El Paso Electric 10-Q 4 Aug 17 2017 Q2 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	6 Months Ended
	Jun. 30, 2017	Jul. 31, 2017
Document and Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q2
Trading Symbol	ee
Entity Registrant Name	EL PASO ELECTRIC CO /TX/
Entity Central Index Key	31,978
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		40,591,704

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Utility plant:
Electric plant in service	$ 3,893,461	$ 3,791,566
Less accumulated depreciation and amortization	(1,282,795)	(1,244,332)
Net plant in service	2,610,666	2,547,234
Construction work in progress	146,615	154,738
Nuclear fuel; includes fuel in process of $59,954 and $57,315, respectively	196,054	194,842
Less accumulated amortization	(74,566)	(75,602)
Net nuclear fuel	121,488	119,240
Net utility plant	2,878,769	2,821,212
Current assets:
Cash and cash equivalents	11,275	8,420
Accounts receivable, principally trade, net of allowance for doubtful accounts of $1,682 and $2,156, respectively	124,616	88,452
Inventories, at cost	50,929	47,216
Under-collection of fuel revenues	8,515	11,123
Prepayments and other	13,727	8,988
Total current assets	209,062	164,199
Deferred charges and other assets:
Decommissioning trust funds	271,315	255,708
Regulatory assets	115,245	118,861
Other	17,002	16,298
Total deferred charges and other assets	403,562	390,867
Total assets	3,491,393	3,376,278
Capitalization:
Common stock, stated value $1 per share, 100,000,000 shares authorized, 65,659,869 and 65,685,615 shares issued, and 169,565 and 137,017 restricted shares, respectively	65,829	65,823
Capital in excess of stated value	323,779	322,643
Retained earnings	1,120,664	1,114,561
Accumulated other comprehensive loss, net of tax	(4,133)	(7,116)
Total stockholders' equity subtotal before treasury stock	1,506,139	1,495,911
Treasury stock, 25,232,769 and 25,304,914 shares, respectively, at cost	(420,313)	(421,515)
Common stock equity	1,085,826	1,074,396
Long-term debt, net of current portion	1,195,748	1,195,513
Total capitalization	2,281,574	2,269,909
Current liabilities:
Current maturities of long-term debt	83,268	83,143
Short-term borrowings under the revolving credit facility	178,884	81,574
Accounts payable, principally trade	52,586	62,953
Taxes accrued	27,772	32,488
Interest accrued	13,373	13,287
Over-collection of fuel revenues	314	255
Other	33,239	29,709
Total current liabilities	389,436	303,409
Deferred credits and other liabilities:
Accumulated deferred income taxes	564,377	555,066
Accrued pension liability	87,460	92,768
Accrued post-retirement benefit liability	35,703	34,400
Asset retirement obligation	89,199	81,800
Regulatory liabilities	22,253	18,435
Other	21,391	20,491
Total deferred credits and other liabilities	820,383	802,960
Commitments and contingencies
Total capitalization and liabilities	$ 3,491,393	$ 3,376,278

Balance Sheets Parenthetical

Balance Sheets Parenthetical - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Nuclear fuel; fuel in process	$ 59,954	$ 57,315
Allowance for Doubtful Accounts Receivable, Current	$ 1,682	$ 2,156
Common Stock, Par or Stated Value Per Share	$ 1	$ 1
Common Stock, Shares Authorized	100,000,000	100,000,000
Common Stock, Shares, Issued	65,659,869	65,685,615
Common stock, restricted shares	169,565	137,017
Treasury Stock, Shares	25,232,769	25,304,914

Statements Of Operations

Statements Of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating revenues	$ 251,843	$ 217,865	$ 423,178	$ 375,674	$ 934,440	$ 842,289
Energy expenses:
Fuel	49,173	43,143	85,779	77,462	182,055	178,320
Purchased and interchanged power	16,721	13,610	30,394	23,256	66,865	53,884
Cost of services, energy services	65,894	56,753	116,173	100,718	248,920	232,204
Operating revenues net of energy expenses	185,949	161,112	307,005	274,956	685,520	610,085
Other operating expenses:
Other operations	59,835	56,817	115,958	115,204	242,768	244,899
Maintenance	20,415	20,426	41,405	37,941	70,210	67,747
Depreciation and amortization	22,495	23,852	44,429	47,145	81,601	92,269
Taxes other than income taxes	17,265	15,320	32,995	30,132	68,396	64,277
Utilities operating expense	120,010	116,415	234,787	230,422	462,975	469,192
Operating income	65,939	44,697	72,218	44,534	222,545	140,893
Other income (deductions):
Allowance for equity funds used during construction	726	2,133	1,541	4,469	4,095	8,565
Investment and interest income, net	6,786	3,591	10,772	6,520	18,335	17,376
Miscellaneous non-operating income	39	145	124	801	615	2,176
Miscellaneous non-operating deductions	(530)	(890)	(1,270)	(1,356)	(3,613)	(3,922)
Nonoperating income	7,021	4,979	11,167	10,434	19,432	24,195
Interest charges (credits):
Interest on long-term debt and revolving credit facility	18,407	18,298	36,774	34,897	73,421	67,770
Other interest	762	272	1,182	834	1,651	1,630
Capitalized interest	(1,344)	(1,253)	(2,638)	(2,495)	(5,133)	(4,913)
Allowance for borrowed funds used during construction	(711)	(1,375)	(1,502)	(3,033)	(3,452)	(5,958)
Interest expense	17,114	15,942	33,816	30,203	66,487	58,529
Income before income taxes	55,846	33,734	49,569	24,765	175,490	106,559
Income tax expense	19,780	11,450	17,492	8,289	63,121	32,695
Net income	$ 36,066	$ 22,284	$ 32,077	$ 16,476	$ 112,369	$ 73,864
Basic earnings per share	$ 0.890	$ 0.550	$ 0.790	$ 0.410	$ 2.770	$ 1.830
Diluted earnings per share	0.890	0.550	0.790	0.410	2.770	1.830
Dividends declared per share of common stock	$ 0.335	$ 0.310	$ 0.645	$ 0.605	$ 1.265	$ 1.195
Weighted average number of shares outstanding	40,409,030	40,345,150	40,398,192	40,335,236	40,381,776	40,314,032
Weighted average number of shares and dilutive potential shares outstanding	40,525,585	40,399,491	40,499,344	40,380,640	40,466,995	40,356,239

Statements Of Comprehensive Ope

Statements Of Comprehensive Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net income	$ 36,066	$ 22,284	$ 32,077	$ 16,476	$ 112,369	$ 73,864
Unrecognized pension and post-retirement benefit costs:
Net (loss) gain arising during period	0	0	0	0	(20,053)	5,429
Prior service benefit	0	0	0	0	32,697	824
Reclassification adjustments included in net income for amortization of:
Prior service benefit	(2,413)	(1,664)	(4,829)	(3,330)	(8,906)	(6,579)
Net loss	1,694	1,222	3,388	2,445	5,908	6,567
Net unrealized gains on marketable securities:
Net holding gains arising during period	4,458	2,790	12,179	4,980	15,643	2,623
Reclassification adjustments for net gains included in net income	(5,166)	(2,110)	(7,357)	(3,498)	(11,499)	(11,049)
Net losses on cash flow hedges:
Reclassification adjustment for interest expense included in net income	132	123	262	245	515	482
Total other comprehensive (loss) income before income taxes	(1,295)	361	3,643	842	14,305	(1,703)
Income tax benefit (expense) related to items of other comprehensive (loss) income:
Unrecognized pension and post-retirement benefit costs	261	166	454	222	(4,029)	(2,442)
Net unrealized losses (gains) on marketable securities	132	(149)	(989)	(322)	(773)	1,625
Losses on cash flow hedges	(47)	(46)	(125)	(128)	(336)	(216)
Total income tax benefit (expense)	346	(29)	(660)	(228)	(5,138)	(1,033)
Other comprehensive (loss) income, net of tax	(949)	332	2,983	614	9,167	(2,736)
Comprehensive income	$ 35,117	$ 22,616	$ 35,060	$ 17,090	$ 121,536	$ 71,128

Statements Of Cash Flows

Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net income	$ 32,077	$ 16,476
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of electric plant in service	44,429	47,145
Amortization of nuclear fuel	21,100	21,957
Deferred income taxes, net	15,339	6,695
Allowance for equity funds used during construction	(1,541)	(4,469)
Other amortization and accretion	9,991	8,715
Gain on sale of property, plant and equipment	0	(545)
Net gains on sale of decommissioning trust funds	(7,357)	(3,498)
Other operating activities	(641)	721
Change in:
Accounts receivable	(32,684)	(39,117)
Inventories	(2,791)	1,315
Net under/over-collection of fuel revenues	2,667	(1,990)
Prepayments and other	(6,294)	(6,273)
Accounts payable	(1,262)	(9,345)
Taxes accrued	(4,014)	(5,437)
Interest accrued	86	618
Other current liabilities	3,530	13,625
Deferred charges and credits	(4,644)	(5,900)
Net cash provided by operating activities	67,991	40,693
Cash flows from investing activities:
Cash additions to utility property, plant and equipment	(108,113)	(102,785)
Cash additions to nuclear fuel	(20,647)	(20,478)
Capitalized interest and AFUDC:
Utility property, plant and equipment	(3,043)	(7,502)
Nuclear fuel and other	(2,638)	(2,495)
Allowance for equity funds used during construction	1,541	4,469
Decommissioning trust funds:
Purchases, including funding of $2.3 million and $2.2 million, respectively	(65,960)	(44,937)
Sales and maturities	62,531	40,712
Proceeds from sale of property, plant, and equipment	0	596
Other investing activities	797	2,771
Net cash used for investing activities	(135,532)	(129,649)
Cash flows from financing activities:
Dividends paid	(26,157)	(24,474)
Borrowings under the revolving credit facility:
Proceeds	292,404	172,125
Payments	(195,094)	(212,249)
Proceeds from issuance of senior notes	0	157,052
Other financing activities	(757)	(2,040)
Net cash provided by financing activities	70,396	90,414
Net increase in cash and cash equivalents	2,855	1,458
Cash and cash equivalents at beginning of period	8,420	8,149
Cash and cash equivalents at end of period	$ 11,275	$ 9,607

Statements Of Cash Flows Parent

Statements Of Cash Flows Parenthetical - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Payments To Fund Decommissioning Fund	$ 2.3	$ 2.2

