Related Party Transactions Farm Credit Bank of Texas (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
Farm Credit Bank of Texas [Member]
Related Party Transaction [Line Items]
Expense Related to Distribution or Servicing and Underwriting Fees								600,000	800,000	900,000
Common stock, Class B Voting | Farm Credit Bank of Texas [Member]
Related Party Transaction [Line Items]
Common Stock Ownership Percentage by a Related Party	7.70%							7.70%
Long-Term Standby Purchase Commitments [Member] | Farm Credit Bank of Texas [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party										26,400,000
Related Party Transactions, Outstanding Balance	75,100,000				96,700,000			75,100,000	96,700,000
Commitment fees [Member] | Farm Credit Bank of Texas [Member]
Related Party Transaction [Line Items]
Guarantee and commitment fees								$ 300,000	$ 300,000	$ 1,700,000