Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net margin	$ 48,010	$ 57,837
Adjustments to reconcile net margin to net cash provided by operating activities:
Depreciation and amortization, including nuclear fuel	297,976	278,872
Accretion cost	41,839	40,830
Amortization of deferred gains	(1,341)	(1,341)
Allowance for equity funds used during construction	(267)	(306)
Deferred outage costs	(27,163)	(36,502)
Gain on sale of investments	(11,665)	(14,122)
Regulatory deferral of costs associated with nuclear decommissioning	(15,592)	(11,482)
Other	(639)	(2,566)
Change in operating assets and liabilities:
Receivables	(51,283)	(22,751)
Inventories	46,686	3,836
Prepayments and other current assets	(6,199)	(30,914)
Accounts payable	(4,487)	(28,764)
Accrued interest	5,842	10,483
Accrued taxes	6,788	35,004
Other current liabilities	522	(16,433)
Member power bill prepayments	(31,482)	(56,975)
Rate management program collections	117,600	114,006
Total adjustments	367,135	260,875
Net cash provided by operating activities	415,145	318,712
Cash flows from investing activities:
Property additions	(891,162)	(983,902)
Plant acquisition	233,156	0
Activity in nuclear decommissioning trust fund—Purchases	(556,879)	(393,369)
Activity in nuclear decommissioning trust fund - Proceeds	550,956	387,277
Decrease (increase) in restricted investments	167,607	(7,282)
Activity in other long-term investments—Purchases	(340,877)	(285,842)
Activity in other long-term investments - Proceeds	184,083	136,476
Other	8,139	9,075
Net cash used in investing activities	(1,111,289)	(1,137,567)
Cash flows from financing activities:
Long-term debt proceeds	517,524	2,045,685
Long-term debt payments	(440,548)	(1,274,196)
Increase (decrease) in short-term borrowings, net	639,876	(16,255)
Other	30,124	(1,123)
Net cash provided by financing activities	746,976	754,111
Net increase (decrease) in cash, cash equivalents and restricted cash	50,832	(64,744)
Cash, cash equivalents and restricted cash at beginning of period	405,511	448,612
Cash, cash equivalents and restricted at end of period	456,343	383,868
Cash paid for—
Interest (net of amounts capitalized)	141,206	139,878
Supplemental disclosure of non-cash investing and financing activities:
Change in asset retirement obligations	42,964	22,086
Accrued property additions at end of period	$ 71,443	$ 94,365