Principles Of Preparation

Principles Of Preparation	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Principles Of Preparation	Principles of Preparation These condensed financial statements should be read in conjunction with the financial statements and notes thereto in the Annual Report of El Paso Electric Company on Form 10-K for the fiscal year ended December 31, 2016 (" 2016 Form 10-K"). Capitalized terms used in this report and not defined herein have the meaning ascribed to such terms in the 2016 Form 10-K. In the opinion of the Company’s management, the accompanying financial statements contain all adjustments necessary to present fairly the financial position of the Company at June 30, 2017 and December 31, 2016 ; the results of its operations and comprehensive operations for the three, six and twelve months ended June 30, 2017 and 2016 ; and its cash flows for the six months ended June 30, 2017 and 2016 . The results of operations and comprehensive operations for the three and six months ended June 30, 2017 and 2016 , and the cash flows for the six months ended June 30, 2017 and 2016 , are not necessarily indicative of the results to be expected for the full calendar year. Pursuant to the rules and regulations of the Securities and Exchange Commission ("SEC"), certain financial information has been condensed and certain footnote disclosures have been omitted. Such information and disclosures are normally included in financial statements prepared in accordance with Generally Accepted Accounting Principles ("GAAP"). Use of Estimates . The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. The Company evaluates its estimates on an on-going basis, including those related to depreciation, unbilled revenue, income taxes, fuel costs, pension and other post-retirement obligations and asset retirement obligations ("ARO"). Actual results could differ from those estimates. Revenues . Revenues related to the sale of electricity are generally recorded when service is provided or electricity is delivered to customers. The billing of electricity sales to retail customers is based on the reading of their meters, which occurs on a systematic basis throughout the month. Unbilled revenues are recorded for estimated amounts of energy delivered in the period following the customer's billing cycle to the end of the month. Unbilled revenues are estimated based on monthly generation volumes and by applying an average revenue/kWh to the number of estimated kWhs delivered but not billed. Accounts receivable included accrued unbilled revenues of $36.1 million at June 30, 2017 and $21.0 million at December 31, 2016 . The Company presents revenues net of sales taxes in its statements of operations. Depreciation. The Company routinely evaluates the depreciable service lives, cost of removal and salvage values of its property, plant and equipment. Depreciation is provided on a straight-line basis over the estimated remaining lives of the assets (ranging in average from 5 to 48 years). When property subject to composite depreciation is retired or otherwise disposed of in the normal course of business, its cost, together with the cost of removal, less salvage, is charged to accumulated depreciation. For other property dispositions, the applicable cost and accumulated depreciation is removed from the balance sheet accounts and a gain or loss is recognized. New Accounting Standards In March 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2016-09, Compensation - Stock Compensation (Topic 718) Improvements to Employee Share-Based Payment Accounting to simplify the accounting for share-based payment transactions, including the income tax consequences, classification of awards either as equity or liabilities, and classification on the statements of cash flows. The Company adopted the new standard effective January 1, 2017. The adoption of the new standard did not have a material impact on the Company’s financial condition, results of operations or cash flows. The cumulative effect of the adoption of the new standard was to increase net operating loss carryforward deferred tax assets and retained earnings by $0.2 million on January 1, 2017. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) to provide a framework that replaces the existing revenue recognition guidance, and has since modified the standard with several ASUs. The standard provides that an entity should recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. More specifically, the standard requires entities to recognize revenue through the application of a five-step model, which includes the: (i) identification of the contract; (ii) identification of the performance obligations; (iii) determination of the transaction price; (iv) allocation of the transaction price to the performance obligations; and (v) the recognition of revenue as the entity satisfies the performance obligations. The Company plans to adopt the new standard for reporting periods beginning after December 15, 2017. The Company currently anticipates using the modified retrospective approach. The Company is currently in the process of evaluating the impact of the new standard on its various revenue and cash flow streams, including the evaluation of the impact, if any, on changes to business processes, systems and controls to support recognition and disclosure under the new guidance. Tariff sales to customers are determined to be in the scope of the new standard and represent a significant portion of the Company’s total operating revenues. The Company currently expects that the timing or pattern of revenue recognition from tariff sales will not significantly change. The Company's evaluation of other revenue streams is ongoing. The Company's initial assessments may change as it executes its implementation plan and new guidance is provided by the American Institute of Certified Public Accountants Power and Utilities Industry Task Force. The completion of these assessments could impact current accounting policies, revenue recognition and disclosures in the notes to the financial statements. In January 2016, the FASB issued ASU 2016-01, Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Liabilities to enhance the reporting model for financial instruments by addressing certain aspects of recognition, measurement, presentation, and disclosure. ASU 2016-01 generally requires entities to measure equity investments that do not result in consolidation and are not accounted for under the equity method at fair value and recognize any changes in fair value in net income. The guidance for classifying and measuring investments in debt securities and loans is not changed by this ASU, but requires entities to record changes in other comprehensive income. Financial assets and financial liabilities must be separately presented by measurement category on the balance sheet or in the accompanying notes to the financial statements. ASU 2016-01 clarifies the need for a valuation allowance on a deferred tax asset related to available-for-sale securities in combination with the entity's other deferred tax assets. The provisions of this ASU become effective for reporting periods beginning after December 15, 2017. Upon adoption of the new standard, the Company expects to record the cumulative effects as of January 1, 2018 which will result in an adjustment to accumulated other comprehensive income (losses) and retained earnings for unrealized gains (losses) related to equity securities owned by the Company. The Company is continuing to assess the future impact of this ASU. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) to increase transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and requiring qualitative and quantitative disclosures on leasing agreements. ASU 2016-02 maintains a distinction between finance leases and operating leases similar to the distinction under previous leases guidance for capital leases and operating leases. The impact of leases reported in the Company's operating results and statement of cash flows are expected to be similar to previous GAAP. ASU 2016-02 requires the recognition in the statement of financial position, by the lessee, of a liability to make lease payments (lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term. How leases are recorded in regard to financial position represents a significant change from previous GAAP guidance. The lessee is permitted to make an accounting policy election to not recognize lease assets and lease liabilities for short-term leases. Implementation of the standard will be required for reporting periods beginning after December 15, 2018. Adoption of the new lease accounting standard will require the Company to apply the new standard to the earliest period using a modified retrospective approach. The Company is currently in the process of evaluating the impact of the new standard, including the evaluation of the impact, if any, on changes to business processes, systems and controls to support recognition and disclosure under the new guidance, however, at this time is unable to determine the impact this standard will have on the financial statements and related disclosures. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326). ASU 2016-13 changes how companies measure and recognize credit impairment for many financial assets. The new current expected credit loss model will require companies to immediately recognize an estimate of credit losses expected to occur over the remaining life of the financial assets that are in the scope of the standard. The ASU also makes targeted amendments to the current impairment model for available-for-sale debt securities. The provisions in ASU 2016-13 will be required for reporting periods beginning after December 15, 2019. ASU 2016-13 will be applied in a modified-retrospective approach through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is implemented. The Company is currently assessing the future impact of ASU 2016-13. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230) Classification of Certain Cash Receipts and Cash Payments to reduce diversity in practice in how certain cash receipts and cash payments are classified in the statement of cash flows. The provisions in ASU 2016-15 will be required for reporting periods beginning after December 15, 2017. ASU 2016-15 will be applied using a retrospective transition method to each period presented. If it is impracticable to apply ASU 2016-15 retrospectively for some of the issues, the amendments for those issues may be applied prospectively as of the earliest date practicable. The Company is currently assessing the future impact of this ASU. In March 2017, the FASB issued ASU 2017-07, Compensation-Retirement Benefits (Topic 715) Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. ASU 2017-07 amends Accounting Standards Codification 715, Compensation - Retirement Benefits, to require companies to present the service cost component of net benefit cost in the income statement line items where compensation cost is reported. Companies will present all other components of net benefit cost separately from the line item(s) that includes the service cost and outside of any subtotal of operating income. In addition, only the service cost component will be eligible for capitalization in assets. The amendments in ASU 2017-07 will be required for reporting periods beginning after December 15, 2017. The amendments in ASU 2017-07 should be applied retrospectively for the income statement presentation of the service cost component and the other components of net benefit costs and prospectively, on and after the effective date, for the capitalization of the service cost component. The Company is currently assessing the future impact of this ASU. In May 2017, the FASB issued ASU 2017-09, Compensation-Stock Compensation (Topic 718), Scope of Modification Accounting, to provide guidance about when to account for a change to the terms or conditions of a share-based payment award as a modification. Under ASU 2017-09, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award (as equity or liability) changes as a result of the change in terms or conditions. The amendments of ASU 2017-09 will be required for reporting periods beginning after December 15, 2017. ASU 2017-09 should be applied prospectively to an award modified on or after the adoption date. The Company is assessing the future impact of ASU 2017-09; however, it currently does not expect the impact of this ASU to be significant. Supplemental Cash Flow Disclosures (in thousands) Six Months Ended June 30, 2017 2016 Cash paid (received) for: Interest on long-term debt and borrowings under the revolving credit facility $ 35,304 $ 35,252 Income tax paid, net 2,251 2,703 Non-cash investing and financing activities: Changes in accrued plant additions (9,105 ) (6,966 ) Plant additions to be reimbursed by insurance 3,525 — Grants of restricted shares of common stock 1,171 1,236 Issuance of performance shares 932 —

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Notes)	6 Months Ended
	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Comprehensive Income (Loss) Note	Accumulated Other Comprehensive Income (Loss) Changes in Accumulated Other Comprehensive Income (Loss) (net of tax) by component are presented below (in thousands): Three Months Ended June 30, 2017 Three Months Ended June 30, 2016 Unrecognized Pension and Post-retirement Benefit Costs Net Unrealized Gains (Losses) on Marketable Securities Net Losses on Cash Flow Hedges Accumulated Other Comprehensive Income (Loss) Unrecognized Pension and Post-retirement Benefit Costs Net Unrealized Gains (Losses) on Marketable Securities Net Losses on Cash Flow Hedges Accumulated Other Comprehensive Income (Loss) Balance at beginning of period $ (24,457 ) $ 32,872 $ (11,599 ) $ (3,184 ) $ (30,256 ) $ 28,394 $ (11,770 ) $ (13,632 ) Other comprehensive income before reclassifications — 3,558 — 3,558 — 2,224 — 2,224 Amounts reclassified from accumulated other comprehensive income (loss) (458 ) (4,134 ) 85 (4,507 ) (276 ) (1,693 ) 77 (1,892 ) Balance at end of period $ (24,915 ) $ 32,296 $ (11,514 ) $ (4,133 ) $ (30,532 ) $ 28,925 $ (11,693 ) $ (13,300 ) Six Months Ended June 30, 2017 Six Months Ended June 30, 2016 Unrecognized Pension and Post-retirement Benefit Costs Net Unrealized Gains (Losses) on Marketable Securities Net Losses on Cash Flow Hedges Accumulated Other Comprehensive Income (Loss) Unrecognized Pension and Post-retirement Benefit Costs Net Unrealized Gains (Losses) on Marketable Securities Net Losses on Cash Flow Hedges Accumulated Other Comprehensive Income (Loss) Balance at beginning of period $ (23,928 ) $ 28,463 $ (11,651 ) $ (7,116 ) $ (29,869 ) $ 27,765 $ (11,810 ) $ (13,914 ) Other comprehensive income before reclassifications — 9,723 — 9,723 — 3,966 — 3,966 Amounts reclassified from accumulated other comprehensive income (loss) (987 ) (5,890 ) 137 (6,740 ) (663 ) (2,806 ) 117 (3,352 ) Balance at end of period $ (24,915 ) $ 32,296 $ (11,514 ) $ (4,133 ) $ (30,532 ) $ 28,925 $ (11,693 ) $ (13,300 ) Twelve Months Ended June 30, 2017 Twelve Months Ended June 30, 2016 Unrecognized Pension and Post-retirement Benefit Costs Net Unrealized Gains (Losses) on Marketable Securities Net Losses on Cash Flow Hedges Accumulated Other Comprehensive Income (Loss) Unrecognized Pension and Post-retirement Benefit Costs Net Unrealized Gains (Losses) on Marketable Securities Net Losses on Cash Flow Hedges Accumulated Other Comprehensive Income (Loss) Balance at beginning of period $ (30,532 ) $ 28,925 $ (11,693 ) $ (13,300 ) $ (34,331 ) $ 35,726 $ (11,959 ) $ (10,564 ) Other comprehensive income before reclassifications 7,363 12,661 — 20,024 3,777 2,080 — 5,857 Amounts reclassified from accumulated other comprehensive income (loss) (1,746 ) (9,290 ) 179 (10,857 ) 22 (8,881 ) 266 (8,593 ) Balance at end of period $ (24,915 ) $ 32,296 $ (11,514 ) $ (4,133 ) $ (30,532 ) $ 28,925 $ (11,693 ) $ (13,300 ) Amounts reclassified from Accumulated Other Comprehensive Income (Loss) for the three, six and twelve months ended June 30, 2017 and 2016 are as follows (in thousands): Details about Accumulated Other Comprehensive Income (Loss) Components Three Months Ended June 30, Six Months Ended June 30, Twelve Months Ended June 30, Affected Line Item in the Statement of Operations 2017 2016 2017 2016 2017 2016 Amortization of pension and post-retirement benefit costs: Prior service benefit $ 2,413 $ 1,664 $ 4,829 $ 3,330 $ 8,906 $ 6,579 (a) Net loss (1,694 ) (1,222 ) (3,388 ) (2,445 ) (5,908 ) (6,567 ) (a) 719 442 1,441 885 2,998 12 (a) Income tax effect (261 ) (166 ) (454 ) (222 ) (1,252 ) (34 ) Income tax benefit 458 276 987 663 1,746 (22 ) Net income (loss) Marketable securities: Net realized gain on sale of securities 5,166 2,110 7,357 3,498 11,499 11,049 Investment and interest income, net 5,166 2,110 7,357 3,498 11,499 11,049 Income before income taxes Income tax effect (1,032 ) (417 ) (1,467 ) (692 ) (2,209 ) (2,168 ) Income tax benefit 4,134 1,693 5,890 2,806 9,290 8,881 Net income Loss on cash flow hedge: Amortization of loss (132 ) (123 ) (262 ) (245 ) (515 ) (482 ) Interest on long-term debt and revolving credit facility (132 ) (123 ) (262 ) (245 ) (515 ) (482 ) Loss before income taxes Income tax effect 47 46 125 128 336 216 Income tax expense (85 ) (77 ) (137 ) (117 ) (179 ) (266 ) Net loss Total reclassifications $ 4,507 $ 1,892 $ 6,740 $ 3,352 $ 10,857 $ 8,593 (a) These items are included in the computation of net periodic benefit cost. See Note I, Employee Benefits, for additional information.

