Loans and Allowance for Losses and Concentrations of Credit Risk Impaired Financing Receivables (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 113,868		$ 95,869
Impaired Financing Receivable, Recorded Investment	127,383			100,351
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	50,563			30,638
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	50,028			30,236
Impaired Financing Receivable, with Related Allowance, Recorded Investment	76,820			69,713
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	75,093			68,601
Impaired Financing Receivable, Unpaid Principal Balance	125,121			98,837
Impaired Financing Receivable, Related Allowance	3,461			6,659
Financing Receivable, Recorded Investment, Nonaccrual Status	36,686	[1]		45,335	[2]
Impaired Financing Receivable, Interest Income, Accrual Method	1,064		533
Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Average Recorded Investment	31,830		27,676
Impaired Financing Receivable, Recorded Investment	39,151			24,509
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	18,255			7,295
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	18,027			7,247
Impaired Financing Receivable, with Related Allowance, Recorded Investment	20,896			17,214
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	20,209			16,829
Impaired Financing Receivable, Unpaid Principal Balance	38,236			24,076
Impaired Financing Receivable, Related Allowance	737			706
Financing Receivable, Recorded Investment, Nonaccrual Status	10,582	[1]		11,888	[2]
Impaired Financing Receivable, Interest Income, Accrual Method	342		87
Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Average Recorded Investment	46,743		34,003
Impaired Financing Receivable, Recorded Investment	55,266			38,219
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	23,574			11,652
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	23,428			11,509
Impaired Financing Receivable, with Related Allowance, Recorded Investment	31,692			26,567
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	31,023			26,095
Impaired Financing Receivable, Unpaid Principal Balance	54,451			37,604
Impaired Financing Receivable, Related Allowance	1,617			1,515
Financing Receivable, Recorded Investment, Nonaccrual Status	15,358	[1]		15,789	[2]
Impaired Financing Receivable, Interest Income, Accrual Method	374		280
Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Average Recorded Investment	17,906		12,303
Impaired Financing Receivable, Recorded Investment	18,808			17,004
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	6,800			7,644
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	6,659			7,489
Impaired Financing Receivable, with Related Allowance, Recorded Investment	12,008			9,360
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	11,739			9,219
Impaired Financing Receivable, Unpaid Principal Balance	18,398			16,708
Impaired Financing Receivable, Related Allowance	453			355
Financing Receivable, Recorded Investment, Nonaccrual Status	4,024	[1]		5,141	[2]
Impaired Financing Receivable, Interest Income, Accrual Method	154		62
Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Average Recorded Investment	14,197		15,729
Impaired Financing Receivable, Recorded Investment	13,136			15,258
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,934			3,140
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	1,914			3,090
Impaired Financing Receivable, with Related Allowance, Recorded Investment	11,202			12,118
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	11,106			12,007
Impaired Financing Receivable, Unpaid Principal Balance	13,020			15,097
Impaired Financing Receivable, Related Allowance	640			682
Financing Receivable, Recorded Investment, Nonaccrual Status	6,722	[1]		8,180	[2]
Impaired Financing Receivable, Interest Income, Accrual Method	194		104
Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Average Recorded Investment	2,169		5,121
Impaired Financing Receivable, Recorded Investment	0			4,337
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0			0
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0			0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0			4,337
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0			4,337
Impaired Financing Receivable, Unpaid Principal Balance	0			4,337
Impaired Financing Receivable, Related Allowance	0			3,400
Financing Receivable, Recorded Investment, Nonaccrual Status	0	[1]		4,337	[2]
Impaired Financing Receivable, Interest Income, Accrual Method	0		0
Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Average Recorded Investment	1,023		1,037
Impaired Financing Receivable, Recorded Investment	1,022			1,024
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0			907
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0			901
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,022			117
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,016			114
Impaired Financing Receivable, Unpaid Principal Balance	1,016			1,015
Impaired Financing Receivable, Related Allowance	14			1
Financing Receivable, Recorded Investment, Nonaccrual Status	0	[1]		0	[2]
Impaired Financing Receivable, Interest Income, Accrual Method	0		0
Less than 90 days past due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 4,500	[1]		$ 15,700	[1]

[1] Includes $4.5 million of loans that are less than 90 days delinquent but which have not met Farmer Mac's performance criteria for returning to accrual status.

[2] Includes $15.7 million of loans that are less than 90 days delinquent but which have not met Farmer Mac's performance criteria for returning to accrual status.