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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Increase (Decrease) in Members' Capital
Balance			$ 713,940	$ 673,912
Components of comprehensive margin:
Net margin	14,453	20,104	50,872	66,630
Unrealized gain (loss) on available-for-sale securities	(118)	205	709	(1,097)
Balance	765,521	739,445	765,521	739,445
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Balance			714,489	673,009
Components of comprehensive margin:
Net margin			50,872	66,630
Balance	765,361	739,639	765,361	739,639
Accumulated Other Comprehensive Margin (Deficit)
Increase (Decrease) in Members' Capital
Balance			(549)	903
Components of comprehensive margin:
Unrealized gain (loss) on available-for-sale securities			709	(1,097)
Balance	$ 160	$ (194)	$ 160	$ (194)