Regulation

Regulation	6 Months Ended
	Jun. 30, 2017
Public Utilities, General Disclosures [Abstract]
Regulation	Regulation General The rates and services of the Company are regulated by incorporated municipalities in Texas, the Public Utility Commission of Texas ("PUCT"), the New Mexico Public Regulation Commission ("NMPRC"), and the Federal Energy Regulatory Commission ("FERC"). Municipal orders, ordinances and other agreements regarding rates and services adopted by Texas municipalities are subject to review and approval by the PUCT. The FERC has jurisdiction over the Company's wholesale (sales for resale) transactions, transmission service and compliance with federally-mandated reliability standards. The decisions of the PUCT, the NMPRC and the FERC are subject to judicial review. Texas Regulatory Matters 2015 Texas Retail Rate Case Filing. On August 10, 2015, the Company filed with the City of El Paso, other municipalities incorporated in its Texas service territory, and the PUCT in Docket No. 44941, a request for an annual increase in non-fuel base revenues ("2015 Texas Retail Rate Case"). On July 21, 2016, the parties to PUCT Docket No. 44941 filed the Joint Motion to Implement Uncontested Amended and Restated Stipulation and Agreement which was unopposed by the parties ("Unopposed Settlement"). On August 25, 2016, the PUCT approved the Unopposed Settlement and issued its final order in Docket No. 44941 ("PUCT Final Order"), as proposed. The PUCT Final Order provided for: (i) an annual non-fuel base rate increase, lower annual depreciation expense, a revised return on equity for allowance for funds used during construction ("AFUDC") purposes, and the inclusion of substantially all new plant in service in rate base; (ii) an additional annual non-fuel base rate increase of $3.7 million related to Four Corners Generating Station ("Four Corners") costs, which will be collected through a surcharge terminating on July 11, 2017 ; (iii) removing the separate rate treatment for residential customers with solar systems that the Company had proposed in its August 10, 2015 filing; (iv) allowing the Company to recover $3.1 million in rate case expenses through a separate surcharge and (v) allowing the Company to recover revenues associated with the relate back of rates to consumption on and after January 12, 2016 through March 31, 2016 through a separate surcharge. Interim rates associated with the annual non-fuel base rate increase, became effective on April 1, 2016 . The additional surcharges associated with the incremental Four Corners costs, rate case expenses and the relate back of rates to consumption on and after January 12, 2016 through March 31, 2016 were implemented on October 1, 2016 . For financial reporting purposes, the Company deferred any recognition of the Company's request in its 2015 Texas Retail Rate Case until it received the PUCT Final Order on August 25, 2016 . Accordingly, it reported in the third quarter of 2016 the cumulative effect of the PUCT Final Order which related back to January 12, 2016. 2017 Texas Retail Rate Case Filing. On February 13, 2017, the Company filed with the City of El Paso, other municipalities incorporated in the Company's Texas service territory and the PUCT in Docket No. 46831, a request for an increase in non-fuel base revenues of approximately $42.5 million . On May 16, 2017, the Company filed a motion to sever rate case expense issues from the main rate case. The request was approved by the Administrative Law Judges, initiating Docket No. 47228, on June 5, 2017. On July 21, 2017, the Company filed its rebuttal testimony modifying the requested increase to $39.2 million . The decrease from the original request related primarily to the transfer of the recovery of $3.0 million of the rate case expenses to a separate proceeding as noted above. Hearings on the merits of the rate case are scheduled to begin on August 21, 2017. The Company requested, pursuant to its statutory right, to have its new rates relate back for consumption on and after July 18, 2017, which is the 155 th day after the filing of the rate case. The difference in rates that would have been billed will be surcharged or refunded to customers after the PUCT's final order in Docket No. 46831. The PUCT has the authority to require the Company to surcharge or refund such difference over a period not to exceed 18 months . The Company cannot predict the outcome or the timing of this rate case at this time. Energy Efficiency Cost Recovery Factor . On May 1, 2017, the Company filed its annual application, which was assigned PUCT Docket No. 47125, to establish its energy efficiency cost recovery factor for 2018. In addition to projected energy efficiency costs for 2018 and a true-up to prior year actual costs, the Company requested approval of a $1.0 million bonus for the 2016 energy efficiency program results in accordance with PUCT rules. A hearing on the merits of this case is scheduled to begin on August 15, 2017. The Company cannot predict the outcome of this matter at this time. Fuel and Purchased Power Costs. On November 30, 2016, the Company filed a request, which was assigned PUCT Docket No. 46610, to increase its fixed fuel factor by approximately 28.8% to reflect increased fuel expenses primarily related to an increase in the price of natural gas used to generate power. The increase in the fixed fuel factor was effective on an interim basis January 1, 2017 and approved by the PUCT on January 10, 2017. As of June 30, 2017 , the Company had under-recovered fuel costs in the amount of $8.5 million for the Texas jurisdiction. Fuel Reconciliation Proceeding . On September 27, 2016, the Company filed an application with the PUCT, designated as PUCT Docket No. 46308, to reconcile $436.6 million of Texas fuel and purchased power expenses incurred during the period of April 1, 2013 through March 31, 2016 . On June 29, 2017, the PUCT approved a settlement in this proceeding. The settlement provides for the reconciliation of fuel and purchased power costs incurred from April 1, 2013 through March 31, 2016 . Additionally, the settlement modifies and tightens the Palo Verde performance rewards measurement bands beginning with the 2018 performance period. The financial results for the three months ended June 30, 2017 include a $5.0 million , pre-tax increase to income reflecting the settlement of the Texas fuel reconciliation proceeding. This amount includes Palo Verde performance rewards associated with the 2013 to 2015 performance periods net of disallowed fuel and purchased power costs as approved in the settlement. As of June 30, 2017 , Texas jurisdictional fuel and purchased power costs subject to a future Texas fuel reconciliation are approximately $181.4 million . Community Solar. On June 8, 2015, the Company filed a petition with the PUCT to initiate a community solar program that includes the construction and ownership of a 3 MW solar photovoltaic system located at Montana Power Station. Participation will be on a voluntary basis, and customers will contract for a set capacity (kW) amount and receive all energy produced. This case was assigned PUCT Docket No. 44800. The Company filed a settlement agreement among all parties on July 1, 2016 approving the program, and the PUCT approved the settlement agreement and program on September 1, 2016. On April 19, 2017, the Company announced that the entire 3 MW program was fully subscribed by approximately 1,500 Texas customers. The Community Solar facility began commercial operation on May 31, 2017 . Four Corners Generating Station. On February 17, 2015 , the Company and Arizona Public Service Company ("APS") entered into an asset purchase agreement ("Purchase and Sale Agreement") providing for the sale of the Company's interest in Four Corners to APS. The sale of the Company's interest in Four Corners closed on July 6, 2016 . On June 10, 2015, the Company filed an application in Texas requesting reasonableness and public interest findings and certain rate and accounting findings related to the Purchase and Sale Agreement. This case was assigned PUCT Docket No. 44805. Subsequent to the filing of the application, the case has been subject to numerous procedural matters, including a March 23, 2016 order in which the PUCT determined not to dismiss the reasonableness and public interest issues in this docket but to consider the requested rate and accounting findings, including coal mine reclamation costs, in a rate case proceeding. On September 1, 2016, a motion by parties in the proceeding to suspend the procedural schedule in order to pursue settlement was approved. On March 3, 2017, the Company filed a Joint Motion to Implement Stipulation and Agreement ("Stipulation and Agreement"), and PUCT Staff filed its recommendation that the Company’s disposition of its interest in Four Corners was reasonable and consistent with the public interest. Additionally, the signatories of the Stipulation and Agreement agreed to support the recovery of the Company's Four Corners decommissioning costs in the ongoing Texas rate case. A final order approving the Stipulation and Agreement was adopted by the PUCT on March 30, 2017. Other Required Approvals . The Company has obtained other required approvals for tariffs and approvals required by the Public Utility Regulatory Act ("PURA") and the PUCT. New Mexico Regulatory Matters 2015 New Mexico Rate Case Filing . On May 11, 2015, the Company filed a request with the NMPRC, in Case No. 15-00127-UT, for an annual increase in non-fuel base rates. On June 8, 2016, the NMPRC issued its final order in Case No. 15-00127-UT ("NMPRC Final Order"), which approved an annual increase in non-fuel base rates of approximately $0.6 million , an increase of approximately $0.5 million in other service fees and a decrease in the Company's allowed return on equity to 9.48% . The NMPRC Final Order concluded that all of the Company's new plant in service was reasonable and necessary and therefore would be recoverable in rates. The Company's rates were approved by the NMPRC effective July 1, 2016 and implemented at such time. Future New Mexico Rate Case Filing. NMPRC Case No. 15-00109-UT required the Company to make a rate filing in New Mexico in the second quarter of 2017 using a historical test year ended December 31, 2016. On March 24, 2017, the Company, NMPRC Utility Division Staff and the New Mexico Attorney General filed a Joint Motion to Modify Filing Date Stated in Final Order requesting that the rate filing date be changed to no later than July 31, 2019, using the appropriate historical test year period. The joint request was approved by the NMPRC on April 12, 2017. Fuel and Purchased Power Costs. Historically, fuel and purchased power costs were recovered through base rates and a Fuel and Purchased Power Cost Adjustment Clause ("FPPCAC") that accounts for changes in the costs of fuel relative to the amount included in base rates. Effective July 1, 2016, with the implementation of the final order in Case No. 15-00127-UT, fuel and purchased power costs are no longer recovered through base rates but are recovered through the FPPCAC. The Company's request to reconcile its fuel and purchased power costs for the period January 1, 2013 through December 31, 2014 was approved in Case No. 15-00127-UT. New Mexico jurisdictional costs subject to prudence review are costs from January 1, 2015 through June 30, 2017 that total approximately $144.1 million . At June 30, 2017 , the Company had a net fuel over-recovery balance of approximately $0.3 million in New Mexico. 5 MW Holloman Air Force Base ("HAFB") Facility Certificate of Convenience and Necessity ("CCN") . On October 7, 2015, in NMPRC Case No. 15-00185-UT, the NMPRC issued a final order approving a CCN for a 5 MW solar power generation facility located on HAFB in the Company's service territory in New Mexico. The Company and HAFB negotiated a retail contract, which includes power sales agreement for the facility, to replace the existing load retention agreement which was approved by final order issued October 5, 2016 in NMPRC Case No. 16-00224-UT. Construction of the solar generation facility is expected to be completed in the first half of 2018. New Mexico Efficient Use of Energy Recovery Factor. On July 1, 2016 , the Company filed its annual application requesting approval of its 2017 Energy Efficiency and Load Management Plan and to establish energy efficiency cost recovery factors for 2017. In addition to projected energy efficiency costs for 2017, the Company requested approval of a $0.4 million incentive for 2017 energy efficiency programs in accordance with NMPRC rules. This case was assigned Case No. 16-00185-UT. On February 22, 2017 , the NMPRC issued a Final Order approving the Company’s 2017 Energy Efficiency and Load Management Plan and authorizing recovery in 2017 of a base incentive of $0.4 million . The Company’s energy efficiency cost recovery factors were approved and effective in customer bills beginning on March 1, 2017. On July 1, 2016 , the Company filed its 2015 Annual Report for Energy Efficiency Programs, which included an incentive for verified 2015 program performance of $0.3 million , which was approved in Case No. 13-00176-UT. The Company recorded the $0.3 million approved incentive in operating revenues in the first quarter of 2017. In addition, on June 30, 2017 , the Company filed its 2016 Annual Report for Energy Efficiency Programs, which included an incentive for verified 2016 program performance of $0.4 million which was approved in Case No. 13-00176-UT. Other Required Approvals . The Company has obtained other required approvals for other tariffs, securities transactions, recovery of energy efficiency costs through a base rate rider and other approvals as required by the NMPRC. Federal Regulatory Matters The Company has obtained required approvals for rates and tariffs, securities transactions and other approvals as required by the FERC.

