Consolidated Statements of Patronage Capital and Membership Fees and Accumulated Other Comprehensive Margin - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Increase (Decrease) in Members' Capital
Balance	$ 809,523	$ 761,592
Components of comprehensive margin:
Net margin	20,598	15,369
Unrealized gain (loss) on available-for-sale securities	284	(47)
Balance	830,405	776,914
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Balance	809,465	761,124
Components of comprehensive margin:
Net margin	20,598	15,369
Balance	830,063	776,493
Accumulated Other Comprehensive Margin
Increase (Decrease) in Members' Capital
Balance	58	468
Components of comprehensive margin:
Unrealized gain (loss) on available-for-sale securities	284	(47)
Balance	$ 342	$ 421