Consolidated Statements of Patronage Capital and Membership Fees (Unaudited) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Increase (Decrease) in Members' Capital
Net margin	$ 8,471			$ 18,286			$ 57,837	$ 51,265
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Beginning balance	1,066,113	$ 1,039,951	$ 1,016,747	995,265	$ 985,882	$ 962,286	1,016,747	962,286
Net margin	8,471	26,162	23,204	18,286	9,383	23,596
Ending balance	$ 1,074,584	$ 1,066,113	$ 1,039,951	$ 1,013,551	$ 995,265	$ 985,882	$ 1,074,584	$ 1,013,551