CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net margin	$ 48,341	$ 46,635	$ 41,480
Adjustments to reconcile net margin to net cash provided by operating activities:
Depreciation and amortization, including nuclear fuel	313,320	313,449	296,546
Accretion cost	26,108	24,616	22,900
Amortization of deferred gains	(1,788)	(1,788)	(1,788)
Allowance for equity funds used during construction	(675)	(1,172)	(2,397)
Deferred outage costs	(40,803)	(53,823)	(43,302)
Deferral of Hawk Road and Smith Energy Facilities effect on net margin	(58,588)	(58,426)	(35,662)
Gain on sale of investments	(34,464)	(18,179)	(24,962)
Regulatory deferral of costs associated with nuclear decommissioning	21,532	4,564	10,181
Other	(8,353)	(8,835)	(8,718)
Change in operating assets and liabilities:
Receivables	(98)	(1,000)	4,743
Inventories	(28,403)	15,319	(22,219)
Prepayments and other current assets	(4,317)	3,197	191
Accounts payable	(37,155)	(22,488)	(32,665)
Accrued interest	(11)	648	(456)
Accrued and withheld taxes	3,731	(4,198)	17,996
Other current liabilities	2,805	8,956	318
Member power bill prepayments	20,994	83,236	8,787
Total adjustments	173,835	284,076	189,493
Net cash provided by operating activities	222,176	330,711	230,973
Cash flows from investing activities:
Property additions	(495,426)	(534,171)	(628,216)
Activity in nuclear decommissioning trust fund - Purchases	(558,568)	(389,854)	(568,979)
Activity in nuclear decommissioning trust fund - Proceeds	553,654	385,185	563,712
Increase in restricted cash and investments	(16,301)	(57,815)	(51,622)
(Increase) decrease in restricted cash and short-term investments	(6,076)	48	(182,415)
Activity in other long-term investments - Purchases	(89,263)	(54,113)	(40,593)
Activity in other long-term investments - Proceeds	86,563	53,756	41,652
Activity on interest rate options - Purchases/Collateral returned		(81,070)	(187,190)
Activity on interest rate options - Collateral received		46,100	213,210
Other	(13,068)	(44,893)	6,626
Net cash used in investing activities	(538,485)	(676,827)	(833,815)
Cash flows from financing activities:
Long-term debt proceeds	423,637	1,135,687	888,857
Long-term debt payments	(162,903)	(408,377)	(351,273)
Increase (decrease) in short-term borrowings, net	27,109	(510,038)	174,927
Other	4,113	(41,958)	(41)
Net cash provided by financing activities	291,956	175,314	712,470
Net (decrease) increase in cash and cash equivalents	(24,353)	(170,802)	109,628
Cash and cash equivalents at beginning of period	237,391	408,193	298,565
Cash and cash equivalents at end of period	213,038	237,391	408,193
Cash paid for -
Interest (net of amounts capitalized)	240,817	237,107	213,404
Supplemental disclosure of non-cash investing and financing activities:
Change in asset retirement obligations	144,161
Change in accrued property additions	119,775	36,633	$ (3,473)
Interest paid-in-kind	$ 36,021	$ 24,607