Fair Value Disclosures - Quantitative Information (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative Liability	$ 34,038	$ 38,217
Fair Value, Measurements, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative Liability	69,373	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
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	4,016,200	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	35,008	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	1,859,176	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	40,182	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	$ 606	$ 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	82.00%	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	15.50%	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	0.80%	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	1.00%	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	1.10%	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	94.00%	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	21.70%	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	3.30%	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	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, 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	18.00%	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	86.20%	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	18.90%	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	1.50%	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	11.00%	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	3.10%	3.20%
Fair Value Inputs, Prepayment Rate	7.00%	8.00%