Consolidated Statements of Revenues and Expenses - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating revenues:
Sales to Members	$ 367,073	$ 379,154	$ 721,217	$ 727,251
Sales to non-Members	46	189	72	253
Total operating revenues	367,119	379,343	721,289	727,504
Operating expenses:
Fuel	118,723	126,588	222,638	225,540
Production	99,185	103,180	200,273	206,651
Depreciation and amortization	55,977	54,401	111,840	107,887
Purchased power	14,901	13,002	29,877	26,145
Accretion	9,111	8,024	18,109	16,040
Total operating expenses	297,897	305,195	582,737	582,263
Operating margin	69,222	74,148	138,552	145,241
Other income:
Investment income	14,840	12,727	29,659	25,050
Other	641	2,427	1,281	4,728
Total other income	15,481	15,154	30,940	29,778
Interest charges:
Interest expense	93,527	91,005	186,812	179,522
Allowance for debt funds used during construction	(33,349)	(27,945)	(66,436)	(54,325)
Amortization of debt discount and expense	3,099	2,965	6,236	5,947
Net interest charges	63,277	66,025	126,612	131,144
Net margin	$ 21,426	$ 23,277	$ 42,880	$ 43,875