Consolidated Statements of Revenues and Expenses - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating revenues:
Total operating revenues	$ 382,623	$ 384,644	$ 1,098,083	$ 1,124,211
Operating expenses:
Fuel	138,704	151,903	349,146	394,494
Production	93,092	95,971	301,996	299,134
Depreciation and amortization	60,574	56,936	183,212	170,565
Purchased power	17,716	15,381	50,415	46,030
Accretion	13,328	9,608	36,361	28,364
Total operating expenses	323,414	329,799	921,130	938,587
Operating margin	59,209	54,845	176,953	185,624
Other income:
Investment income	14,144	15,242	45,129	43,925
Other	623	1,765	1,565	5,383
Total other income	14,767	17,007	46,694	49,308
Interest charges:
Interest expense	100,687	95,958	301,864	280,385
Allowance for debt funds used during construction	(47,909)	(38,589)	(138,246)	(110,670)
Amortization of debt discount and expense	2,912	3,149	8,764	9,198
Net interest charges	55,690	60,518	172,382	178,913
Net margin	18,286	11,334	51,265	56,019
Members
Operating revenues:
Total operating revenues	382,548	384,529	1,097,754	1,123,741
Non-Members
Operating revenues:
Total operating revenues	$ 75	$ 115	$ 329	$ 470