Consolidated Statements of Revenues and Expenses (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating revenues:
Total operating revenues	$ 460,822	$ 366,239	$ 1,195,280	$ 1,038,857
Operating expenses:
Fuel	214,681	131,925	436,277	282,677
Production	99,321	94,071	298,171	303,705
Depreciation and amortization	69,758	61,758	204,654	186,370
Purchased power	16,920	16,419	50,706	49,366
Accretion	14,117	14,204	41,839	40,830
Total operating expenses	414,797	318,377	1,031,647	862,948
Operating margin	46,025	47,862	163,633	175,909
Other income:
Investment income	12,299	11,672	36,389	36,210
Other	2,516	1,832	4,964	5,733
Total other income	14,815	13,504	41,353	41,943
Interest charges:
Interest expense	105,201	101,600	312,927	305,128
Allowance for debt funds used during construction	(56,179)	(51,518)	(164,628)	(153,595)
Amortization of debt discount and expense	2,911	2,813	8,677	8,482
Net interest charges	51,933	52,895	156,976	160,015
Net margin	8,907	8,471	48,010	57,837
Members
Operating revenues:
Total operating revenues	437,240	365,937	1,171,433	1,038,218
Non-Members
Operating revenues:
Total operating revenues	$ 23,582	$ 302	$ 23,847	$ 639