Palo Verde

Palo Verde	6 Months Ended
	Jun. 30, 2017
Palo Verde [Abstract]
Palo Verde	Palo Verde Decommissioning . Pursuant to the Arizona Nuclear Power Project ("ANPP") Participation Agreement and federal law, the Company funds its share of the estimated costs to decommission Palo Verde Nuclear Generating Station ("Palo Verde") Units 1, 2 and 3, including the Common Facilities, through the term of their respective operating licenses and is required to maintain a minimum accumulation and funding level in its decommissioning account at the end of each annual reporting period during the life of the plant. The Company has established external trusts with an independent trustee, which enables the Company to record a current deduction for federal income tax purposes for most of the amounts funded. At June 30, 2017, the Company’s decommissioning trust fund had a balance of $271.3 million , which is above its minimum funding level. The Company monitors the status of its decommissioning funds and adjusts its deposits, if necessary. Decommissioning costs are estimated every three years based upon engineering cost studies performed by outside engineers retained by APS. In April 2017, the Palo Verde Participants approved the 2016 Palo Verde decommissioning study (“2016 Study”). The 2016 Study estimated that the Company must fund approximately $432.8 million (stated in 2016 dollars) to cover its share of decommissioning costs which was an increase in decommissioning costs of $52.1 million (stated in 2016 dollars) from the 2013 Palo Verde decommissioning study. The effect of this change increased the ARO by $3.5 million , which was recorded during the six months ended June 30, 2017, and will increase annual expenses starting in April 2017. Although the 2016 Study was based on the latest available information, there can be no assurance that decommissioning cost estimates will not increase in the future or that regulatory requirements will not change. In addition, until a new low-level radioactive waste repository opens and operates for a number of years, estimates of the cost to dispose of low-level radioactive waste are subject to uncertainty. As provided in the ANPP Participation Agreement, the participants are required to conduct a new decommissioning study every three years . While the Company attempts to seek amounts in rates to meet its decommissioning obligations, it is not able to conclude given the evidence available to it now that it is probable these costs will continue to be collected over the period until decommissioning begins in 2044. The Company is ultimately responsible for these costs and its future actions combined with future decisions from regulators will determine how successful the Company is in this effort. Spent Nuclear Fuel and Waste Disposal. Pursuant to the Nuclear Waste Policy Act of 1982, as amended in 1987 ("NWPA"), the U.S. Department of Energy ("DOE") is legally obligated to accept and dispose of all spent nuclear fuel and other high-level radioactive waste generated by all domestic power reactors by 1998. The DOE's obligations are reflected in a contract for Disposal of Spent Nuclear Fuel and/or High-Level Radioactive Waste ("Standard Contract") with each nuclear power plant. The DOE failed to begin accepting spent nuclear fuel by 1998. On October 31, 2014 , APS, acting on behalf of itself and the Palo Verde Participants, submitted to the government a request for reimbursement of spent nuclear fuel storage costs for the period July 1, 2011 through June 30, 2014 . The accepted claim amount was $42.0 million . On June 1, 2015 , the Company received approximately $6.6 million , representing its share of the award, of which $5.8 million was credited to customers through the applicable fuel adjustment clauses in March 2015. After June 2015, APS will file annual claims for the period July 1 of the then-previous year to June 30 of the then-current year. On November 2, 2015 , APS filed a $12.0 million claim for the period July 1, 2014 through June 30, 2015 . In February 2016, the DOE notified APS of the approval of the claim. In March 2016 , the Company received its share of this claim of approximately $1.9 million , of which $1.6 million was credited to customers through the applicable fuel adjustment clauses. On October 31, 2016 , APS filed an $11.3 million claim for the period July 1, 2015 through June 30, 2016 . On February 1, 2017, the DOE notified APS of the approval of the claim. On March 10, 2017 , the Company received approximately $1.8 million , representing its share of the award, of which $1.4 million was credited to customers through the applicable fuel adjustment clauses. Palo Verde Operations and Maintenance Expense . Included in other operations and maintenance expenses are expenses associated with Palo Verde as follows (in thousands): 2017 2016 Three months ended June 30, $ 25,931 $ 24,048 Six months ended June 30, 47,539 46,391 Twelve months ended June 30, 98,062 98,343

Common Stock

Common Stock	6 Months Ended
	Jun. 30, 2017
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shareholders' Equity and Share-based Payments, Including Earnings Per Share Information	Common Stock Dividends. The Company paid $13.6 million and $12.5 million in quarterly cash dividends during the three months ended June 30, 2017 and 2016 , respectively. The Company paid a total of $26.2 million and $51.3 million in quarterly cash dividends during the six and twelve months ended June 30, 2017 , respectively. The Company paid a total of $24.5 million and $48.4 million in quarterly cash dividends during the six and twelve months ended June 30, 2016 , respectively. On July 27, 2017 , the Board of Directors declared a quarterly cash dividend of $0.335 per share payable on September 29, 2017 to shareholders of record as of the close of business on September 15, 2017 . Basic and Diluted Earnings Per Share . The basic and diluted earnings per share are presented below (in thousands except for share data): Three Months Ended June 30, 2017 2016 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,409,030 40,345,150 Dilutive effect of unvested performance awards 116,555 54,341 Diluted number of common shares outstanding 40,525,585 40,399,491 Basic net income per common share: Net income $ 36,066 $ 22,284 Income allocated to participating restricted stock (142 ) (65 ) Net income available to common shareholders $ 35,924 $ 22,219 Diluted net income per common share: Net income $ 36,066 $ 22,284 Income reallocated to participating restricted stock (142 ) (65 ) Net income available to common shareholders $ 35,924 $ 22,219 Basic net income per common share: Distributed earnings $ 0.335 $ 0.31 Undistributed earnings 0.555 0.24 Basic net income per common share $ 0.890 $ 0.55 Diluted net income per common share: Distributed earnings $ 0.335 $ 0.31 Undistributed earnings 0.555 0.24 Diluted net income per common share $ 0.890 $ 0.55 Six Months Ended June 30, 2017 2016 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,398,192 40,335,236 Dilutive effect of unvested performance awards 101,152 45,404 Diluted number of common shares outstanding 40,499,344 40,380,640 Basic net income per common share: Net income $ 32,077 $ 16,476 Income allocated to participating restricted stock (119 ) (66 ) Net income available to common shareholders $ 31,958 $ 16,410 Diluted net income per common share: Net income $ 32,077 $ 16,476 Income reallocated to participating restricted stock (119 ) (66 ) Net income available to common shareholders $ 31,958 $ 16,410 Basic net income per common share: Distributed earnings $ 0.645 $ 0.605 Undistributed earnings 0.145 (0.195 ) Basic net income per common share $ 0.790 $ 0.410 Diluted net income per common share: Distributed earnings $ 0.645 $ 0.605 Undistributed earnings 0.145 (0.195 ) Diluted net income per common share $ 0.790 $ 0.410 Twelve Months Ended June 30, 2017 2016 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,381,776 40,314,032 Dilutive effect of unvested performance awards 85,219 42,207 Diluted number of common shares outstanding 40,466,995 40,356,239 Basic net income per common share: Net income $ 112,369 $ 73,864 Income allocated to participating restricted stock (423 ) (210 ) Net income available to common shareholders $ 111,946 $ 73,654 Diluted net income per common share: Net income $ 112,369 $ 73,864 Income reallocated to participating restricted stock (423 ) (210 ) Net income available to common shareholders $ 111,946 $ 73,654 Basic net income per common share: Distributed earnings $ 1.265 $ 1.195 Undistributed earnings 1.505 0.635 Basic net income per common share $ 2.770 $ 1.830 Diluted net income per common share: Distributed earnings $ 1.265 $ 1.195 Undistributed earnings 1.505 0.635 Diluted net income per common share $ 2.770 $ 1.830 The number of restricted stock awards and performance shares at 100% performance level excluded from the calculation of the diluted number of common shares outstanding because their effect was antidilutive is presented below: Three Months Ended Six months ended Twelve Months Ended June 30, June 30, June 30, 2017 2016 2017 2016 2017 2016 Restricted stock awards 58,792 42,759 68,409 51,111 62,352 52,714 Performance shares (a) — 62,995 — 62,995 6,906 56,089 (a) Certain performance shares were excluded from the computation of diluted earnings per share as no payouts would have been required based upon performance at the end of each corresponding period.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2017
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
Income Taxes	Income Taxes The Company files income tax returns in the United States ("U.S.") federal jurisdiction and in the states of Texas, New Mexico and Arizona. The Company is no longer subject to tax examination by the taxing authorities in the federal, Arizona and New Mexico jurisdictions for years prior to 2012 . The Company is currently under audit in Texas for tax years 2007 through 2010 . For the three months ended June 30, 2017 and 2016 , the Company’s effective tax rate was 35.4% and 33.9% , respectively. For the six months ended June 30, 2017 and 2016, the Company's effective tax rate was 35.3% and 33.5% , respectively. For the twelve months ended June 30, 2017 and 2016 , the Company's effective tax rate was 36.0% and 30.7% , respectively. The Company's effective tax rate for all periods differs from the federal statutory tax rate of 35.0% primarily due to capital gains in the decommissioning trusts which are taxed at the federal rate of 20.0% , the allowance for equity funds used during construction ("AEFUDC"), state taxes and the issue discussed in the following paragraph. In the third quarter of 2016, the Company changed its accounting for state income taxes from the flow-through method to the normalization method in accordance with the PUCT's and NMPRC's most recent final orders. Under the flow-through method, the Company previously recorded deferred state income taxes and regulatory liabilities and assets offsetting such deferred state income taxes at the expected cash flow to be reflected in future rates. Upon implementation of normalization, the Company began amortizing the net regulatory asset for deferred state income taxes to deferred income tax expense over a 15 year period as allowed by the regulators. In the third quarter of 2016, the Company began recording deferred state income tax expense as required by normalization, retroactive to January 2016 as provided in the final orders. The impact of the change was additional deferred income tax expense of $1.1 million , $ 1.7 million and $ 4.9 million for the three, six and twelve months ended June 30, 2017 , respectively.

Commitments, Contingencies And

Commitments, Contingencies And Uncertainties	6 Months Ended
	Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments, Contingencies And Uncertainties	Commitments, Contingencies and Uncertainties For a full discussion of commitments and contingencies, see Note K of the Notes to Financial Statements in the 2016 Form 10-K. In addition, see Notes C and D above and Notes C and E of the Notes to Financial Statements in the 2016 Form 10-K regarding matters related to wholesale power sales contracts and transmission contracts subject to regulation and Palo Verde, including decommissioning, spent nuclear fuel and waste disposal, and liability and insurance matters. Power Purchase and Sale Contracts To supplement its own generation and operating reserve requirements, and to meet required renewable portfolio standards, the Company engages in power purchase arrangements which may vary in duration and amount based on an evaluation of the Company's resource needs, the economics of the transactions, and specific renewable portfolio requirements. For a full discussion of power purchase and sale contracts that the Company has entered into with various counterparties, see Note K of the Notes to Financial Statements in the 2016 Form 10-K. The Company is exploring the possibility of a purchase of Renewable Energy Certificates to comply with New Mexico Renewable Portfolio Standard(s) requirements and the NMPRC's approval to complete such a purchase is pending. Environmental Matters General. The Company is subject to extensive laws, regulations and permit requirements with respect to air and greenhouse gas ("GHG") emissions, water discharges, soil and water quality, waste management and disposal, natural resources and other environmental matters by federal, state, regional, tribal and local authorities. Failure to comply with such laws, regulations and requirements can result in actions by authorities or other third parties that might seek to impose on the Company administrative, civil and/or criminal penalties or other sanctions. In addition, releases of pollutants or contaminants into the environment can result in costly cleanup liabilities. These laws, regulations and requirements are subject to change through modification or reinterpretation, or the introduction of new laws and regulations and, as a result, the Company may face additional capital and operating costs to comply. On March 28, 2017 the Company entered into a Compliance Agreement (“Compliance Agreement”) with the Texas Commission on Environmental Quality under the Texas Environmental, Health and Safety Audit Privilege Act to address certain water and waste compliance issues associated with the integrity of the synthetic liner of the evaporation pond at the Company’s Newman Generating Station. The Company's action plan was initiated in the second quarter of 2017 and will continue to be implemented over the three year period of the Compliance Agreement. The Company is currently evaluating the cost of performing its obligations under the Compliance Agreement.

