Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net margins including noncontrolling interest	$ 63,804	$ 32,197	$ 52,924
Adjustments to reconcile net margins to net cash provided by operating activities:
Depreciation, amortization, and depletion	174,526	173,969	152,718
Amortization of intangible asset	7,324	7,324	7,324
Amortization of NRECA Retirement Security Plan prepayment	5,372	5,372	5,520
Amortization of debt issuance costs	1,985	1,931	1,870
Impairment loss - Holcomb expansion	93,494
Deferred Holcomb expansion impairment loss	(93,494)
Deferred membership withdrawal income		47,572
Recognition of deferred membership withdrawal income	(5,000)
Deferred revenue	9,527
Recognition of deferred revenue	(15,000)	(9,200)
Capital credit allocations from cooperatives and income from coal mines over refund distributions	(4,417)	(17,933)	(7,179)
Proceeds from settlement of interest rate swaps	4,625
Changes in operating assets and liabilities:
Accounts receivable	4,924	(2,417)	10,936
Coal inventory	17,097	(4,668)	(18,604)
Materials and supplies	(1,691)	(2,267)	(5,432)
Accounts payable and accrued expenses	628	3,676	(12,188)
Accrued interest	(1,313)	(166)	1,814
Accrued property taxes	(448)	189	1,385
Other deferred credits - TEP transmission (settlement) refund	(15,521)	15,521
Other deferred credits - BNSF settlement			(29,381)
Other	(6,039)	(288)	21,065
Net cash provided by operating activities	240,383	250,812	182,772
Investing activities
Purchases of plant	(214,781)	(219,771)	(290,428)
Changes in deferred charges	1,112	(298)	9,031
Proceeds from other investments	911	313	321
Net cash used in investing activities	(212,758)	(219,756)	(281,076)
Financing activities
Changes in Member advances	(6,852)	(887)	(7,041)
Payments of long-term debt	(108,301)	(423,957)	(113,063)
Proceeds from issuance of debt	60,000	307,000	240,183
Increase in short-term borrowings, net	24,767	119,901
Retirement of patronage capital	(12,815)	(19,486)	(8,286)
Other	(1,349)	(854)
Net cash provided by (used in) financing activities	(44,550)	(18,283)	111,793
Net increase (decrease) in cash, cash equivalents and restricted cash and investments	(16,925)	12,773	13,489
Cash, cash equivalents and restricted cash and investments – beginning	167,890	155,117	141,628
Cash, cash equivalents and restricted cash and investments – ending	150,965	167,890	155,117
Supplemental cash flow information:
Cash paid for interest	159,112	158,978	154,657
Cash paid for income taxes		1,100
Supplemental disclosure of noncash investing and financing activities:
Change in plant expenditures included in accounts payable	$ (3,242)	$ (1,354)	2,173
Renewal of transmission right of way easements			$ 27,447