Consolidated Statements of Patronage Capital and Membership Fees and Accumulated Other Comprehensive Margin - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Increase (Decrease) in Members' Capital
Balance			$ 809,523	$ 761,592
Components of comprehensive margin:
Net margin	$ 23,277	$ 10,852	43,875	26,221
Unrealized gain (loss) on available-for-sale securities	93	(314)	377	(361)
Balance	853,775	787,452	853,775	787,452
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Balance			809,465	761,124
Components of comprehensive margin:
Net margin			43,875	26,221
Balance	853,340	787,345	853,340	787,345
Accumulated Other Comprehensive Margin
Increase (Decrease) in Members' Capital
Balance			58	468
Components of comprehensive margin:
Unrealized gain (loss) on available-for-sale securities			377	(361)
Balance	$ 435	$ 107	$ 435	$ 107