Related Party Transactions AgStar Financial Services (Details) (USD $)	3 Months Ended							12 Months Ended			15 Months Ended	12 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, 2010 AgStar Financial Services, ACA [Member]	Dec. 31, 2009 AgStar Financial Services, ACA [Member]	Dec. 31, 2010 Commitment fees [Member] AgStar Financial Services, ACA [Member]	Dec. 31, 2010 Farmer Mac Guaranteed Securities [Member] Sale of Farmer Mac Guaranteed Securities [Member] AgStar Financial Services, ACA [Member]	Dec. 31, 2010 Defaulted Loans pursuant to LTSPC agreement [Member] AgStar Financial Services, ACA [Member]	Dec. 31, 2010 Long-Term Standby Purchase Commitments [Member] AgStar Financial Services, ACA [Member]
Related Party Transaction [Line Items]
Servicing Fees, Net												$ 1,400,000
Related Party Transaction, Purchases from Related Party																100,000	30,300,000
Related Party Transaction, Amounts of Transaction															2,900,000
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	1,700,000		1,100,000
Related Party Transactions, Outstanding Balance													$ 449,200,000