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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Increase (Decrease) in Members' Capital
Balance			$ 673,912	$ 634,307
Components of comprehensive margin:
Net margin	20,104	23,743	66,630	48,141
Unrealized (loss) gain on available-for-sale securities	205	42	(1,097)	870
Balance	739,445	683,318	739,445	683,318
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Balance			673,009	633,689
Components of comprehensive margin:
Net margin			66,630	48,141
Balance	739,639	681,830	739,639	681,830
Accumulated Other Comprehensive Margin (Deficit)
Increase (Decrease) in Members' Capital
Balance			903	618
Components of comprehensive margin:
Unrealized (loss) gain on available-for-sale securities			(1,097)	870
Balance	$ (194)	$ 1,488	$ (194)	$ 1,488