Fair Value Disclosures - Quantitative Information (Details) - Fair Value, Measurements, Recurring [Member] - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017		Dec. 31, 2016		Mar. 31, 2016	Dec. 31, 2015
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 5,284,591		$ 4,891,803		$ 6,518,500	$ 6,115,339
USDA Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 18,602		$ 20,388		1,934,883	1,917,319
Minimum [Member] | Floating rate auction-rate certificates backed by Government guaranteed student loans | Market Approach Valuation Technique [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Range of Offered Quotes	92.00%		90.00%
Minimum [Member] | Institutional Credit [Member] | Farmer Mac Guaranteed Securities [Member] | Cost Approach Valuation Technique [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	1.70%		1.50%
Minimum [Member] | Institutional Credit [Member] | USDA Securities [Member] | Cost Approach Valuation Technique [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate
Fair Value Inputs, Prepayment Rate
Minimum [Member] | USDA Guarantees [Member] | USDA Securities [Member] | Cost Approach Valuation Technique [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	3.70%		4.00%
Fair Value Inputs, Prepayment Rate	9.00%		13.00%
Maximum [Member] | Floating rate auction-rate certificates backed by Government guaranteed student loans | Market Approach Valuation Technique [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Range of Offered Quotes	92.00%		90.00%
Maximum [Member] | Institutional Credit [Member] | Farmer Mac Guaranteed Securities [Member] | Cost Approach Valuation Technique [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	3.30%		3.30%
Maximum [Member] | Institutional Credit [Member] | USDA Securities [Member] | Cost Approach Valuation Technique [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate
Fair Value Inputs, Prepayment Rate
Maximum [Member] | USDA Guarantees [Member] | USDA Securities [Member] | Cost Approach Valuation Technique [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%		18.00%
Weighted Average [Member] | Floating rate auction-rate certificates backed by Government guaranteed student loans | Market Approach Valuation Technique [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Range of Offered Quotes	92.00%		90.00%
Weighted Average [Member] | Institutional Credit [Member] | Farmer Mac Guaranteed Securities [Member] | Cost Approach Valuation Technique [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	2.00%		1.90%
Weighted Average [Member] | Institutional Credit [Member] | USDA Securities [Member] | Cost Approach Valuation Technique [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate
Fair Value Inputs, Prepayment Rate
Weighted Average [Member] | USDA Guarantees [Member] | USDA Securities [Member] | Cost Approach Valuation Technique [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	5.00%		5.00%
Fair Value Inputs, Prepayment Rate	17.00%		17.00%
Available-for-sale Securities [Member] | Farmer Mac Guaranteed Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 5,243,046		$ 4,853,685		4,565,504	4,152,605
Available-for-sale Securities [Member] | USDA Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	0		0		1,908,014	1,888,344
Available-for-sale Securities [Member] | Institutional Credit [Member] | Farmer Mac Guaranteed Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	5,243,046	[1]	4,853,685	[1]	4,534,810	4,121,244
Available-for-sale Securities [Member] | USDA Guarantees [Member] | Farmer Mac Guaranteed Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value					30,694	31,361
Available-for-sale Securities [Member] | Fixed Interest Rate [Member] | Government/GSE Guaranteed Mortgage Backed Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 4,819		$ 0
Fair Value Inputs, Prepayment Rate	0.00%		0.00%
Available-for-sale Securities [Member] | Minimum [Member] | Fixed Interest Rate [Member] | Government/GSE Guaranteed Mortgage Backed Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	3.40%		0.00%
Available-for-sale Securities [Member] | Maximum [Member] | Fixed Interest Rate [Member] | Government/GSE Guaranteed Mortgage Backed Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	3.40%		0.00%
Available-for-sale Securities [Member] | Weighted Average [Member] | Fixed Interest Rate [Member] | Government/GSE Guaranteed Mortgage Backed Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs, Discount Rate	3.40%		0.00%
Trading Securities [Member] | USDA Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 18,602	[1]	$ 20,388	[1]	$ 26,869	$ 28,975

[1] Includes unrealized losses of $44,000 attributable to assets still held as of March 31, 2017 that are recorded in "(Losses)/gains on trading securities."