fair Value, Measurements, Recurring \| Level 3
Assets:
Trading	6,830,000	8,913,000
Financial derivatives	0	0
Total Assets at fair value	7,537,540,000	7,170,850,000
Liabilities:
Financial derivatives	0	0
Total Liabilities at fair value	0	0
Fair Value, Measurements, Recurring \| Level 3 \| USDA Securities:
Assets:
Trading	6,830,000	8,913,000
Fair Value, Measurements, Recurring \| Level 3 \| Investment securities
Assets:
Available-for-sale, at fair value	19,072,000	18,912,000
Fair Value, Nonrecurring
Assets:
Loans held for sale	22,086,000
Total Assets at fair value	22,086,000
Fair Value, Nonrecurring \| Level 1
Assets:
Loans held for sale	0
Total Assets at fair value	0
Fair Value, Nonrecurring \| Level 2
Assets:
Loans held for sale	0
Total Assets at fair value	0
Fair Value, Nonrecurring \| Level 3
Assets:
Loans held for sale	22,086,000
Total Assets at fair value	22,086,000
AgVantage Securities \| Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	7,511,638,000	7,143,025,000
AgVantage Securities \| Fair Value, Measurements, Recurring \| Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	7,511,638,000	7,143,025,000
AgVantage Securities \| Fair Value, Measurements, Recurring \| Level 1 \| Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	0	0
AgVantage Securities \| Fair Value, Measurements, Recurring \| Level 2 \| Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	0	0
AgVantage Securities \| Fair Value, Measurements, Recurring \| Level 3 \| Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	7,511,638,000	7,143,025,000
USDA Guarantees \| Fair Value, Measurements, Recurring \| Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	7,511,638,000	7,143,025,000
USDA Guarantees \| Fair Value, Measurements, Recurring \| Level 1 \| Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	0	0
USDA Guarantees \| Fair Value, Measurements, Recurring \| Level 2 \| Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	0	0
USDA Guarantees \| Fair Value, Measurements, Recurring \| Level 3 \| Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	7,511,638,000	7,143,025,000
Floating Interest Rate \| Floating rate auction-rate certificates backed by Government guaranteed student loans
Assets:
Available-for-sale, at fair value	19,072,000	18,912,000
Floating Interest Rate \| Floating rate asset-backed securities
Assets:
Available-for-sale, at fair value	9,201,000	11,085,000
Floating Interest Rate \| Guaranteed mortgage-backed securities
Assets:
Available-for-sale, at fair value	2,286,033,000	1,632,583,000
Floating Interest Rate \| Fair Value, Measurements, Recurring \| Floating rate auction-rate certificates backed by Government guaranteed student loans
Assets:
Available-for-sale, at fair value	19,072,000	18,912,000
Floating Interest Rate \| Fair Value, Measurements, Recurring \| Floating rate asset-backed securities
Assets:
Available-for-sale, at fair value	9,201,000	11,085,000
Floating Interest Rate \| Fair Value, Measurements, Recurring \| Guaranteed mortgage-backed securities
Assets:
Available-for-sale, at fair value	2,286,033,000	1,632,583,000
Floating Interest Rate \| Fair Value, Measurements, Recurring \| Level 1 \| Floating rate auction-rate certificates backed by Government guaranteed student loans
Assets:
Available-for-sale, at fair value	0	0
Floating Interest Rate \| Fair Value, Measurements, Recurring \| Level 1 \| Floating rate asset-backed securities
Assets:
Available-for-sale, at fair value	0	0
Floating Interest Rate \| Fair Value, Measurements, Recurring \| Level 1 \| Guaranteed mortgage-backed securities
Assets:
Available-for-sale, at fair value	0	0
Floating Interest Rate \| Fair Value, Measurements, Recurring \| Level 2 \| Floating rate auction-rate certificates backed by Government guaranteed student loans
Assets:
Available-for-sale, at fair value	0	0
Floating Interest Rate \| Fair Value, Measurements, Recurring \| Level 2 \| Floating rate asset-backed securities
Assets:
Available-for-sale, at fair value	9,201,000	11,085,000
Floating Interest Rate \| Fair Value, Measurements, Recurring \| Level 2 \| Guaranteed mortgage-backed securities
Assets:
Available-for-sale, at fair value	2,286,033,000	1,632,583,000
Floating Interest Rate \| Fair Value, Measurements, Recurring \| Level 3 \| Floating rate auction-rate certificates backed by Government guaranteed student loans
Assets:
Available-for-sale, at fair value	19,072,000	18,912,000
Floating Interest Rate \| Fair Value, Measurements, Recurring \| Level 3 \| Floating rate asset-backed securities
Assets:
Available-for-sale, at fair value	0	0
Floating Interest Rate \| Fair Value, Measurements, Recurring \| Level 3 \| Guaranteed mortgage-backed securities
Assets:
Available-for-sale, at fair value	0	0
Fixed Interest Rate \| Guaranteed mortgage-backed securities
Assets:
Available-for-sale, at fair value	318,000	340,000
Fixed Interest Rate \| Fixed rate U.S. Treasuries
Assets:
Available-for-sale, at fair value	1,217,566,000	1,296,923,000
Fixed Interest Rate \| Fair Value, Measurements, Recurring \| Guaranteed mortgage-backed securities
Assets:
Available-for-sale, at fair value	318,000	340,000
Fixed Interest Rate \| Fair Value, Measurements, Recurring \| Fixed rate U.S. Treasuries
Assets:
Available-for-sale, at fair value	1,217,566,000	1,296,923,000
Fixed Interest Rate \| Fair Value, Measurements, Recurring \| Level 1 \| Guaranteed mortgage-backed securities
Assets:
Available-for-sale, at fair value	0	0
Fixed Interest Rate \| Fair Value, Measurements, Recurring \| Level 1 \| Fixed rate U.S. Treasuries
Assets:
Available-for-sale, at fair value	1,217,566,000	1,296,923,000
Fixed Interest Rate \| Fair Value, Measurements, Recurring \| Level 2 \| Guaranteed mortgage-backed securities
Assets:
Available-for-sale, at fair value	318,000	340,000
Fixed Interest Rate \| Fair Value, Measurements, Recurring \| Level 2 \| Fixed rate U.S. Treasuries
Assets:
Available-for-sale, at fair value	0	0
Fixed Interest Rate \| Fair Value, Measurements, Recurring \| Level 3 \| Guaranteed mortgage-backed securities
Assets:
Available-for-sale, at fair value	0	0
Fixed Interest Rate \| Fair Value, Measurements, Recurring \| Level 3 \| Fixed rate U.S. Treasuries
Assets:
Available-for-sale, at fair value	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value of financial and nonfinancial obligations.

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