Consolidated Statements of Patronage Capital and Membership Fees (Unaudited) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Increase (Decrease) in Members' Capital
Net margin	$ 13,145		$ 26,162		$ 39,103	$ 49,366
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Beginning balance	1,098,600	$ 1,072,642	1,039,951	$ 1,016,747	1,072,642	1,016,747
Net margin	13,145	25,958	26,162	23,204
Ending balance	$ 1,111,745	$ 1,098,600	$ 1,066,113	$ 1,039,951	$ 1,111,745	$ 1,066,113