Fair Value Disclosures - Quantitative Information (Details) (USD $) In Thousands, unless otherwise specified																				3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended		12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended		12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended		12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended									3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended			3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Indicative Bid Approach Valuation Technique [Member] Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Indicative Bid Approach Valuation Technique [Member] Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Asset-backed Securities [Member] Floating Interest Rate [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Asset-backed Securities [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Collateralized Mortgage Backed Securities [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Farmer Mac Guarantee	Mar. 31, 2012 Farmer Mac Guarantee	Mar. 31, 2013 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Farm & Ranch Guaranteed Securities [Member]	Dec. 31, 2012 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Farm & Ranch Guaranteed Securities [Member]	Mar. 31, 2013 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique	Dec. 31, 2012 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique	Mar. 31, 2013 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guaranteed Securities - Rural Utilities	Dec. 31, 2012 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guaranteed Securities - Rural Utilities	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Indicative Bid Approach Valuation Technique [Member] Minimum [Member] Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member] Indicative Bid Approach Valuation Technique [Member] Minimum [Member] Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Indicative Bid Approach Valuation Technique [Member] Maximum [Member] Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member] Indicative Bid Approach Valuation Technique [Member] Maximum [Member] Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Indicative Bid Approach Valuation Technique [Member] Weighted Average Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member] Indicative Bid Approach Valuation Technique [Member] Weighted Average Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Asset-backed Securities [Member] Floating Interest Rate [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Asset-backed Securities [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Collateralized Mortgage Obligations [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Minimum [Member] Derivative Financial Instruments, Liabilities [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Minimum [Member] Derivative Financial Instruments, Liabilities [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Minimum [Member] Asset-backed Securities [Member] Floating Interest Rate [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Minimum [Member] Asset-backed Securities [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Minimum [Member] Collateralized Mortgage Obligations [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Maximum [Member] Derivative Financial Instruments, Liabilities [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Maximum [Member] Derivative Financial Instruments, Liabilities [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Maximum [Member] Asset-backed Securities [Member] Floating Interest Rate [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Maximum [Member] Asset-backed Securities [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Maximum [Member] Collateralized Mortgage Obligations [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Weighted Average Derivative Financial Instruments, Liabilities [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Weighted Average Derivative Financial Instruments, Liabilities [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Weighted Average Asset-backed Securities [Member] Floating Interest Rate [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Weighted Average Asset-backed Securities [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Weighted Average Collateralized Mortgage Obligations [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Farmer Mac Guaranteed Securities [Member]	Dec. 31, 2012 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Farmer Mac Guaranteed Securities [Member]	Mar. 31, 2013 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Farm & Ranch Guaranteed Securities [Member]	Dec. 31, 2012 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Farm & Ranch Guaranteed Securities [Member]	Mar. 31, 2013 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member]	Mar. 31, 2013 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Farmer Mac Guaranteed Securities - Rural Utilities	Dec. 31, 2012 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Farmer Mac Guaranteed Securities - Rural Utilities	Mar. 31, 2013 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Minimum [Member] Farm & Ranch Guaranteed Securities [Member]	Dec. 31, 2012 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Minimum [Member] Farm & Ranch Guaranteed Securities [Member]	Mar. 31, 2013 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Minimum [Member]	Dec. 31, 2012 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Minimum [Member]	Mar. 31, 2013 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Minimum [Member] Farmer Mac Guaranteed Securities - Rural Utilities	Dec. 31, 2012 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Minimum [Member] Farmer Mac Guaranteed Securities - Rural Utilities	Mar. 31, 2013 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Maximum [Member] Farm & Ranch Guaranteed Securities [Member]	Dec. 31, 2012 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Maximum [Member] Farm & Ranch Guaranteed Securities [Member]	Mar. 31, 2013 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Maximum [Member]	Dec. 31, 2012 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Maximum [Member]	Mar. 31, 2013 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Maximum [Member] Farmer Mac Guaranteed Securities - Rural Utilities	Dec. 31, 2012 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Maximum [Member] Farmer Mac Guaranteed Securities - Rural Utilities	Mar. 31, 2013 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Weighted Average Farm & Ranch Guaranteed Securities [Member]	Dec. 31, 2012 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Weighted Average Farm & Ranch Guaranteed Securities [Member]	Mar. 31, 2013 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Weighted Average	Dec. 31, 2012 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Weighted Average	Mar. 31, 2013 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Weighted Average Farmer Mac Guaranteed Securities - Rural Utilities	Dec. 31, 2012 Level 3 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Weighted Average Farmer Mac Guaranteed Securities - Rural Utilities	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Minimum [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Minimum [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Maximum [Member]	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Maximum [Member]	Mar. 31, 2013 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Weighted Average	Dec. 31, 2012 Level 3 Fair Value, Measurements, Recurring [Member] Discounted Cash Flows Approach Valuation Technique Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Available-for-sale securities	$ 65,213	$ 63,159					$ 233	$ 5,100,080	$ 4,766,258	$ 3,528,520	$ 3,426,489	$ 27,198	$ 26,681	$ 1,544,362	$ 1,313,088			$ 65,446	$ 63,159																									$ 5,100,080	$ 4,766,258	$ 3,528,520	$ 3,426,489	$ 27,198	$ 26,681	$ 1,544,362	$ 1,313,088																			$ 1,569,160	$ 1,486,595
Trading securities					1,129	1,247												1,129	1,247																																																			87,271	104,188
Marketable Securities																1,656,431	1,590,783	66,575	64,406																																																			1,656,431	1,590,783
Financial derivatives, Liabilities			$ 532	$ 691														$ 532	$ 691
Fair Value Inputs, Range of Offered Quotes																				82.00%	82.00%	93.00%	90.00%	88.00%	85.00%
Fair Value Inputs, discount rate																													0.60%	1.00%	11.90%	12.40%	1.60%	2.40%	3.00%	19.40%	19.70%	1.60%	1.30%	1.70%	15.90%	16.20%	1.60%									0.90%	1.10%	0.80%	1.00%	0.80%	0.80%	3.50%	3.40%	3.30%	3.40%	3.00%	2.90%	1.60%	1.60%	1.90%	2.10%	1.60%	1.60%			1.20%	1.40%	5.30%	5.30%	3.10%	3.40%
Fair Value Inputs, Constant Prepayment Rate																										10.00%	10.00%	7.00%	12.00%	11.00%				17.00%	19.00%				16.00%	16.00%														8.00%	8.00%					18.00%	17.00%					15.00%	14.00%					0.00%	0.00%	27.00%	26.00%	9.00%	10.00%