Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net margin	$ 27,400	$ 21,454
Adjustments to reconcile net margin to net cash provided by operating activities:
Depreciation and amortization, including nuclear fuel	91,608	92,049
Accretion cost	9,320	8,998
Amortization of deferred gains	(447)	(447)
Allowance for equity funds used during construction	(209)	(193)
Deferred outage costs	(11,331)	(19,385)
Loss (gain) on sale of investments	1,290	(16,045)
Regulatory deferral of costs associated with nuclear decommissioning	(6,835)	10,602
Other	(1,394)	(3,138)
Change in operating assets and liabilities:
Receivables	30,958	6,241
Inventories	(5,406)	(12,028)
Prepayments and other current assets	1,646	3,822
Accounts payable	(55,431)	(18,028)
Accrued interest	(1,058)	(35,292)
Accrued taxes	(10,338)	(12,909)
Other current liabilities	(4,126)	(7,059)
Member power bill prepayments	8,661	1,717
Total adjustments	46,908	(1,095)
Net cash provided by operating activities	74,308	20,359
Cash flows from investing activities:
Property additions	(285,374)	(171,806)
Activity in nuclear decommissioning trust fund - Purchases	(122,330)	(165,213)
Activity in nuclear decommissioning trust fund - Proceeds	120,409	163,635
Decrease in restricted investments	39,997	36,990
Increase in restricted short-term investments	(10,168)	(3)
Activity in other long-term investments - Purchases	(43,844)	(18,190)
Activity in other long-term investments - Proceeds	38,063	14,093
Other	8,167	(1,658)
Net cash used in investing activities	(255,080)	(142,152)
Cash flows from financing activities:
Long-term debt proceeds	2,636	4,517
Long-term debt payments	(39,350)	(201,398)
Increase in short-term borrowings, net	68,171	226,722
Other	730	4,213
Net cash provided by financing activities	32,187	34,054
Net decrease in cash and cash equivalents	(148,585)	(87,739)
Cash and cash equivalents at beginning of period	397,695	366,290
Cash and cash equivalents at end of period	249,110	278,551
Cash paid for -
Interest (net of amounts capitalized)	55,772	94,754
Supplemental disclosure of non-cash investing and financing activities:
Accrued property additions at end of period	133,318	67,128
Interest paid-in-kind	$ 14,393	$ 13,909