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, 2017	$ 1,003,020	$ (210)	$ 111,295
Change in Equity
Net margins attributable to the Association	58,870			$ 58,870
Reclassification of unrealized gain on securities available for sale included in net margin		(159)		(159)
Amortization of prior service cost (credit)		(59)		(59)
Net comprehensive income attributable to noncontrolling interest			2,454	2,454
Equity distribution to noncontrolling interest			(4,413)
Equity at end of period at Sep. 30, 2018	1,061,890	(428)	109,336	1,170,798
Equity at beginning of period at Jun. 30, 2018	1,015,492	(408)	110,061
Change in Equity
Net margins attributable to the Association	46,398			46,398
Amortization of prior service cost (credit)		(20)		(20)
Net comprehensive income attributable to noncontrolling interest			830	830
Equity distribution to noncontrolling interest			(1,555)
Equity at end of period at Sep. 30, 2018	1,061,890	(428)	109,336	1,170,798
Equity at beginning of period at Dec. 31, 2018	1,015,754	375	110,169	1,126,298
Change in Equity
Net margins attributable to the Association	60,749			60,749
Amortization of prior service cost (credit)		13		13
Unrecognized prior service cost		(214)		(214)
Net comprehensive income attributable to noncontrolling interest			3,239	3,239
Equity distribution to noncontrolling interest			(2,806)
Equity at end of period at Sep. 30, 2019	1,076,503	174	110,602	1,187,279
Equity at beginning of period at Jun. 30, 2019	1,021,358	184	110,841
Change in Equity
Net margins attributable to the Association	55,145			55,145
Amortization of prior service cost (credit)		(10)		(10)
Net comprehensive income attributable to noncontrolling interest			1,113	1,113
Equity distribution to noncontrolling interest			(1,352)
Equity at end of period at Sep. 30, 2019	$ 1,076,503	$ 174	$ 110,602	$ 1,187,279