Fair Value Disclosures - Quantitative Information (Details) - Fair Value, Measurements, Recurring - Fair Value, Inputs, Level 3 $ in Thousands	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 7,170,850	$ 6,003,211	$ 5,508,576	$ 4,891,803
USDA Securities:
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	8,913	9,999	13,515	20,388
Available-for-Sale Securities | Farmer Mac Guaranteed Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	7,143,025	5,974,497	5,471,914	4,853,685
Available-for-Sale Securities | USDA Securities:
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	0	0	0	0
Available-for-Sale Securities | Institutional Credit | Farmer Mac Guaranteed Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	7,143,025	5,974,497	5,471,914	4,853,685
Trading Securities | USDA Securities:
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 8,913	$ 9,999	$ 13,515	$ 20,388
Measurement Input, Discount Rate | Minimum | Institutional Credit | Farmer Mac Guaranteed Securities | Valuation, Cost Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.023	0.030
Measurement Input, Discount Rate | Minimum | USDA Guarantees | USDA Securities: | Valuation, Cost Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.023	0.032
Measurement Input, Discount Rate | Maximum | Institutional Credit | Farmer Mac Guaranteed Securities | Valuation, Cost Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.055	0.044
Measurement Input, Discount Rate | Maximum | USDA Guarantees | USDA Securities: | Valuation, Cost Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.026	0.052
Measurement Input, Discount Rate | Weighted Average | Institutional Credit | Farmer Mac Guaranteed Securities | Valuation, Cost Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.026	0.033
Measurement Input, Discount Rate | Weighted Average | USDA Guarantees | USDA Securities: | Valuation, Cost Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.021	0.049
Measurement Input, Constant Prepayment Rate | Minimum | USDA Guarantees | USDA Securities: | Valuation, Cost Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.10	0.07
Measurement Input, Constant Prepayment Rate | Maximum | USDA Guarantees | USDA Securities: | Valuation, Cost Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.21	0.17
Measurement Input, Constant Prepayment Rate | Weighted Average | USDA Guarantees | USDA Securities: | Valuation, Cost Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.19	0.16
Measurement Input, Range of Broker Quotes | Minimum | Floating rate auction-rate certificates backed by Government guaranteed student loans | Valuation, Market Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.960	0.950
Measurement Input, Range of Broker Quotes | Maximum | Floating rate auction-rate certificates backed by Government guaranteed student loans | Valuation, Market Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.960	0.950
Measurement Input, Range of Broker Quotes | Weighted Average | Floating rate auction-rate certificates backed by Government guaranteed student loans | Valuation, Market Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.960	0.950