Fair Value Disclosures - Quantitative Information (Details) - Fair Value, Measurements, Recurring [Member] - Fair Value, Inputs, Level 3 [Member] $ in Thousands	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 6,003,211	$ 5,508,576	$ 4,891,803	$ 6,115,339
USDA Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	9,999	13,515	20,388	1,917,319
Available-for-sale Securities [Member] | Farmer Mac Guaranteed Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	5,974,497	5,471,914	4,853,685	4,152,605
Available-for-sale Securities [Member] | USDA Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	0	0	0	1,888,344
Available-for-sale Securities [Member] | Institutional Credit [Member] | Farmer Mac Guaranteed Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	5,974,497	5,471,914	4,853,685	4,121,244
Available-for-sale Securities [Member] | USDA Guarantees [Member] | Farmer Mac Guaranteed Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			0	31,361
Available-for-sale Securities [Member] | Fixed Interest Rate [Member] | Government/GSE Guaranteed Mortgage Backed Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	0	4,333	0
Trading Securities [Member] | USDA Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 9,999	$ 13,515	$ 20,388	$ 28,975
Measurement Input, Range of Broker Quotes [Member] | Minimum [Member] | Floating rate auction-rate certificates backed by Government guaranteed student loans | Valuation, Market Approach [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.963	0.955
Measurement Input, Range of Broker Quotes [Member] | Maximum [Member] | Floating rate auction-rate certificates backed by Government guaranteed student loans | Valuation, Market Approach [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.963	0.955
Measurement Input, Range of Broker Quotes [Member] | Weighted Average [Member] | Floating rate auction-rate certificates backed by Government guaranteed student loans | Valuation, Market Approach [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.963	0.955
Measurement Input, Discount Rate [Member] | Minimum [Member] | Institutional Credit [Member] | Farmer Mac Guaranteed Securities [Member] | Valuation, Cost Approach [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.029	0.021
Measurement Input, Discount Rate [Member] | Minimum [Member] | USDA Guarantees [Member] | USDA Securities [Member] | Valuation, Cost Approach [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.033	0.036
Measurement Input, Discount Rate [Member] | Maximum [Member] | Institutional Credit [Member] | Farmer Mac Guaranteed Securities [Member] | Valuation, Cost Approach [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.040	0.034
Measurement Input, Discount Rate [Member] | Maximum [Member] | USDA Guarantees [Member] | USDA Securities [Member] | Valuation, Cost Approach [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.052	0.054
Measurement Input, Discount Rate [Member] | Weighted Average [Member] | Institutional Credit [Member] | Farmer Mac Guaranteed Securities [Member] | Valuation, Cost Approach [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.031	0.024
Measurement Input, Discount Rate [Member] | Weighted Average [Member] | USDA Guarantees [Member] | USDA Securities [Member] | Valuation, Cost Approach [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.049	0.050
Measurement Input, Discount Rate [Member] | Available-for-sale Securities [Member] | Minimum [Member] | Fixed Interest Rate [Member] | Government/GSE Guaranteed Mortgage Backed Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.000	0.029
Measurement Input, Discount Rate [Member] | Available-for-sale Securities [Member] | Maximum [Member] | Fixed Interest Rate [Member] | Government/GSE Guaranteed Mortgage Backed Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.000	0.029
Measurement Input, Discount Rate [Member] | Available-for-sale Securities [Member] | Weighted Average [Member] | Fixed Interest Rate [Member] | Government/GSE Guaranteed Mortgage Backed Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.000	0.029
Measurement Input, Constant Prepayment Rate [Member] | Minimum [Member] | USDA Guarantees [Member] | USDA Securities [Member] | Valuation, Cost Approach [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.06	0.07
Measurement Input, Constant Prepayment Rate [Member] | Maximum [Member] | USDA Guarantees [Member] | USDA Securities [Member] | Valuation, Cost Approach [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.16	0.19
Measurement Input, Constant Prepayment Rate [Member] | Weighted Average [Member] | USDA Guarantees [Member] | USDA Securities [Member] | Valuation, Cost Approach [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USDA securities, measurement input	0.15	0.17
Measurement Input, Constant Prepayment Rate [Member] | Available-for-sale Securities [Member] | Fixed Interest Rate [Member] | Government/GSE Guaranteed Mortgage Backed Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities, measurement input	0.00	0.00