Consolidated Statements of Patronage Capital and Membership Fees and Accumulated Other Comprehensive (Deficit) Margin - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Increase (Decrease) in Members' Capital
Balance			$ 859,440	$ 809,523
Components of comprehensive margin:
Net margin	$ 20,805	$ 18,630	63,685	62,505
Unrealized gain on available-for-sale securities	56	(19)	18	358
Balance	923,143	872,386	923,143	872,386
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Balance			859,810	809,465
Components of comprehensive margin:
Net margin			63,685	62,505
Balance	923,495	871,970	923,495	871,970
Accumulated Other Comprehensive (Deficit) Margin
Increase (Decrease) in Members' Capital
Balance			(370)	58
Components of comprehensive margin:
Unrealized gain on available-for-sale securities			18	358
Balance	$ (352)	$ 416	$ (352)	$ 416