Related Party Transactions Farm Credit West (Details) (USD $)	3 Months Ended							12 Months Ended			15 Months Ended	12 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	Dec. 31, 2012 Farm Credit West [Member]	Dec. 31, 2011 Farm Credit West [Member]	Dec. 31, 2010 Farm Credit West [Member]	Dec. 31, 2012 AgFirst Farm Credit Bank [Member]	Dec. 31, 2011 AgFirst Farm Credit Bank [Member]	Dec. 31, 2010 AgFirst Farm Credit Bank [Member]	Dec. 31, 2012 Long-Term Standby Purchase Commitments [Member] Farm Credit West [Member]	Dec. 31, 2011 Long-Term Standby Purchase Commitments [Member] Farm Credit West [Member]	Dec. 31, 2010 Long-Term Standby Purchase Commitments [Member] Farm Credit West [Member]	Dec. 31, 2012 Long-Term Standby Purchase Commitments [Member] AgFirst Farm Credit Bank [Member]	Dec. 31, 2011 Long-Term Standby Purchase Commitments [Member] AgFirst Farm Credit Bank [Member]	Dec. 31, 2010 Long-Term Standby Purchase Commitments [Member] AgFirst Farm Credit Bank [Member]	Dec. 31, 2012 Commitment fees [Member] Farm Credit West [Member]	Dec. 31, 2012 Commitment fees [Member] AgFirst Farm Credit Bank [Member]	Dec. 31, 2011 Commitment fees [Member] AgFirst Farm Credit Bank [Member]	Dec. 31, 2010 Commitment fees [Member] AgFirst Farm Credit Bank [Member]	Dec. 31, 2006 Conversion of Long-Term Standby Purchase Commitments to Farmer Mac Guaranteed Securirites [Member] Farm Credit West [Member]	Dec. 31, 2003 Conversion of Long-Term Standby Purchase Commitments to Farmer Mac Guaranteed Securirites [Member] Farm Credit West [Member]	Dec. 31, 2012 Conversion of Long-Term Standby Purchase Commitments to Farmer Mac Guaranteed Securirites [Member] Farm Credit West [Member]	Dec. 31, 2011 Conversion of Long-Term Standby Purchase Commitments to Farmer Mac Guaranteed Securirites [Member] Farm Credit West [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party																		$ 8,100,000	$ 2,100,000	$ 500,000	$ 16,800,000	$ 8,600,000	$ 116,200,000					$ 129,000,000	$ 722,300,000
Related Party Transactions, Outstanding Balance																		95,400,000	98,300,000		186,500,000	225,000,000	387,900,000		100,000	100,000				420,900,000	498,100,000
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	1,900,000	2,300,000	2,600,000	500,000	400,000	400,000							300,000	800,000	1,000,000	1,500,000
Expense Related to Distribution or Servicing and Underwriting Fees												$ 900,000	$ 1,000,000	$ 1,900,000