Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Revenues
Member electric sales	$ 1,199,940	$ 1,134,781	$ 1,125,699
Non-member electric sales	98,872	119,326	120,234
Other	89,781	86,989	89,515
Total revenues	1,388,593	1,341,096	1,335,448
Operating expenses
Purchased power	339,830	328,407	305,045
Fuel	244,328	235,645	231,537
Production	207,993	218,008	235,398
Transmission	153,510	156,713	153,443
General and administrative	28,704	26,320	24,708
Depreciation, amortization, and depletion	174,526	173,969	152,718
Coal mining	40,034	36,929	36,130
Other	15,971	18,099	18,500
Operating expenses	1,204,896	1,194,090	1,157,479
Operating margins	183,697	147,006	177,969
Other income
Interest	4,723	4,368	4,355
Capital credits from cooperatives	12,934	20,349	9,189
Membership withdrawal	5,000
Other income	3,966	3,934	3,981
Total other income	26,623	28,651	17,525
Interest expense, net of amounts capitalized	147,608	144,877	142,570
Income tax benefit	(1,092)	(1,417)	0
Net margins including noncontrolling interest	63,804	32,197	52,924
Net (income) loss attributable to noncontrolling interest	(2,148)	(449)	489
Net margins attributable to the Association	$ 61,656	$ 31,748	$ 53,413