Consolidated Statements of Patronage Capital and Membership Fees (Unaudited) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Increase (Decrease) in Members' Capital
Net margin	$ 8,907			$ 8,471			$ 48,010	$ 57,837
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Beginning balance	1,111,745	$ 1,098,600	$ 1,072,642	1,066,113	$ 1,039,951	$ 1,016,747	1,072,642	1,016,747
Net margin	8,907	13,145	25,958	8,471	26,162	23,204
Ending balance	$ 1,120,652	$ 1,111,745	$ 1,098,600	$ 1,074,584	$ 1,066,113	$ 1,039,951	$ 1,120,652	$ 1,074,584