Litigation

Litigation	6 Months Ended
	Jun. 30, 2017
Litigation [Abstract]
Litigation Matters Disclosure	Litigation The Company is involved in various legal, environmental, tax and regulatory proceedings before various courts, regulatory commissions and governmental agencies regarding matters arising in the ordinary course of business. In many of these matters, the Company has excess casualty liability insurance that covers the various claims, actions and complaints. The Company regularly analyzes current information and, as necessary, makes provisions in its financial statements for probable liabilities for the eventual disposition of these matters. While the outcome of these matters cannot be predicted with certainty, based upon a review of the matters and applicable insurance coverage, the Company believes that none of these matters will have a material adverse effect on the financial position, results of operations or cash flows of the Company. The Company expenses legal costs, including expenses related to loss contingencies, as they are incurred. See Notes C and G above and Notes C and K of the Notes to Financial Statements in the 2016 Form 10-K for discussion of the effects of government legislation and regulation on the Company.

Employee Benefits

Employee Benefits	6 Months Ended
	Jun. 30, 2017
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Employee Benefits	Employee Benefits Retirement Plans The net periodic benefit cost recognized for the three, six and twelve months ended June 30, 2017 and 2016 is made up of the components listed below as determined using the projected unit credit actuarial cost method (in thousands): Three Months Ended Six Months Ended Twelve Months Ended June 30, June 30, June 30, 2017 2016 2017 2016 2017 2016 Components of net periodic benefit cost: Service cost $ 1,989 $ 1,905 $ 4,259 $ 3,810 $ 8,450 $ 8,402 Interest cost 3,282 3,265 6,530 6,530 13,039 13,775 Expected return on plan assets (4,787 ) (4,713 ) (9,595 ) (9,425 ) (19,049 ) (19,325 ) Amortization of: Net loss 2,138 1,887 4,227 3,775 7,791 8,922 Prior service benefit (875 ) (877 ) (1,753 ) (1,755 ) (3,504 ) (3,486 ) Net periodic benefit cost $ 1,747 $ 1,467 $ 3,668 $ 2,935 $ 6,727 $ 8,288 During the six months ended June 30, 2017 , the Company contributed $6.5 million of its projected $10.0 million 2017 annual contribution to its retirement plans. Other Postretirement Benefits The net periodic benefit recognized for the three, six and twelve months ended June 30, 2017 and 2016 is made up of the components listed below (in thousands): Three Months Ended Six Months Ended Twelve Months Ended June 30, June 30, June 30, 2017 2016 2017 2016 2017 2016 Components of net periodic benefit: Service cost $ 530 $ 715 $ 1,118 $ 1,430 $ 2,457 $ 3,134 Interest cost 684 872 1,362 1,745 2,784 3,730 Expected return on plan assets (483 ) (460 ) (953 ) (920 ) (1,868 ) (1,940 ) Amortization of: Prior service benefit (1,538 ) (787 ) (3,076 ) (1,575 ) (5,402 ) (3,093 ) Net gain (444 ) (665 ) (839 ) (1,330 ) (1,883 ) (2,355 ) Net periodic benefit $ (1,251 ) $ (325 ) $ (2,388 ) $ (650 ) $ (3,912 ) $ (524 ) During the six months ended June 30, 2017 , the Company contributed $0.2 million of its projected $2.4 million 2017 annual contribution to its other postretirement benefits plan.

Financial Instruments And Inves

Financial Instruments And Investments (Notes)	6 Months Ended
	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Financial Instruments and Investments	Financial Instruments and Investments The FASB guidance requires the Company to disclose estimated fair values for its financial instruments. The Company has determined that cash and temporary investments, investment in debt securities, accounts receivable, decommissioning trust funds, long-term debt, short-term borrowings under the Revolving Credit Facility ("RCF"), accounts payable and customer deposits meet the definition of financial instruments. The carrying amounts of cash and temporary investments, accounts receivable, accounts payable and customer deposits approximate fair value because of the short maturity of these items. Investments in debt securities and decommissioning trust funds are carried at estimated fair value. Long-Term Debt and Short-Term Borrowings Under the RCF. The fair values of the Company's long-term debt and short-term borrowings under the RCF are based on estimated market prices for similar issues and are presented below (in thousands): June 30, 2017 December 31, 2016 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Pollution Control Bonds $ 190,913 $ 204,498 $ 190,775 $ 206,818 Senior Notes 993,254 1,173,767 993,086 1,112,285 RGRT Senior Notes (1) 94,849 98,075 94,795 98,855 RCF (1) 178,884 178,884 81,574 81,574 Total $ 1,457,900 $ 1,655,224 $ 1,360,230 $ 1,499,532 _______________ (1) Nuclear fuel financing, as of June 30, 2017 and December 31, 2016 , is funded through the $95 million Rio Grande Resources Trust ("RGRT") Senior Notes and $38.9 million and $37.6 million , respectively under the RCF. As of June 30, 2017 , $140.0 million was outstanding under the RCF for working capital or general corporate purposes. As of December 31, 2016 , $44.0 million was outstanding under the RCF for working capital or general corporate purposes. The interest rate on the Company's borrowings under the RCF is reset throughout the quarter reflecting c urrent market rates. Consequently, the carrying value approximates fair value. Marketable Securities. The Company's marketable securities, included in decommissioning trus t funds in the Balance Sheets, are reported at fair value which was $271.3 million and $255.7 million at June 30, 2017 and December 31, 2016 , respectively. These securities are classified as available for sale and recorded at their estimated fair value using the FASB guidance for certain investments in debt and equity securities. The reported fair values include gross unrealized losses on marketable securities whose impairment the Company has deemed to be temporary. The tables below present the gross unrealized losses and the fair value of these securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position (in thousands): June 30, 2017 Less than 12 Months 12 Months or Longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Description of Securities (1) : Federal Agency Mortgage Backed Securities $ 15,446 $ (188 ) $ 415 $ (19 ) $ 15,861 $ (207 ) U.S. Government Bonds 35,388 (598 ) 9,816 (630 ) 45,204 (1,228 ) Municipal Debt Obligations 6,903 (165 ) 5,928 (482 ) 12,831 (647 ) Corporate Debt Obligations 7,308 (79 ) 2,944 (235 ) 10,252 (314 ) Total Debt Securities 65,045 (1,030 ) 19,103 (1,366 ) 84,148 (2,396 ) Common Stock 718 (65 ) — — 718 (65 ) Total Temporarily Impaired Securities $ 65,763 $ (1,095 ) $ 19,103 $ (1,366 ) $ 84,866 $ (2,461 ) _________________ (1) Includes 136 securities. December 31, 2016 Less than 12 Months 12 Months or Longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Description of Securities (2) : Federal Agency Mortgage Backed Securities $ 11,582 $ (239 ) $ 436 $ (22 ) $ 12,018 $ (261 ) U.S. Government Bonds 31,655 (762 ) 17,976 (835 ) 49,631 (1,597 ) Municipal Debt Obligations 9,596 (394 ) 4,067 (372 ) 13,663 (766 ) Corporate Debt Obligations 7,971 (172 ) 2,092 (172 ) 10,063 (344 ) Total Debt Securities 60,804 (1,567 ) 24,571 (1,401 ) 85,375 (2,968 ) Common Stock 2,760 (167 ) — — 2,760 (167 ) Institutional Equity Funds-International Equity 22,945 (110 ) — — 22,945 (110 ) Total Temporarily Impaired Securities $ 86,509 $ (1,844 ) $ 24,571 $ (1,401 ) $ 111,080 $ (3,245 ) _________________ (2) Includes 152 securities. The Company monitors the length of time specific securities trade below their cost basis along with the amount and percentage of the unrealized loss in determining if a decline in fair value of marketable securities below recorded cost is considered to be other than temporary. The Company recognizes impairment losses on certain of its securities deemed to be other than temporary. In accordance with the FASB guidance, these impairment losses are recognized in net income, and a lower cost basis is established for these securities. In addition, the Company will research the future prospects of individual securities as necessary. The Company does not anticipate expending monies held in trust before 2044 or a later period when decommissioning of Palo Verde begins. For the three, six and twelve months ended June 30, 2017 and 2016 , the Company recognized other than temporary impairment losses on its available-for-sale securities as follow (in thousands): Three Months Ended Six Months Ended Twelve Months Ended June 30, June 30, June 30, 2017 2016 2017 2016 2017 2016 Unrealized holding losses included in pre-tax income $ — $ — $ — $ (156 ) $ (196 ) $ (494 ) The reported securities also include gross unrealized gains on marketable securities which have not been recognized in the Company's net income. The table below presents the unrecognized gross unrealized gains and the fair value of these securities, aggregated by investment category (in thousands): June 30, 2017 December 31, 2016 Fair Value Unrealized Gains Fair Value Unrealized Gains Description of Securities: Federal Agency Mortgage Backed Securities $ 6,662 $ 272 $ 7,430 $ 319 U.S. Government Bonds 13,846 311 12,237 138 Municipal Debt Obligations 5,197 161 2,481 144 Corporate Debt Obligations 20,981 995 12,350 655 Total Debt Securities 46,686 1,739 34,498 1,256 Common Stock 53,489 30,766 61,884 34,066 Equity Mutual Funds 54,236 7,028 42,244 3,345 Institutional Funds - International Equity 26,149 3,174 — — Cash and Cash Equivalents 5,889 — 6,002 — Total $ 186,449 $ 42,707 $ 144,628 $ 38,667 The Company's marketable securities include investments in mortgage backed securities, municipal, corporate and federal debt obligations. The contractual year for maturity of these available-for-sale securities as of June 30, 2017 is as follows (in thousands): Total 2017 2018 2022 through 2026 2027 and Beyond Federal Agency Mortgage Backed Securities $ 22,523 $ — $ 5 $ 338 $ 22,180 U.S. Government Bonds 59,050 5,893 24,224 15,981 12,952 Municipal Debt Obligations 18,028 796 6,215 9,743 1,274 Corporate Debt Obligations 31,233 — 12,309 8,949 9,975 The Company's marketable securities in its decommissioning trust funds are sold from time to time and the Company uses the specific identification basis to determine the amount to reclassify from accumulated other comprehensive income into net income. The proceeds from the sale of these securities during the three, six and twelve months ended June 30, 2017 and 2016 and the related effects on pre-tax income are as follows (in thousands): Three Months Ended Six Months Ended Twelve Months Ended June 30, June 30, June 30, 2017 2016 2017 2016 2017 2016 Proceeds from sales or maturities of available-for-sale securities $ 36,476 $ 16,634 $ 62,531 $ 40,712 $ 113,087 $ 106,121 Gross realized gains included in pre-tax income $ 5,322 $ 2,409 $ 7,909 $ 4,241 $ 12,880 $ 12,805 Gross realized losses included in pre-tax income (156 ) (299 ) (552 ) (587 ) (1,185 ) (1,262 ) Gross unrealized losses included in pre-tax income — — — (156 ) (196 ) (494 ) Net gains included in pre-tax income $ 5,166 $ 2,110 $ 7,357 $ 3,498 $ 11,499 $ 11,049 Net unrealized holding gains (losses) included in accumulated other comprehensive income $ 4,458 $ 2,790 $ 12,179 $ 4,980 $ 15,643 $ 2,623 Net gains reclassified from accumulated other comprehensive income (5,166 ) (2,110 ) (7,357 ) (3,498 ) (11,499 ) (11,049 ) Net gains (losses) in other comprehensive income $ (708 ) $ 680 $ 4,822 $ 1,482 $ 4,144 $ (8,426 ) Fair Value Measurements. The FASB guidance requires the Company to provide expanded quantitative disclosures for financial assets and liabilities recorded on the balance sheet at fair value. Financial assets carried at fair value include the Company's decommissioning trust investments and investments in debt securities which are included in deferred charges and other assets on the Balance Sheets. The Company has no liabilities that are measured at fair value on a recurring basis. The FASB guidance establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three levels as follows: • Level 1 – Observable inputs that reflect quoted market prices for identical assets and liabilities in active markets. Financial assets utilizing Level 1 inputs include the nuclear decommissioning trust investments in active exchange-traded equity securities, mutual funds and U.S. Treasury securities that are in a highly liquid and active market. The Institutional Funds are valued using the Net Asset Value ("NAV") provided by the administrator of the fund. The NAV price is quoted on a restrictive market although the underlying investments are traded on active markets. During the third quarter of 2016, the Company concluded that the NAV used for determining the fair value of the Institutional Funds-International Equity investments have readily determinable fair values. Accordingly, such fund values have been re-categorized from Level 2 to Level 1 hierarchy. • Level 2 – Inputs other than quoted market prices included in Level 1 that are observable for the asset or liability either directly or indirectly. Financial assets utilizing Level 2 inputs include the nuclear decommissioning trust investments in fixed income securities. The fair value of these financial instruments is based on evaluated prices that reflect observable market information, such as actual trade information of similar securities, adjusted for observable differences. • Level 3 – Unobservable inputs using data that is not corroborated by market data and primarily based on internal Company analysis using models and various other analysis. Financial assets utilizing Level 3 inputs are the Company's investment in debt securities. The securities in the Company's decommissioning trust funds are valued using prices and other relevant information generated by market transactions involving identical or comparable securities. The FASB guidance identifies this valuation technique as the "market approach" with observable inputs. The Company analyzes available-for-sale securities to determine if losses are other than temporary. The fair value of the Company's decommissioning trust funds and investments in debt securities at June 30, 2017 and December 31, 2016 , and the level within the three levels of the fair value hierarchy defined by the FASB guidance are presented in the table below (in thousands): Description of Securities Fair Value as of June 30, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Trading Securities: Investments in Debt Securities $ 1,538 $ — $ — $ 1,538 Available for Sale: Federal Agency Mortgage Backed Securities $ 22,523 $ — $ 22,523 $ — U.S. Government Bonds 59,050 59,050 — — Municipal Debt Obligations 18,028 — 18,028 — Corporate Debt Obligations 31,233 — 31,233 — Subtotal, Debt Securities 130,834 59,050 71,784 — Common Stock 54,207 54,207 — — Equity Mutual Funds 54,236 54,236 — — Institutional Funds-International Equity 26,149 26,149 — — Cash and Cash Equivalents 5,889 5,889 — — Total Available for Sale $ 271,315 $ 199,531 $ 71,784 $ — Description of Securities Fair Value as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Trading Securities: Investments in Debt Securities $ 1,421 $ — $ — $ 1,421 Available for Sale: Federal Agency Mortgage Backed Securities $ 19,448 $ — $ 19,448 $ — U.S. Government Bonds 61,868 61,868 — — Municipal Debt Obligations 16,144 — 16,144 — Corporate Debt Obligations 22,413 — 22,413 — Subtotal, Debt Securities 119,873 61,868 58,005 — Common Stock 64,644 64,644 — — Equity Mutual Funds 42,244 42,244 — — Institutional Funds-International Equity 22,945 22,945 — — Cash and Cash Equivalents 6,002 6,002 — — Total Available for Sale $ 255,708 $ 197,703 $ 58,005 $ — There were no transfers in or out of Level 1 and Level 2 fair value measurements categories due to changes in observable inputs during the three, six and twelve month periods ended June 30, 2017 and 2016 . There were no purchases, sales, issuances, and settlements related to the assets in the Level 3 fair value measurement category during the three, six and twelve months ended June 30, 2017 and 2016 .

