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, 2018	$ 1,015,754	$ 375	$ 110,169
Change in Equity
Net margins attributable to the Association	6,989			$ 6,989
Amortization of prior period cost				33
Reclassification adjustment for actuarial (gain) loss on postretirement benefit obligation included in net margin		33
Unrecognized prior service cost		(214)		(214)
Net comprehensive income attributable to noncontrolling interest			1,017	1,017
Equity distribution to noncontrolling interest			(1,454)
Equity at end of period at Mar. 31, 2019	1,022,743	194	109,732	1,132,669
Equity at beginning of period at Dec. 31, 2019	1,031,063	(1,518)	111,717	1,141,262
Change in Equity
Net margins attributable to the Association	(4,610)			(4,610)
Amortization of prior period cost				933
Reclassification adjustment for actuarial (gain) loss on postretirement benefit obligation included in net margin		933
Unrecognized prior service cost		(7,373)		(7,373)
Net comprehensive income attributable to noncontrolling interest			1,319	1,319
Equity distribution to noncontrolling interest			(1,268)
Equity at end of period at Mar. 31, 2020	$ 1,026,453	$ (7,958)	$ 111,768	$ 1,130,263