Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net margin	$ 42,880	$ 43,875
Adjustments to reconcile net margin to net cash provided by operating activities:
Depreciation and amortization, including nuclear fuel	185,640	177,367
Accretion cost	18,109	16,040
Amortization of deferred gains	(894)	(894)
Allowance for equity funds used during construction	(387)	(352)
Deferred outage costs	(22,194)	(26,090)
(Gain) loss on sale of investments	(16,352)	633
Regulatory deferral of costs associated with nuclear decommissioning	5,707	(10,677)
Other	(4,934)	(3,429)
Change in operating assets and liabilities:
Receivables	4,556	(37,697)
Inventories	(6,897)	4,386
Prepayments and other current assets	361	(698)
Accounts payable	21,986	(73,698)
Accrued interest	(31,944)	2,006
Accrued taxes	(2,641)	(3,597)
Other current liabilities	(4,852)	(23,977)
Member power bill prepayments	(48,831)	(24,876)
Total adjustments	96,433	(5,553)
Net cash provided by operating activities	139,313	38,322
Cash flows from investing activities:
Property additions	(474,683)	(301,545)
Activity in nuclear decommissioning trust fund - Purchases	(235,754)	(216,217)
Activity in nuclear decommissioning trust fund - Proceeds	232,376	212,949
Decrease in restricted cash and investments	12,147	31,574
Decrease in restricted short-term investments	61,889	1,340
Activity in other long-term investments - Purchases	(39,042)	(31,114)
Activity in other long-term investments - Proceeds	25,390	24,820
Other	(2,225)	2,494
Net cash used in investing activities	(419,902)	(275,699)
Cash flows from financing activities:
Long-term debt proceeds	4,517	628,358
Long-term debt payments	(240,182)	(75,537)
Increase (decrease) in short-term borrowings, net	425,929	(185,483)
Other	10,141	4,370
Net cash provided by financing activities	200,405	371,708
Net (decrease) increase in cash and cash equivalents	(80,184)	134,331
Cash and cash equivalents at beginning of period	366,290	213,038
Cash and cash equivalents at end of period	286,106	347,369
Cash paid for -
Interest (net of amounts capitalized)	150,849	121,760
Supplemental disclosure of non-cash investing and financing activities:
Change in asset retirement obligations		70,780
Change in accrued property additions	38,038	(38,209)
Interest paid-in-kind	$ 28,092	$ 21,765