Fair Value Disclosures - Quantitative Information (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Sep. 30, 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	$ 4,904,657	$ 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	32,824	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	2,003,816	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	$ 17,582	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		$ 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	0.00%	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	89.30%	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	0.00%	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	1.40%	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	1.80%	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	89.30%	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	0.00%	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	2.60%	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	4.30%	3.90%
Fair Value Inputs, Prepayment Rate	23.00%	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	22.00%	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	89.90%	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	0.00%	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	1.80%	1.80%
Fair Value Inputs, Prepayment Rate	12.00%	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	3.00%	3.10%
Fair Value Inputs, Prepayment Rate	10.00%	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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- 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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