Consolidated Statements of Revenues and Expenses - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating revenues:
Total operating revenues	$ 365,921	$ 361,369	$ 739,567	$ 715,539
Operating expenses:
Fuel	122,144	118,723	242,591	222,638
Production	101,891	99,185	203,163	200,273
Depreciation and amortization	56,841	55,977	113,629	111,840
Purchased power	14,761	14,901	30,649	29,877
Accretion	9,435	9,111	18,756	18,109
Total operating expenses	305,072	297,897	608,788	582,737
Operating margin	60,849	63,472	130,779	132,802
Other income:
Investment income	14,719	14,840	28,683	29,659
Other	1,643	641	3,617	1,281
Total other income	16,362	15,481	32,300	30,940
Interest charges:
Interest expense	91,825	93,527	181,495	186,812
Allowance for debt funds used during construction	(34,950)	(33,349)	(69,149)	(66,436)
Amortization of debt discount and expense	3,051	3,099	6,049	6,236
Net interest charges	59,926	63,277	118,395	126,612
Net margin	17,285	15,676	44,684	37,130
Members
Operating revenues:
Total operating revenues	365,811	361,323	739,212	715,467
Non-Members
Operating revenues:
Total operating revenues	$ 110	$ 46	$ 355	$ 72