Consolidated Statements of Patronage Capital and Membership Fees and Accumulated Other Comprehensive Margin (Deficit) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Increase (Decrease) in Members' Capital
Balance			$ 911,087	$ 859,440
Components of comprehensive margin:
Net margin	$ 11,334	$ 11,555	56,019	48,685
Unrealized loss on available-for-sale securities		56		18
Balance	967,106	908,143	967,106	908,143
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Balance			911,087	859,810
Components of comprehensive margin:
Net margin			56,019	48,685
Balance	$ 967,106	908,495	$ 967,106	908,495
Accumulated Other Comprehensive Deficit
Increase (Decrease) in Members' Capital
Balance				(370)
Components of comprehensive margin:
Unrealized loss on available-for-sale securities				18
Balance		$ (352)		$ (352)