CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net margin	$ 57,781	$ 55,895	$ 54,461
Adjustments to reconcile net margin to net cash provided by operating activities:
Depreciation and amortization, including nuclear fuel	400,681	376,639	377,853
Accretion cost	56,086	54,475	50,473
Amortization of deferred gains	(1,789)	(1,789)	(1,788)
Allowance for equity funds used during construction	(385)	(374)	(771)
Deferred outage costs	(30,746)	(38,278)	(34,505)
Gain on sale of investments	(13,516)	(19,779)	(6,058)
Gain on sale of spare parts	(15,734)	0	0
Regulatory deferral of costs associated with nuclear decommissioning	(19,318)	(10,691)	(23,982)
Other	(2,528)	(5,587)	(1,097)
Change in operating assets and liabilities:
Receivables	(5,693)	(3,659)	24,251
Inventories	23,232	(2,409)	(18,597)
Prepayments and other current assets	577	(23,754)	(1,992)
Accounts payable	31,790	1,504	(27,668)
Accrued interest	23,976	6,539	4,924
Accrued taxes	(36,301)	33,588	2,943
Other current liabilities	(14,292)	9,439	(24,069)
Member power bill prepayments	(38,078)	(67,281)	(68,245)
Rate management program collections	144,763	146,917	45,228
Total adjustments	502,725	455,500	296,900
Net cash provided by operating activities	560,506	511,395	351,361
Cash flows from investing activities:
Property additions	(1,203,050)	(1,335,380)	(1,255,188)
Plant acquisition	(233,156)	0	0
Activity in nuclear decommissioning trust fund – Purchases	(675,153)	(578,610)	(374,338)
Activity in nuclear decommissioning trust fund - Proceeds	667,344	570,294	365,871
Proceeds from the sale of spare parts	18,500	0	0
Decrease in restricted investments	167,535	46,003	119,568
Activity in other long-term investments – Purchases	(433,532)	(425,628)	(251,077)
Activity in other long-term investments - Proceeds	246,256	186,219	178,172
Other	14,843	7,982	(21,493)
Net cash used in investing activities	(1,430,413)	(1,529,120)	(1,238,485)
Cash flows from financing activities:
Long-term debt proceeds	757,032	2,221,685	1,266,950
Long-term debt payments	(468,577)	(1,334,368)	(523,691)
Increase (decrease) in short-term borrowings, net	712,473	101,128	(154,257)
Other	44,618	(13,821)	(5,884)
Net cash provided by financing activities	1,045,546	974,624	583,118
Net increase (decrease) in cash, cash equivalents and restricted cash	175,639	(43,101)	(304,006)
Cash, cash equivalents and restricted cash at beginning of period	405,511	448,612	752,618
Cash, cash equivalents and restricted cash at end of period	581,150	405,511	448,612
Cash paid for –
Interest (net of amounts capitalized)	170,605	193,063	208,892
Supplemental disclosure of non-cash investing and financing activities:
Change in asset retirement obligations	107,677	18,709	5,282
Accrued property additions at end of period	65,686	89,640	94,492
Interest paid-in-kind	$ 0	$ 0	$ 67,028