Principles Of Preparation (Poli

Principles Of Preparation (Policy)	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Use of Estimates, Policy	Use of Estimates . The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. The Company evaluates its estimates on an on-going basis, including those related to depreciation, unbilled revenue, income taxes, fuel costs, pension and other post-retirement obligations and asset retirement obligations ("ARO"). Actual results could differ from those estimates.
Revenue Recognition, Policy	Revenues . Revenues related to the sale of electricity are generally recorded when service is provided or electricity is delivered to customers. The billing of electricity sales to retail customers is based on the reading of their meters, which occurs on a systematic basis throughout the month. Unbilled revenues are recorded for estimated amounts of energy delivered in the period following the customer's billing cycle to the end of the month. Unbilled revenues are estimated based on monthly generation volumes and by applying an average revenue/kWh to the number of estimated kWhs delivered but not billed. Accounts receivable included accrued unbilled revenues of $36.1 million at June 30, 2017 and $21.0 million at December 31, 2016 . The Company presents revenues net of sales taxes in its statements of operations.
Depreciation, Depletion, and Amortization, Policy	Depreciation. The Company routinely evaluates the depreciable service lives, cost of removal and salvage values of its property, plant and equipment. Depreciation is provided on a straight-line basis over the estimated remaining lives of the assets (ranging in average from 5 to 48 years). When property subject to composite depreciation is retired or otherwise disposed of in the normal course of business, its cost, together with the cost of removal, less salvage, is charged to accumulated depreciation. For other property dispositions, the applicable cost and accumulated depreciation is removed from the balance sheet accounts and a gain or loss is recognized.
New Accounting Standards, Policy	New Accounting Standards In March 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2016-09, Compensation - Stock Compensation (Topic 718) Improvements to Employee Share-Based Payment Accounting to simplify the accounting for share-based payment transactions, including the income tax consequences, classification of awards either as equity or liabilities, and classification on the statements of cash flows. The Company adopted the new standard effective January 1, 2017. The adoption of the new standard did not have a material impact on the Company’s financial condition, results of operations or cash flows. The cumulative effect of the adoption of the new standard was to increase net operating loss carryforward deferred tax assets and retained earnings by $0.2 million on January 1, 2017. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) to provide a framework that replaces the existing revenue recognition guidance, and has since modified the standard with several ASUs. The standard provides that an entity should recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. More specifically, the standard requires entities to recognize revenue through the application of a five-step model, which includes the: (i) identification of the contract; (ii) identification of the performance obligations; (iii) determination of the transaction price; (iv) allocation of the transaction price to the performance obligations; and (v) the recognition of revenue as the entity satisfies the performance obligations. The Company plans to adopt the new standard for reporting periods beginning after December 15, 2017. The Company currently anticipates using the modified retrospective approach. The Company is currently in the process of evaluating the impact of the new standard on its various revenue and cash flow streams, including the evaluation of the impact, if any, on changes to business processes, systems and controls to support recognition and disclosure under the new guidance. Tariff sales to customers are determined to be in the scope of the new standard and represent a significant portion of the Company’s total operating revenues. The Company currently expects that the timing or pattern of revenue recognition from tariff sales will not significantly change. The Company's evaluation of other revenue streams is ongoing. The Company's initial assessments may change as it executes its implementation plan and new guidance is provided by the American Institute of Certified Public Accountants Power and Utilities Industry Task Force. The completion of these assessments could impact current accounting policies, revenue recognition and disclosures in the notes to the financial statements. In January 2016, the FASB issued ASU 2016-01, Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Liabilities to enhance the reporting model for financial instruments by addressing certain aspects of recognition, measurement, presentation, and disclosure. ASU 2016-01 generally requires entities to measure equity investments that do not result in consolidation and are not accounted for under the equity method at fair value and recognize any changes in fair value in net income. The guidance for classifying and measuring investments in debt securities and loans is not changed by this ASU, but requires entities to record changes in other comprehensive income. Financial assets and financial liabilities must be separately presented by measurement category on the balance sheet or in the accompanying notes to the financial statements. ASU 2016-01 clarifies the need for a valuation allowance on a deferred tax asset related to available-for-sale securities in combination with the entity's other deferred tax assets. The provisions of this ASU become effective for reporting periods beginning after December 15, 2017. Upon adoption of the new standard, the Company expects to record the cumulative effects as of January 1, 2018 which will result in an adjustment to accumulated other comprehensive income (losses) and retained earnings for unrealized gains (losses) related to equity securities owned by the Company. The Company is continuing to assess the future impact of this ASU. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) to increase transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and requiring qualitative and quantitative disclosures on leasing agreements. ASU 2016-02 maintains a distinction between finance leases and operating leases similar to the distinction under previous leases guidance for capital leases and operating leases. The impact of leases reported in the Company's operating results and statement of cash flows are expected to be similar to previous GAAP. ASU 2016-02 requires the recognition in the statement of financial position, by the lessee, of a liability to make lease payments (lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term. How leases are recorded in regard to financial position represents a significant change from previous GAAP guidance. The lessee is permitted to make an accounting policy election to not recognize lease assets and lease liabilities for short-term leases. Implementation of the standard will be required for reporting periods beginning after December 15, 2018. Adoption of the new lease accounting standard will require the Company to apply the new standard to the earliest period using a modified retrospective approach. The Company is currently in the process of evaluating the impact of the new standard, including the evaluation of the impact, if any, on changes to business processes, systems and controls to support recognition and disclosure under the new guidance, however, at this time is unable to determine the impact this standard will have on the financial statements and related disclosures. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326). ASU 2016-13 changes how companies measure and recognize credit impairment for many financial assets. The new current expected credit loss model will require companies to immediately recognize an estimate of credit losses expected to occur over the remaining life of the financial assets that are in the scope of the standard. The ASU also makes targeted amendments to the current impairment model for available-for-sale debt securities. The provisions in ASU 2016-13 will be required for reporting periods beginning after December 15, 2019. ASU 2016-13 will be applied in a modified-retrospective approach through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is implemented. The Company is currently assessing the future impact of ASU 2016-13. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230) Classification of Certain Cash Receipts and Cash Payments to reduce diversity in practice in how certain cash receipts and cash payments are classified in the statement of cash flows. The provisions in ASU 2016-15 will be required for reporting periods beginning after December 15, 2017. ASU 2016-15 will be applied using a retrospective transition method to each period presented. If it is impracticable to apply ASU 2016-15 retrospectively for some of the issues, the amendments for those issues may be applied prospectively as of the earliest date practicable. The Company is currently assessing the future impact of this ASU. In March 2017, the FASB issued ASU 2017-07, Compensation-Retirement Benefits (Topic 715) Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. ASU 2017-07 amends Accounting Standards Codification 715, Compensation - Retirement Benefits, to require companies to present the service cost component of net benefit cost in the income statement line items where compensation cost is reported. Companies will present all other components of net benefit cost separately from the line item(s) that includes the service cost and outside of any subtotal of operating income. In addition, only the service cost component will be eligible for capitalization in assets. The amendments in ASU 2017-07 will be required for reporting periods beginning after December 15, 2017. The amendments in ASU 2017-07 should be applied retrospectively for the income statement presentation of the service cost component and the other components of net benefit costs and prospectively, on and after the effective date, for the capitalization of the service cost component. The Company is currently assessing the future impact of this ASU. In May 2017, the FASB issued ASU 2017-09, Compensation-Stock Compensation (Topic 718), Scope of Modification Accounting, to provide guidance about when to account for a change to the terms or conditions of a share-based payment award as a modification. Under ASU 2017-09, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award (as equity or liability) changes as a result of the change in terms or conditions. The amendments of ASU 2017-09 will be required for reporting periods beginning after December 15, 2017. ASU 2017-09 should be applied prospectively to an award modified on or after the adoption date. The Company is assessing the future impact of ASU 2017-09; however, it currently does not expect the impact of this ASU to be significant.

Principles Of Preparation (Tabl

Principles Of Preparation (Tables)	6 Months Ended
	Jun. 30, 2017
Supplemental Cash Flow Information [Abstract]
Cash Flow, Supplemental Disclosures	Supplemental Cash Flow Disclosures (in thousands) Six Months Ended June 30, 2017 2016 Cash paid (received) for: Interest on long-term debt and borrowings under the revolving credit facility $ 35,304 $ 35,252 Income tax paid, net 2,251 2,703 Non-cash investing and financing activities: Changes in accrued plant additions (9,105 ) (6,966 ) Plant additions to be reimbursed by insurance 3,525 — Grants of restricted shares of common stock 1,171 1,236 Issuance of performance shares 932 —

