Fair Value Disclosures - Quantitative Information (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Institutional Credit [Member] \| Cost Approach Valuation Technique [Member] \| Farmer Mac Guaranteed Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Available-for-sale, at fair value	$ 4,121,244	$ 3,631,662
USDA Guarantees [Member] \| Cost Approach Valuation Technique [Member] \| Farmer Mac Guaranteed Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Available-for-sale, at fair value	31,361	27,619
USDA Guarantees [Member] \| Cost Approach Valuation Technique [Member] \| USDA Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Marketable Securities	1,917,319	1,771,532
Floating Interest Rate [Member] \| Market Approach Valuation Technique [Member] \| Floating rate auction-rate certificates backed by Government guaranteed student loans
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Available-for-sale, at fair value	44,924	40,576
Floating Interest Rate [Member] \| Cost Approach Valuation Technique [Member] \| Asset-backed Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Trading, at fair value	$ 491	$ 689
Floating Interest Rate [Member] \| Cost Approach Valuation Technique [Member] \| Asset-backed Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Prepayment Rate	10.00%	10.00%
Minimum [Member] \| Market Approach Valuation Technique [Member] \| Floating rate auction-rate certificates backed by Government guaranteed student loans \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Range of Offered Quotes	92.00%	82.00%
Minimum [Member] \| Cost Approach Valuation Technique [Member] \| Asset-backed Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	18.30%	14.30%
Minimum [Member] \| Institutional Credit [Member] \| Cost Approach Valuation Technique [Member] \| Farmer Mac Guaranteed Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	1.10%	0.70%
Minimum [Member] \| Institutional Credit [Member] \| Cost Approach Valuation Technique [Member] \| USDA Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	1.00%	0.80%
Fair Value Inputs, Prepayment Rate	9.00%	0.00%
Minimum [Member] \| USDA Guarantees [Member] \| Cost Approach Valuation Technique [Member] \| USDA Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	1.30%	1.10%
Fair Value Inputs, Prepayment Rate	0.00%	0.00%
Maximum [Member] \| Market Approach Valuation Technique [Member] \| Floating rate auction-rate certificates backed by Government guaranteed student loans \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Range of Offered Quotes	99.60%	94.00%
Maximum [Member] \| Cost Approach Valuation Technique [Member] \| Asset-backed Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	23.90%	23.90%
Maximum [Member] \| Institutional Credit [Member] \| Cost Approach Valuation Technique [Member] \| Farmer Mac Guaranteed Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	3.30%	2.70%
Maximum [Member] \| Institutional Credit [Member] \| Cost Approach Valuation Technique [Member] \| USDA Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	3.90%	3.60%
Fair Value Inputs, Prepayment Rate	20.00%	21.00%
Maximum [Member] \| USDA Guarantees [Member] \| Cost Approach Valuation Technique [Member] \| USDA Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	5.10%	5.30%
Fair Value Inputs, Prepayment Rate	19.00%	20.00%
Weighted Average [Member] \| Market Approach Valuation Technique [Member] \| Floating rate auction-rate certificates backed by Government guaranteed student loans \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Range of Offered Quotes	96.60%	87.10%
Weighted Average [Member] \| Cost Approach Valuation Technique [Member] \| Asset-backed Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	21.50%	19.10%
Weighted Average [Member] \| Institutional Credit [Member] \| Cost Approach Valuation Technique [Member] \| Farmer Mac Guaranteed Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	1.80%	1.30%
Weighted Average [Member] \| Institutional Credit [Member] \| Cost Approach Valuation Technique [Member] \| USDA Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	1.80%	1.90%
Fair Value Inputs, Prepayment Rate	10.00%	9.00%
Weighted Average [Member] \| USDA Guarantees [Member] \| Cost Approach Valuation Technique [Member] \| USDA Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	3.10%	3.20%
Fair Value Inputs, Prepayment Rate	7.00%	8.00%

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- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

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-Publisher FASB
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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.

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- Definition

Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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