Consolidated Statements of Equity (Unaudited) - USD ($) $ in Thousands	Total	Postretirement Medical Benefit Plans	Executive Benefit Restoration Plan	Patronage capital	Accumulated other comprehensive income (loss)	Accumulated other comprehensive income (loss) Postretirement Medical Benefit Plans	Accumulated other comprehensive income (loss) Executive Benefit Restoration Plan	Noncontrolling interest
Equity at beginning of period at Dec. 31, 2022				$ 984,865	$ (468)			$ 126,180
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net margins attributable to the Association	$ (8,161)			(8,161)
Retirement of patronage capital				0
Unrealized gain on securities available for sale	26				26
Amortization of prior service credit into other income		$ (1,228)	$ 867			$ (1,228)	$ 867
Net comprehensive income attributable to noncontrolling interest	(7,444)							7,444
Equity distribution to noncontrolling interest								(1,882)
Equity at end of period at Sep. 30, 2023	1,107,643			976,704	(803)			131,742
Equity at beginning of period at Jun. 30, 2023				930,223	(693)			130,149
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net margins attributable to the Association	46,481			46,481
Retirement of patronage capital				0
Unrealized gain on securities available for sale	10				10
Amortization of prior service credit into other income		(409)	289			(409)	289
Net comprehensive income attributable to noncontrolling interest	(2,526)							2,526
Equity distribution to noncontrolling interest								(933)
Equity at end of period at Sep. 30, 2023	1,107,643			976,704	(803)			131,742
Equity at beginning of period at Dec. 31, 2023	1,118,011			984,581	(839)			134,269
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net margins attributable to the Association	40,273			40,273
Retirement of patronage capital				(82,200)
Unrealized gain on securities available for sale	175				175
Amortization of prior service credit into other income		(661)	729			(661)	729
Net comprehensive income attributable to noncontrolling interest	(6,457)							6,457
Equity distribution to noncontrolling interest								(10,273)
Equity at end of period at Sep. 30, 2024	1,072,511			942,654	(596)			130,453
Equity at beginning of period at Jun. 30, 2024				887,861	(801)			129,738
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net margins attributable to the Association	54,793			54,793
Retirement of patronage capital				0
Unrealized gain on securities available for sale	110				110
Amortization of prior service credit into other income		$ (125)	$ 220			$ (125)	$ 220
Net comprehensive income attributable to noncontrolling interest	(960)							960
Equity distribution to noncontrolling interest								(245)
Equity at end of period at Sep. 30, 2024	$ 1,072,511			$ 942,654	$ (596)			$ 130,453