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

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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.

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

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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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Amount of unrealized holding gain before loss recognized in the income statement for investments in trading securities.

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Fair Value Disclosures - Quantitative Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative Liability		$ 46,769		$ 38,217
Fair Value, Measurements, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative Liability		94,880		84,844
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative Liability		0		0
USDA Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Trading Securities, Unrealized Gains	$ 0	200	$ 700
Institutional Credit [Member] \| Cost Approach Valuation Technique [Member] \| Farmer Mac Guaranteed Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Available-for-sale, at fair value		4,125,962		3,631,662
USDA Guarantees [Member] \| Cost Approach Valuation Technique [Member] \| Farmer Mac Guaranteed Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Available-for-sale, at fair value		30,708		27,619
USDA Guarantees [Member] \| Cost Approach Valuation Technique [Member] \| USDA Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Marketable Securities		1,886,358		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 [Member]
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 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Trading, at fair value		$ 550		$ 689
Floating Interest Rate [Member] \| Cost Approach Valuation Technique [Member] \| Asset-backed Securities [Member] \| Fair Value, Measurements, Recurring [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, Measurements, Recurring [Member] \| 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, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate		16.80%		14.30%
Minimum [Member] \| Institutional Credit [Member] \| Cost Approach Valuation Technique [Member] \| Farmer Mac Guaranteed Securities [Member] \| Fair Value, Measurements, Recurring [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, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate		1.10%		0.80%
Fair Value Inputs, Prepayment Rate		8.00%		0.00%
Minimum [Member] \| USDA Guarantees [Member] \| Cost Approach Valuation Technique [Member] \| USDA Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate		1.20%		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, Measurements, Recurring [Member] \| 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, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate		22.20%		23.90%
Maximum [Member] \| Institutional Credit [Member] \| Cost Approach Valuation Technique [Member] \| Farmer Mac Guaranteed Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate		3.10%		2.70%
Maximum [Member] \| Institutional Credit [Member] \| Cost Approach Valuation Technique [Member] \| USDA Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate		4.10%		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, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate		5.30%		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, Measurements, Recurring [Member] \| 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, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate		19.90%		19.10%
Weighted Average [Member] \| Institutional Credit [Member] \| Cost Approach Valuation Technique [Member] \| Farmer Mac Guaranteed Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate		1.70%		1.30%
Weighted Average [Member] \| Institutional Credit [Member] \| Cost Approach Valuation Technique [Member] \| USDA Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate		1.90%		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, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate		3.20%		3.20%
Fair Value Inputs, Prepayment Rate		8.00%		8.00%