CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net Margin	$ 50,345	$ 48,341	$ 46,635
Adjustments to reconcile net margin to net cash provided by operating activities:
Depreciation and amortization, including nuclear fuel	362,716	313,320	313,449
Accretion cost	32,361	26,108	24,616
Amortization of deferred gains	(1,788)	(1,788)	(1,788)
Allowance for equity funds used during construction	(788)	(675)	(1,172)
Deferred outage costs	(40,599)	(40,803)	(53,823)
Deferral of Hawk Road and Smith Energy Facilities effect on net margin	0	(58,588)	(58,426)
Loss (gain) on sale of investments	96	(34,464)	(18,179)
Regulatory deferral of costs associated with nuclear decommissioning	(20,440)	21,532	4,564
Other	(7,286)	(8,353)	(8,835)
Change in operating assets and liabilities:
Receivables	(24,578)	(98)	(1,000)
Inventories	23,947	(28,403)	15,319
Prepayments and other current assets	(2,172)	(4,317)	3,197
Accounts payable	(76,495)	(37,155)	(22,488)
Accrued interest	34,804	(11)	648
Accrued and withheld taxes	1,102	3,731	(4,198)
Other current liabilities	(11,937)	2,805	8,956
Member power bill prepayments	6,155	20,994	83,236
Total adjustments	275,098	173,835	284,076
Net cash provided by operating activities	325,443	222,176	330,711
Cash flows from investing activities:
Property additions	(613,019)	(495,426)	(534,171)
Activity in nuclear decommissioning trust fund - Purchases	(395,506)	(558,568)	(389,854)
Activity in nuclear decommissioning trust fund - Proceeds	389,011	553,654	385,185
Increase in restricted cash and investments	(86,432)	(16,301)	(57,815)
Decrease (increase) in restricted short-term investments	(6,198)	6,076	(48)
Activity in other long-term investments - Purchases	(61,200)	(89,263)	(54,113)
Activity in other long-term investments - Proceeds	50,529	86,563	53,756
Activity on interest rate options - Purchases/Collateral returned	0	0	(81,070)
Activity on interest rate options - Collateral received	0	0	46,100
Other	13,554	(13,068)	(44,893)
Net cash used in investing activities	(696,865)	(538,485)	(676,827)
Cash flows from financing activities:
Long-term debt proceeds	790,385	423,637	1,135,687
Long-term debt payments	(114,702)	(162,903)	(408,377)
(Decrease) increase in short-term borrowings, net	(159,310)	27,109	(510,038)
Other	8,301	4,113	(41,958)
Net cash provided by financing activities	524,674	291,956	175,314
Net increase (decrease) in cash and cash equivalents	153,252	(24,353)	(170,802)
Cash and cash equivalents at beginning of period	213,038	237,391	408,193
Cash and cash equivalents at end of period	366,290	213,038	237,391
Cash paid for -
Interest (net of amounts capitalized)	212,574	240,817	237,107
Supplemental disclosure of non-cash investing and financing activities:
Change in asset retirement obligations	63,011	144,161
Change in accrued property additions	(50,775)	119,775	36,633
Interest paid-in-kind	$ 47,814	$ 36,021	$ 24,607