Fair Value Disclosures - Fair Value Measurements, Recurring and Nonrecurring (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets:
Financial derivatives	$ 10,167	$ 7,834
Liabilities:
Financial derivatives	171,609	105,087
Debt Securities
Assets:
Available-for-sale, at fair value	2,961,157	2,959,843
Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	7,587,352
Fair Value, Measurements, Recurring
Assets:
Available-for-sale, at fair value	2,961,157
Trading	8,408	8,913
Financial derivatives	12,692	10,519
Total Assets at fair value	10,569,443	10,122,300
Liabilities:
Financial derivatives	53,795	27,042
Total Liabilities at fair value	53,795	27,042
Fair Value, Measurements, Recurring | USDA Securities:
Assets:
Trading	8,408	8,913
Fair Value, Measurements, Recurring | Debt Securities
Assets:
Available-for-sale, at fair value		2,959,843
Fair Value, Measurements, Recurring | Level 1
Assets:
Available-for-sale, at fair value	1,155,599
Trading	0	0
Financial derivatives	0	0
Total Assets at fair value	1,155,599	1,296,923
Liabilities:
Financial derivatives	114	51
Total Liabilities at fair value	114	51
Fair Value, Measurements, Recurring | Level 1 | USDA Securities:
Assets:
Trading	0	0
Fair Value, Measurements, Recurring | Level 1 | Debt Securities
Assets:
Available-for-sale, at fair value		1,296,923
Fair Value, Measurements, Recurring | Level 2
Assets:
Available-for-sale, at fair value	1,788,837
Trading	0	0
Financial derivatives	12,692	10,519
Total Assets at fair value	1,801,529	1,654,527
Liabilities:
Financial derivatives	53,681	26,991
Total Liabilities at fair value	53,681	26,991
Fair Value, Measurements, Recurring | Level 2 | USDA Securities:
Assets:
Trading	0	0
Fair Value, Measurements, Recurring | Level 2 | Debt Securities
Assets:
Available-for-sale, at fair value		1,644,008
Fair Value, Measurements, Recurring | Level 3
Assets:
Available-for-sale, at fair value	16,721
Trading	8,408	8,913
Financial derivatives	0	0
Total Assets at fair value	7,612,315	7,170,850
Liabilities:
Financial derivatives	0	0
Total Liabilities at fair value	0	0
Fair Value, Measurements, Recurring | Level 3 | USDA Securities:
Assets:
Trading	8,408	8,913
Fair Value, Measurements, Recurring | Level 3 | Debt Securities
Assets:
Available-for-sale, at fair value		18,912
Institutional Credit | Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	7,587,186	7,143,025
Institutional Credit | Fair Value, Measurements, Recurring | Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	7,587,186	7,143,025
Institutional Credit | Fair Value, Measurements, Recurring | Level 1 | Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	0	0
Institutional Credit | Fair Value, Measurements, Recurring | Level 2 | Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	0	0
Institutional Credit | Fair Value, Measurements, Recurring | Level 3 | Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	7,587,186	7,143,025
USDA Guarantees | Fair Value, Measurements, Recurring | Farmer Mac Guaranteed Securities
Assets:
Available-for-sale, at fair value	7,587,186	7,143,025
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	7,587,186	7,143,025
Floating Interest Rate | Floating rate auction-rate certificates backed by Government guaranteed student loans
Assets:
Available-for-sale, at fair value	16,721	18,912
Floating Interest Rate | Floating rate asset-backed securities
Assets:
Available-for-sale, at fair value	10,503	11,085
Floating Interest Rate | Government/GSE Guaranteed Mortgage Backed Securities
Assets:
Available-for-sale, at fair value	1,777,999	1,632,583
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	16,721	18,912
Floating Interest Rate | Fair Value, Measurements, Recurring | Floating rate asset-backed securities
Assets:
Available-for-sale, at fair value	10,503	11,085
Floating Interest Rate | Fair Value, Measurements, Recurring | Government/GSE Guaranteed Mortgage Backed Securities
Assets:
Available-for-sale, at fair value	1,777,999	1,632,583
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 | Government/GSE 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	10,503	11,085
Floating Interest Rate | Fair Value, Measurements, Recurring | Level 2 | Government/GSE Guaranteed Mortgage Backed Securities
Assets:
Available-for-sale, at fair value	1,777,999	1,632,583
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	16,721	18,912
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 | Government/GSE Guaranteed Mortgage Backed Securities
Assets:
Available-for-sale, at fair value	0	0
Fixed Interest Rate | Government/GSE Guaranteed Mortgage Backed Securities
Assets:
Available-for-sale, at fair value	335	340
Fixed Interest Rate | Fixed rate U.S. Treasuries
Assets:
Available-for-sale, at fair value	1,155,599	1,296,923
Fixed Interest Rate | Fair Value, Measurements, Recurring | Government/GSE Guaranteed Mortgage Backed Securities
Assets:
Available-for-sale, at fair value	335	340
Fixed Interest Rate | Fair Value, Measurements, Recurring | Fixed rate U.S. Treasuries
Assets:
Available-for-sale, at fair value	1,155,599	1,296,923
Fixed Interest Rate | Fair Value, Measurements, Recurring | Level 1 | Government/GSE 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	1,155,599	1,296,923
Fixed Interest Rate | Fair Value, Measurements, Recurring | Level 2 | Government/GSE Guaranteed Mortgage Backed Securities
Assets:
Available-for-sale, at fair value	335	340
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 | Government/GSE 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