Consolidated Statements of Patronage Capital and Membership Fees and Accumulated Other Comprehensive Margin - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Increase (Decrease) in Members' Capital
Balance			$ 809,523	$ 761,592
Components of comprehensive margin:
Net margin	$ 18,630	$ 15,908	62,505	42,129
Unrealized (loss) gain on available-for-sale securities	(19)	(95)	358	(267)
Balance	872,386	803,454	872,386	803,454
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Balance			809,465	761,124
Components of comprehensive margin:
Net margin			62,505	42,129
Balance	871,970	803,253	871,970	803,253
Accumulated Other Comprehensive Margin
Increase (Decrease) in Members' Capital
Balance			58	468
Components of comprehensive margin:
Unrealized (loss) gain on available-for-sale securities			358	(267)
Balance	$ 416	$ 201	$ 416	$ 201