Consolidated Statements of Equity - USD ($) $ in Thousands	Patronage capital	Accumulated other comprehensive income (loss)	Noncontrolling interest	Total
Equity at beginning of period at Dec. 31, 2016	$ 961,364	$ (286)	$ 109,147
Change in Equity
Net margins attributable to the Association	61,656			$ 61,656
Retirement of patronage capital	(20,000)
Unrealized gain on securities available for sale		43
Unrecognized actuarial gain (loss) on postretirement benefit obligation		106		106
Reclassification adjustment for actuarial (gain) loss on postretirement benefit obligation included in net margin		(73)
Amortization of actuarial (gain) loss on postretirement benefit obligation included in net margin				(73)
Net comprehensive income attributable to noncontrolling interest			2,148	2,148
Equity at end of period at Dec. 31, 2017	1,003,020	(210)	111,295	1,114,105
Change in Equity
Net margins attributable to the Association	42,734			42,734
Retirement of patronage capital	(30,000)
Unrecognized actuarial gain (loss) on postretirement benefit obligation		456		456
Reclassification of unrealized gain on securities available for sale included in net margin		(159)		(159)
Reclassification adjustment for actuarial (gain) loss on postretirement benefit obligation included in net margin		288
Amortization of actuarial (gain) loss on postretirement benefit obligation included in net margin				288
Net comprehensive income attributable to noncontrolling interest			3,287	3,287
Equity distribution to noncontrolling interest			(4,413)
Equity at end of period at Dec. 31, 2018	1,015,754	375	110,169	1,126,298
Change in Equity
Net margins attributable to the Association	45,309			45,309
Retirement of patronage capital	(30,000)
Unrecognized actuarial gain (loss) on postretirement benefit obligation		(1,341)		(1,341)
Reclassification adjustment for actuarial (gain) loss on postretirement benefit obligation included in net margin		(338)
Unrecognized prior service cost		(214)		(214)
Amortization of actuarial (gain) loss on postretirement benefit obligation included in net margin				(338)
Net comprehensive income attributable to noncontrolling interest			4,354	4,354
Equity distribution to noncontrolling interest			(2,806)
Equity at end of period at Dec. 31, 2019	$ 1,031,063	$ (1,518)	$ 111,717	$ 1,141,262