Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Consolidated Statements of Comprehensive Income
Net margins including noncontrolling interest	$ 63,804	$ 32,197	$ 52,924
Other comprehensive income (loss):
Unrealized gain (loss) on securities available for sale	43	(13)	(125)
Unrecognized actuarial gain (loss) on postretirement benefit obligation	106	(821)	1,528
Amortization of actuarial (gain) loss on postretirement benefit obligation included in net income	(73)	(41)	14
Other comprehensive income (loss)	76	(875)	1,417
Comprehensive income including noncontrolling interest	63,880	31,322	54,341
Net comprehensive (income) loss attributable to noncontrolling interest	(2,148)	(449)	489
Comprehensive income attributable to the Association	$ 61,732	$ 30,873	$ 54,830