Fair Value Disclosures - Quantitative Information (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2016	Dec. 31, 2015
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	$ 4,534,810	$ 4,121,244
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	30,694	31,361
USDA Guarantees [Member] \| Cost Approach Valuation Technique [Member] \| USDA Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Marketable Securities	1,934,883	1,917,319
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	17,730	44,924
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	$ 383	$ 491
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	90.00%	92.00%
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	22.50%	18.30%
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	1.30%	1.10%
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	1.30%	1.00%
Fair Value Inputs, Prepayment Rate	9.00%	9.00%
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	1.60%	1.30%
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	90.00%	99.60%
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	26.50%	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	2.80%	3.30%
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	4.20%	3.90%
Fair Value Inputs, Prepayment Rate	22.00%	20.00%
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%	5.10%
Fair Value Inputs, Prepayment Rate	21.00%	19.00%
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	90.00%	96.60%
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	24.90%	21.50%
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	1.70%	1.80%
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	2.00%	1.80%
Fair Value Inputs, Prepayment Rate	11.00%	10.00%
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%	3.10%
Fair Value Inputs, Prepayment Rate	9.00%	7.00%

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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

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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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