Accumulated Other Comprehensi20

Accumulated Other Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Schedule of Accumulated Other Comprehensive Income (Loss)	Changes in Accumulated Other Comprehensive Income (Loss) (net of tax) by component are presented below (in thousands): Three Months Ended June 30, 2017 Three Months Ended June 30, 2016 Unrecognized Pension and Post-retirement Benefit Costs Net Unrealized Gains (Losses) on Marketable Securities Net Losses on Cash Flow Hedges Accumulated Other Comprehensive Income (Loss) Unrecognized Pension and Post-retirement Benefit Costs Net Unrealized Gains (Losses) on Marketable Securities Net Losses on Cash Flow Hedges Accumulated Other Comprehensive Income (Loss) Balance at beginning of period $ (24,457 ) $ 32,872 $ (11,599 ) $ (3,184 ) $ (30,256 ) $ 28,394 $ (11,770 ) $ (13,632 ) Other comprehensive income before reclassifications — 3,558 — 3,558 — 2,224 — 2,224 Amounts reclassified from accumulated other comprehensive income (loss) (458 ) (4,134 ) 85 (4,507 ) (276 ) (1,693 ) 77 (1,892 ) Balance at end of period $ (24,915 ) $ 32,296 $ (11,514 ) $ (4,133 ) $ (30,532 ) $ 28,925 $ (11,693 ) $ (13,300 ) Six Months Ended June 30, 2017 Six Months Ended June 30, 2016 Unrecognized Pension and Post-retirement Benefit Costs Net Unrealized Gains (Losses) on Marketable Securities Net Losses on Cash Flow Hedges Accumulated Other Comprehensive Income (Loss) Unrecognized Pension and Post-retirement Benefit Costs Net Unrealized Gains (Losses) on Marketable Securities Net Losses on Cash Flow Hedges Accumulated Other Comprehensive Income (Loss) Balance at beginning of period $ (23,928 ) $ 28,463 $ (11,651 ) $ (7,116 ) $ (29,869 ) $ 27,765 $ (11,810 ) $ (13,914 ) Other comprehensive income before reclassifications — 9,723 — 9,723 — 3,966 — 3,966 Amounts reclassified from accumulated other comprehensive income (loss) (987 ) (5,890 ) 137 (6,740 ) (663 ) (2,806 ) 117 (3,352 ) Balance at end of period $ (24,915 ) $ 32,296 $ (11,514 ) $ (4,133 ) $ (30,532 ) $ 28,925 $ (11,693 ) $ (13,300 ) Twelve Months Ended June 30, 2017 Twelve Months Ended June 30, 2016 Unrecognized Pension and Post-retirement Benefit Costs Net Unrealized Gains (Losses) on Marketable Securities Net Losses on Cash Flow Hedges Accumulated Other Comprehensive Income (Loss) Unrecognized Pension and Post-retirement Benefit Costs Net Unrealized Gains (Losses) on Marketable Securities Net Losses on Cash Flow Hedges Accumulated Other Comprehensive Income (Loss) Balance at beginning of period $ (30,532 ) $ 28,925 $ (11,693 ) $ (13,300 ) $ (34,331 ) $ 35,726 $ (11,959 ) $ (10,564 ) Other comprehensive income before reclassifications 7,363 12,661 — 20,024 3,777 2,080 — 5,857 Amounts reclassified from accumulated other comprehensive income (loss) (1,746 ) (9,290 ) 179 (10,857 ) 22 (8,881 ) 266 (8,593 ) Balance at end of period $ (24,915 ) $ 32,296 $ (11,514 ) $ (4,133 ) $ (30,532 ) $ 28,925 $ (11,693 ) $ (13,300 )
Reclassification out of Accumulated Other Comprehensive Income	Amounts reclassified from Accumulated Other Comprehensive Income (Loss) for the three, six and twelve months ended June 30, 2017 and 2016 are as follows (in thousands): Details about Accumulated Other Comprehensive Income (Loss) Components Three Months Ended June 30, Six Months Ended June 30, Twelve Months Ended June 30, Affected Line Item in the Statement of Operations 2017 2016 2017 2016 2017 2016 Amortization of pension and post-retirement benefit costs: Prior service benefit $ 2,413 $ 1,664 $ 4,829 $ 3,330 $ 8,906 $ 6,579 (a) Net loss (1,694 ) (1,222 ) (3,388 ) (2,445 ) (5,908 ) (6,567 ) (a) 719 442 1,441 885 2,998 12 (a) Income tax effect (261 ) (166 ) (454 ) (222 ) (1,252 ) (34 ) Income tax benefit 458 276 987 663 1,746 (22 ) Net income (loss) Marketable securities: Net realized gain on sale of securities 5,166 2,110 7,357 3,498 11,499 11,049 Investment and interest income, net 5,166 2,110 7,357 3,498 11,499 11,049 Income before income taxes Income tax effect (1,032 ) (417 ) (1,467 ) (692 ) (2,209 ) (2,168 ) Income tax benefit 4,134 1,693 5,890 2,806 9,290 8,881 Net income Loss on cash flow hedge: Amortization of loss (132 ) (123 ) (262 ) (245 ) (515 ) (482 ) Interest on long-term debt and revolving credit facility (132 ) (123 ) (262 ) (245 ) (515 ) (482 ) Loss before income taxes Income tax effect 47 46 125 128 336 216 Income tax expense (85 ) (77 ) (137 ) (117 ) (179 ) (266 ) Net loss Total reclassifications $ 4,507 $ 1,892 $ 6,740 $ 3,352 $ 10,857 $ 8,593 (a) These items are included in the computation of net periodic benefit cost. See Note I, Employee Benefits, for additional information.

Palo Verde (Tables)

Palo Verde (Tables)	6 Months Ended
	Jun. 30, 2017
Palo Verde Generating Station
Palo Verde Operations & Maintenance Expenses [Line Items]
Operations & Maintenance Expenses	Palo Verde Operations and Maintenance Expense . Included in other operations and maintenance expenses are expenses associated with Palo Verde as follows (in thousands): 2017 2016 Three months ended June 30, $ 25,931 $ 24,048 Six months ended June 30, 47,539 46,391 Twelve months ended June 30, 98,062 98,343

Common Stock (Tables)

Common Stock (Tables)	6 Months Ended
	Jun. 30, 2017
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	Basic and Diluted Earnings Per Share . The basic and diluted earnings per share are presented below (in thousands except for share data): Three Months Ended June 30, 2017 2016 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,409,030 40,345,150 Dilutive effect of unvested performance awards 116,555 54,341 Diluted number of common shares outstanding 40,525,585 40,399,491 Basic net income per common share: Net income $ 36,066 $ 22,284 Income allocated to participating restricted stock (142 ) (65 ) Net income available to common shareholders $ 35,924 $ 22,219 Diluted net income per common share: Net income $ 36,066 $ 22,284 Income reallocated to participating restricted stock (142 ) (65 ) Net income available to common shareholders $ 35,924 $ 22,219 Basic net income per common share: Distributed earnings $ 0.335 $ 0.31 Undistributed earnings 0.555 0.24 Basic net income per common share $ 0.890 $ 0.55 Diluted net income per common share: Distributed earnings $ 0.335 $ 0.31 Undistributed earnings 0.555 0.24 Diluted net income per common share $ 0.890 $ 0.55 Six Months Ended June 30, 2017 2016 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,398,192 40,335,236 Dilutive effect of unvested performance awards 101,152 45,404 Diluted number of common shares outstanding 40,499,344 40,380,640 Basic net income per common share: Net income $ 32,077 $ 16,476 Income allocated to participating restricted stock (119 ) (66 ) Net income available to common shareholders $ 31,958 $ 16,410 Diluted net income per common share: Net income $ 32,077 $ 16,476 Income reallocated to participating restricted stock (119 ) (66 ) Net income available to common shareholders $ 31,958 $ 16,410 Basic net income per common share: Distributed earnings $ 0.645 $ 0.605 Undistributed earnings 0.145 (0.195 ) Basic net income per common share $ 0.790 $ 0.410 Diluted net income per common share: Distributed earnings $ 0.645 $ 0.605 Undistributed earnings 0.145 (0.195 ) Diluted net income per common share $ 0.790 $ 0.410 Twelve Months Ended June 30, 2017 2016 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,381,776 40,314,032 Dilutive effect of unvested performance awards 85,219 42,207 Diluted number of common shares outstanding 40,466,995 40,356,239 Basic net income per common share: Net income $ 112,369 $ 73,864 Income allocated to participating restricted stock (423 ) (210 ) Net income available to common shareholders $ 111,946 $ 73,654 Diluted net income per common share: Net income $ 112,369 $ 73,864 Income reallocated to participating restricted stock (423 ) (210 ) Net income available to common shareholders $ 111,946 $ 73,654 Basic net income per common share: Distributed earnings $ 1.265 $ 1.195 Undistributed earnings 1.505 0.635 Basic net income per common share $ 2.770 $ 1.830 Diluted net income per common share: Distributed earnings $ 1.265 $ 1.195 Undistributed earnings 1.505 0.635 Diluted net income per common share $ 2.770 $ 1.830
Schedule of Antidilutive Securities Excluded From Computation Of Earnings Per Share	The number of restricted stock awards and performance shares at 100% performance level excluded from the calculation of the diluted number of common shares outstanding because their effect was antidilutive is presented below: Three Months Ended Six months ended Twelve Months Ended June 30, June 30, June 30, 2017 2016 2017 2016 2017 2016 Restricted stock awards 58,792 42,759 68,409 51,111 62,352 52,714 Performance shares (a) — 62,995 — 62,995 6,906 56,089 (a) Certain performance shares were excluded from the computation of diluted earnings per share as no payouts would have been required based upon performance at the end of each corresponding period.

Employee Benefits (Tables)

Employee Benefits (Tables)	6 Months Ended
	Jun. 30, 2017
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Schedule of Net Benefit Costs	The net periodic benefit cost recognized for the three, six and twelve months ended June 30, 2017 and 2016 is made up of the components listed below as determined using the projected unit credit actuarial cost method (in thousands): Three Months Ended Six Months Ended Twelve Months Ended June 30, June 30, June 30, 2017 2016 2017 2016 2017 2016 Components of net periodic benefit cost: Service cost $ 1,989 $ 1,905 $ 4,259 $ 3,810 $ 8,450 $ 8,402 Interest cost 3,282 3,265 6,530 6,530 13,039 13,775 Expected return on plan assets (4,787 ) (4,713 ) (9,595 ) (9,425 ) (19,049 ) (19,325 ) Amortization of: Net loss 2,138 1,887 4,227 3,775 7,791 8,922 Prior service benefit (875 ) (877 ) (1,753 ) (1,755 ) (3,504 ) (3,486 ) Net periodic benefit cost $ 1,747 $ 1,467 $ 3,668 $ 2,935 $ 6,727 $ 8,288
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Schedule of Net Benefit Costs	The net periodic benefit recognized for the three, six and twelve months ended June 30, 2017 and 2016 is made up of the components listed below (in thousands): Three Months Ended Six Months Ended Twelve Months Ended June 30, June 30, June 30, 2017 2016 2017 2016 2017 2016 Components of net periodic benefit: Service cost $ 530 $ 715 $ 1,118 $ 1,430 $ 2,457 $ 3,134 Interest cost 684 872 1,362 1,745 2,784 3,730 Expected return on plan assets (483 ) (460 ) (953 ) (920 ) (1,868 ) (1,940 ) Amortization of: Prior service benefit (1,538 ) (787 ) (3,076 ) (1,575 ) (5,402 ) (3,093 ) Net gain (444 ) (665 ) (839 ) (1,330 ) (1,883 ) (2,355 ) Net periodic benefit $ (1,251 ) $ (325 ) $ (2,388 ) $ (650 ) $ (3,912 ) $ (524 )

