Fair Value Disclosures - Quantitative Information (Details) - Recurring - Level 3 $ in Thousands	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 6,163,052	$ 6,901,703	$ 6,973,567	$ 7,537,540	$ 7,924,456	$ 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	19,500		19,171
USDA Securities:
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	4,793	$ 5,050	6,695	$ 6,830	$ 7,786	$ 8,913
AgVantage Securities | Farmer Mac Guaranteed Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 6,138,759		$ 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	0.993		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	0.993		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	0.993		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	0.009		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	0.014		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	0.021		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	0.023		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	0.014		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	0.018		0.014
CPR | Minimum | USDA Guarantees | USDA Securities: | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.25		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	0.34		0.44