Related Party Transactions CFC (National Rural Utilities Cooperative Financial Corporation) (Details) (USD $)	3 Months Ended							12 Months Ended			15 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2012
Related Party Transaction [Line Items]
Common Stock Ownership Percentage by a Related Party	5.00%							5.00%
Guarantee and commitment fees	$ 6,568,000	$ 6,401,000	$ 6,064,000	$ 5,930,000	$ 5,966,000	$ 6,320,000	$ 6,387,000	$ 24,963,000	$ 24,821,000	$ 24,091,000	$ 6,148,000
Interest receivable	103,414,000				110,339,000			103,414,000	110,339,000
Total interest income	56,151,000	63,810,000	71,578,000	73,131,000	72,642,000	66,852,000	64,072,000	264,670,000	274,687,000	238,711,000	71,121,000
AgFirst Farm Credit Bank [Member]
Related Party Transaction [Line Items]
Guarantee and commitment fees								500,000	400,000	400,000
CFC [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Related Party's percent of total Program								100.00%	100.00%	100.00%
Related Party's percent of Farmer Mac Total Outstanding Book of Business	18.00%				19.70%			18.00%	19.70%
Accrued Fees and Other Revenue Receivable	700,000				1,100,000			700,000	1,100,000	1,200,000
Guarantee and commitment fees								4,400,000	5,400,000	6,000,000
Interest receivable	5,700,000				8,200,000			5,700,000	8,200,000
Total interest income								28,000,000	30,900,000	32,700,000
Rural Utilities [Member] | CFC [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party								549,523,000	206,585,000	965,952,000
Rural Utilities [Member] | Mortgage Loans on Real Estate [Member] | CFC [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party								166,117,000	203,789,000	313,028,000
On-balance sheet [Member] | Rural Utilities [Member] | Farmer Mac Guaranteed Securities [Member] | CFC [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party								383,406,000	0	650,000,000
Off-balance sheet [Member] | Rural Utilities [Member] | Farmer Mac Guaranteed Securities [Member] | CFC [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party								$ 0	$ 2,796,000	$ 2,924,000
Common Class A [Member] | CFC [Member]
Related Party Transaction [Line Items]
Common Stock Ownership Percentage by a Related Party	7.90%							7.90%
Rural Utilities [Member] | CFC [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Related Party's percent of total purchases								18.60%	6.10%	32.50%