CONSOLIDATED STATEMENTS OF REVENUES AND EXPENSES - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating revenues:
Sales to Members	$ 1,219,052	$ 1,314,869	$ 1,166,618
Sales to non-Members	130,773	93,294	78,758
Total operating revenues	1,349,825	1,408,163	1,245,376
Operating expenses:
Fuel	441,738	515,729	442,425
Production	457,264	428,801	369,730
Depreciation and amortization	168,920	166,247	158,375
Purchased power	56,925	71,799	56,084
Accretion	26,108	24,616	22,900
Deferral of Hawk Road and Smith Energy Facilities effect on net margin	(58,588)	(58,426)	(35,662)
Total operating expenses	1,092,367	1,148,766	1,013,852
Operating margin	257,458	259,397	231,524
Other income:
Investment income	40,424	36,791	33,558
Amortization of deferred gains	1,788	1,788	1,788
Allowance for equity funds used during construction	675	1,172	2,397
Other	9,143	6,620	5,690
Total other income	52,030	46,371	43,433
Interest charges:
Interest expense	354,269	344,561	313,491
Allowance for debt funds used during construction	(108,667)	(102,081)	(95,886)
Amortization of debt discount and expense	15,545	16,653	15,872
Net interest charges	261,147	259,133	233,477
Net margin	$ 48,341	$ 46,635	$ 41,480