CONSOLIDATED STATEMENTS OF REVENUES AND EXPENSES - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating revenues:
Total operating revenues	$ 1,604,863	$ 1,377,618	$ 1,430,292
Operating expenses:
Fuel	598,996	360,254	440,214
Production	410,708	427,808	410,328
Depreciation and amortization	275,346	248,888	243,512
Purchased power	69,346	68,484	68,556
Accretion	56,086	54,475	50,473
Total operating expenses	1,410,482	1,159,909	1,213,083
Operating margin	194,381	217,709	217,209
Other income:
Investment income	45,932	43,294	59,182
Amortization of deferred gains	1,789	1,789	1,788
Allowance for equity funds used during construction	385	374	771
Other	23,148	5,238	2,448
Total other income	71,254	50,695	64,189
Interest charges:
Interest expense	417,722	409,145	403,244
Allowance for debt funds used during construction	(221,463)	(207,972)	(187,954)
Amortization of debt discount and expense	11,595	11,336	11,647
Net interest charges	207,854	212,509	226,937
Net margin	57,781	55,895	54,461
Members
Operating revenues:
Total operating revenues	1,557,109	1,377,010	1,429,852
Non-Members
Operating revenues:
Total operating revenues	$ 47,754	$ 608	$ 440