Condensed Statements of Patronage Capital and Membership Fees and Accumulated Other Comprehensive Margin (Deficit) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Increase (Decrease) in Members' Capital
Balance			$ 634,307	$ 595,483
Components of comprehensive margin:
Net margin	23,743	10,408	48,141	39,236
Unrealized gain on available-for-sale securities	42	741	870	1,333
Balance	683,318	636,052	683,318	636,052
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Balance			633,689	595,952
Components of comprehensive margin:
Net margin			48,141	39,236
Balance	681,830	635,188	681,830	635,188
Accumulated Other Comprehensive Margin (Deficit)
Increase (Decrease) in Members' Capital
Balance			618	(469)
Components of comprehensive margin:
Unrealized gain on available-for-sale securities			870	1,333
Balance	$ 1,488	$ 864	$ 1,488	$ 864