Fair Value Disclosures - Quantitative Information (Details) - Recurring - Level 3 $ in Thousands	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 6,787,933	$ 6,973,567	$ 7,612,315	$ 7,170,850
Floating rate auction-rate certificates backed by Government guaranteed student loans | Floating Interest Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	19,146	19,171
USDA Securities:
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	5,578	6,695	$ 8,408	$ 8,913
AgVantage Securities | Farmer Mac Guaranteed Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 6,763,209	$ 6,947,701
Range of broker quotes | Minimum | Floating rate auction-rate certificates backed by Government guaranteed student loans | Indicative bids
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.975	0.975
Range of broker quotes | Maximum | Floating rate auction-rate certificates backed by Government guaranteed student loans | Indicative bids
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.975	0.975
Range of broker quotes | Weighted Average | Floating rate auction-rate certificates backed by Government guaranteed student loans | Indicative bids
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.975	0.975
Discount rate | Minimum | AgVantage Securities | Farmer Mac Guaranteed Securities | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.008	0.008
Discount rate | Minimum | USDA Guarantees | USDA Securities: | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.011	0.009
Discount rate | Maximum | AgVantage Securities | Farmer Mac Guaranteed Securities | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.027	0.023
Discount rate | Maximum | USDA Guarantees | USDA Securities: | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.018	0.019
Discount rate | Weighted Average | AgVantage Securities | Farmer Mac Guaranteed Securities | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.015	0.013
Discount rate | Weighted Average | USDA Guarantees | USDA Securities: | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.014	0.014
CPR | Minimum | USDA Guarantees | USDA Securities: | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.23	0.25
CPR | Maximum | USDA Guarantees | USDA Securities: | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.43	0.49
CPR | Weighted Average | USDA Guarantees | USDA Securities: | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.33	0.44