Financial Instruments And Inv24

Financial Instruments And Investments (Tables)	6 Months Ended
	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Fair Values Of Long-Term Debt And Short-Term Borrowings Under the RCF	The fair values of the Company's long-term debt and short-term borrowings under the RCF are based on estimated market prices for similar issues and are presented below (in thousands): June 30, 2017 December 31, 2016 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Pollution Control Bonds $ 190,913 $ 204,498 $ 190,775 $ 206,818 Senior Notes 993,254 1,173,767 993,086 1,112,285 RGRT Senior Notes (1) 94,849 98,075 94,795 98,855 RCF (1) 178,884 178,884 81,574 81,574 Total $ 1,457,900 $ 1,655,224 $ 1,360,230 $ 1,499,532 _______________ (1) Nuclear fuel financing, as of June 30, 2017 and December 31, 2016 , is funded through the $95 million Rio Grande Resources Trust ("RGRT") Senior Notes and $38.9 million and $37.6 million , respectively under the RCF. As of June 30, 2017 , $140.0 million was outstanding under the RCF for working capital or general corporate purposes. As of December 31, 2016 , $44.0 million was outstanding under the RCF for working capital or general corporate purposes. The interest rate on the Company's borrowings under the RCF is reset throughout the quarter reflecting c urrent market rates. Consequently, the carrying value approximates fair value.
Unrecognized Gross Unrealized Gains (Losses) And the Fair Value	The tables below present the gross unrealized losses and the fair value of these securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position (in thousands): June 30, 2017 Less than 12 Months 12 Months or Longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Description of Securities (1) : Federal Agency Mortgage Backed Securities $ 15,446 $ (188 ) $ 415 $ (19 ) $ 15,861 $ (207 ) U.S. Government Bonds 35,388 (598 ) 9,816 (630 ) 45,204 (1,228 ) Municipal Debt Obligations 6,903 (165 ) 5,928 (482 ) 12,831 (647 ) Corporate Debt Obligations 7,308 (79 ) 2,944 (235 ) 10,252 (314 ) Total Debt Securities 65,045 (1,030 ) 19,103 (1,366 ) 84,148 (2,396 ) Common Stock 718 (65 ) — — 718 (65 ) Total Temporarily Impaired Securities $ 65,763 $ (1,095 ) $ 19,103 $ (1,366 ) $ 84,866 $ (2,461 ) _________________ (1) Includes 136 securities. December 31, 2016 Less than 12 Months 12 Months or Longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Description of Securities (2) : Federal Agency Mortgage Backed Securities $ 11,582 $ (239 ) $ 436 $ (22 ) $ 12,018 $ (261 ) U.S. Government Bonds 31,655 (762 ) 17,976 (835 ) 49,631 (1,597 ) Municipal Debt Obligations 9,596 (394 ) 4,067 (372 ) 13,663 (766 ) Corporate Debt Obligations 7,971 (172 ) 2,092 (172 ) 10,063 (344 ) Total Debt Securities 60,804 (1,567 ) 24,571 (1,401 ) 85,375 (2,968 ) Common Stock 2,760 (167 ) — — 2,760 (167 ) Institutional Equity Funds-International Equity 22,945 (110 ) — — 22,945 (110 ) Total Temporarily Impaired Securities $ 86,509 $ (1,844 ) $ 24,571 $ (1,401 ) $ 111,080 $ (3,245 ) _________________ (2) Includes 152 securities.
Unrealized Holding Losses Included In Pre-Tax Income	For the three, six and twelve months ended June 30, 2017 and 2016 , the Company recognized other than temporary impairment losses on its available-for-sale securities as follow (in thousands): Three Months Ended Six Months Ended Twelve Months Ended June 30, June 30, June 30, 2017 2016 2017 2016 2017 2016 Unrealized holding losses included in pre-tax income $ — $ — $ — $ (156 ) $ (196 ) $ (494 )
Marketable Securities Fair Value and Unrecognized Gross Unrealized Gain	The table below presents the unrecognized gross unrealized gains and the fair value of these securities, aggregated by investment category (in thousands): June 30, 2017 December 31, 2016 Fair Value Unrealized Gains Fair Value Unrealized Gains Description of Securities: Federal Agency Mortgage Backed Securities $ 6,662 $ 272 $ 7,430 $ 319 U.S. Government Bonds 13,846 311 12,237 138 Municipal Debt Obligations 5,197 161 2,481 144 Corporate Debt Obligations 20,981 995 12,350 655 Total Debt Securities 46,686 1,739 34,498 1,256 Common Stock 53,489 30,766 61,884 34,066 Equity Mutual Funds 54,236 7,028 42,244 3,345 Institutional Funds - International Equity 26,149 3,174 — — Cash and Cash Equivalents 5,889 — 6,002 — Total $ 186,449 $ 42,707 $ 144,628 $ 38,667
Contractual Year For Maturity Of Available-For-Sale Securities	The contractual year for maturity of these available-for-sale securities as of June 30, 2017 is as follows (in thousands): Total 2017 2018 2022 through 2026 2027 and Beyond Federal Agency Mortgage Backed Securities $ 22,523 $ — $ 5 $ 338 $ 22,180 U.S. Government Bonds 59,050 5,893 24,224 15,981 12,952 Municipal Debt Obligations 18,028 796 6,215 9,743 1,274 Corporate Debt Obligations 31,233 — 12,309 8,949 9,975
Sale of Securities And The Related Effects On Pre-Tax Income	The proceeds from the sale of these securities during the three, six and twelve months ended June 30, 2017 and 2016 and the related effects on pre-tax income are as follows (in thousands): Three Months Ended Six Months Ended Twelve Months Ended June 30, June 30, June 30, 2017 2016 2017 2016 2017 2016 Proceeds from sales or maturities of available-for-sale securities $ 36,476 $ 16,634 $ 62,531 $ 40,712 $ 113,087 $ 106,121 Gross realized gains included in pre-tax income $ 5,322 $ 2,409 $ 7,909 $ 4,241 $ 12,880 $ 12,805 Gross realized losses included in pre-tax income (156 ) (299 ) (552 ) (587 ) (1,185 ) (1,262 ) Gross unrealized losses included in pre-tax income — — — (156 ) (196 ) (494 ) Net gains included in pre-tax income $ 5,166 $ 2,110 $ 7,357 $ 3,498 $ 11,499 $ 11,049 Net unrealized holding gains (losses) included in accumulated other comprehensive income $ 4,458 $ 2,790 $ 12,179 $ 4,980 $ 15,643 $ 2,623 Net gains reclassified from accumulated other comprehensive income (5,166 ) (2,110 ) (7,357 ) (3,498 ) (11,499 ) (11,049 ) Net gains (losses) in other comprehensive income $ (708 ) $ 680 $ 4,822 $ 1,482 $ 4,144 $ (8,426 )
Fair Value, Measurement Inputs, Disclosure	The fair value of the Company's decommissioning trust funds and investments in debt securities at June 30, 2017 and December 31, 2016 , and the level within the three levels of the fair value hierarchy defined by the FASB guidance are presented in the table below (in thousands): Description of Securities Fair Value as of June 30, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Trading Securities: Investments in Debt Securities $ 1,538 $ — $ — $ 1,538 Available for Sale: Federal Agency Mortgage Backed Securities $ 22,523 $ — $ 22,523 $ — U.S. Government Bonds 59,050 59,050 — — Municipal Debt Obligations 18,028 — 18,028 — Corporate Debt Obligations 31,233 — 31,233 — Subtotal, Debt Securities 130,834 59,050 71,784 — Common Stock 54,207 54,207 — — Equity Mutual Funds 54,236 54,236 — — Institutional Funds-International Equity 26,149 26,149 — — Cash and Cash Equivalents 5,889 5,889 — — Total Available for Sale $ 271,315 $ 199,531 $ 71,784 $ — Description of Securities Fair Value as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Trading Securities: Investments in Debt Securities $ 1,421 $ — $ — $ 1,421 Available for Sale: Federal Agency Mortgage Backed Securities $ 19,448 $ — $ 19,448 $ — U.S. Government Bonds 61,868 61,868 — — Municipal Debt Obligations 16,144 — 16,144 — Corporate Debt Obligations 22,413 — 22,413 — Subtotal, Debt Securities 119,873 61,868 58,005 — Common Stock 64,644 64,644 — — Equity Mutual Funds 42,244 42,244 — — Institutional Funds-International Equity 22,945 22,945 — — Cash and Cash Equivalents 6,002 6,002 — — Total Available for Sale $ 255,708 $ 197,703 $ 58,005 $ —

Principles Of Preparation (Accr

Principles Of Preparation (Accrued Unbilled Revenues) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Accrued unbilled revenues	$ 36.1	$ 21

Principles Of Preparation (Supp

Principles Of Preparation (Supplemental Cash Flow Disclosures) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Supplemental Cash Flow Information [Abstract]
Interest on long-term debt and borrowings under the revolving credit facility	$ 35,304	$ 35,252
Income tax paid, net	2,251	2,703
Changes in accrued plant additions	(9,105)	(6,966)
Plant additions to be reimbursed by insurance	3,525	0
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued	1,171	1,236
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued	$ 932	$ 0

Principles Of Preparation (Depr

Principles Of Preparation (Depreciation) (Details)	6 Months Ended
	Jun. 30, 2017
Minimum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Maximum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	48 years

Principles Of Preparation Narra

Principles Of Preparation Narrative (Details) $ in Millions	Jan. 01, 2017USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in operating loss carryforward deferred tax assets	$ 0.2
Increase in retained earnings	$ 0.2

Accumulated Other Comprehensi29

Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance				$ (7,116)
Accumulated Other Comprehensive Income (Loss), ending balance		$ (4,133)		(4,133)		$ (4,133)
Accumulated Defined Benefit Plans Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance		(24,457)	$ (30,256)	(23,928)	$ (29,869)	(30,532)	$ (34,331)
Other Comprehensive Income (Loss) before Reclassifications		0	0	0	0	7,363	3,777
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	[1]	(458)	(276)	(987)	(663)	(1,746)	22
Accumulated Other Comprehensive Income (Loss), ending balance		(24,915)	(30,532)	(24,915)	(30,532)	(24,915)	(30,532)
Accumulated Net Unrealized Investment Gain (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance		32,872	28,394	28,463	27,765	28,925	35,726
Other Comprehensive Income (Loss) before Reclassifications		3,558	2,224	9,723	3,966	12,661	2,080
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)		(4,134)	(1,693)	(5,890)	(2,806)	(9,290)	(8,881)
Accumulated Other Comprehensive Income (Loss), ending balance		32,296	28,925	32,296	28,925	32,296	28,925
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance		(11,599)	(11,770)	(11,651)	(11,810)	(11,693)	(11,959)
Other Comprehensive Income (Loss) before Reclassifications		0	0	0	0	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)		85	77	137	117	179	266
Accumulated Other Comprehensive Income (Loss), ending balance		(11,514)	(11,693)	(11,514)	(11,693)	(11,514)	(11,693)
Accumulated Other Comprehensive Income (Loss), Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance		(3,184)	(13,632)	(7,116)	(13,914)	(13,300)	(10,564)
Other Comprehensive Income (Loss) before Reclassifications		3,558	2,224	9,723	3,966	20,024	5,857
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)		(4,507)	(1,892)	(6,740)	(3,352)	(10,857)	(8,593)
Accumulated Other Comprehensive Income (Loss), ending balance		$ (4,133)	$ (13,300)	$ (4,133)	$ (13,300)	$ (4,133)	$ (13,300)
[1]	These items are included in the computation of net periodic benefit cost. See Note I, Employee Benefits, for additional information.

Accumulated Other Comprehensi30

Accumulated Other Comprehensive Income Amounts Reclassified (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income (loss) before income taxes		$ 55,846	$ 33,734	$ 49,569	$ 24,765	$ 175,490	$ 106,559
Income tax expense (benefit)		(19,780)	(11,450)	(17,492)	(8,289)	(63,121)	(32,695)
Net income (loss)		36,066	22,284	32,077	16,476	112,369	73,864
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]	2,413	1,664	4,829	3,330	8,906	6,579
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]	(1,694)	(1,222)	(3,388)	(2,445)	(5,908)	(6,567)
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]	719	442	1,441	885	2,998	12
Reclassification from AOCI, Current Period, Tax		(261)	(166)	(454)	(222)	(1,252)	(34)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	458	276	987	663	1,746	(22)
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		4,134	1,693	5,890	2,806	9,290	8,881
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(85)	(77)	(137)	(117)	(179)	(266)
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		4,507	1,892	6,740	3,352	10,857	8,593
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized gain on sale of securities		5,166	2,110	7,357	3,498	11,499	11,049
Income (loss) before income taxes		5,166	2,110	7,357	3,498	11,499	11,049
Income tax expense (benefit)		(1,032)	(417)	(1,467)	(692)	(2,209)	(2,168)
Net income (loss)		4,134	1,693	5,890	2,806	9,290	8,881
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income (loss) before income taxes		(132)	(123)	(262)	(245)	(515)	(482)
Income tax expense (benefit)		47	46	125	128	336	216
Net income (loss)		(85)	(77)	(137)	(117)	(179)	(266)
Interest Rate Contract | Reclassification out of Accumulated Other Comprehensive Income | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest on long-term debt and revolving credit facility		$ (132)	$ (123)	$ (262)	$ (245)	$ (515)	$ (482)
[1]	These items are included in the computation of net periodic benefit cost. See Note I, Employee Benefits, for additional information.

Regulation (Narrative) (Details

Regulation (Narrative) (Details) $ in Thousands

Jul. 21, 2017USD ($)

Jun. 29, 2017

May 01, 2017USD ($)

Feb. 22, 2017USD ($)

Feb. 13, 2017USD ($)

Jan. 10, 2017

Sep. 27, 2016USD ($)

Aug. 25, 2016USD ($)

Jul. 01, 2016USD ($)

Jun. 08, 2016USD ($)

Jun. 30, 2017USD ($)

Mar. 31, 2017USD ($)

Jun. 30, 2017USD ($)MW

Dec. 31, 2016USD ($)

Under-collection of fuel revenues

$ 8,515

$ 8,515

$ 11,123

Over-collection of fuel revenues

314

$ 314

$ 255

PUCT

Period To Relate Back New Rates

155 days

Under-collection of fuel revenues

$ 8,500

$ 8,500

Reconcilable Fuel Expense

$ 181,400

PUCT | Four Corners Generating Station

Purchase and Sale Agreement, Execution Date

Feb. 17, 2015

PUCT | Community Solar At Montana Power Station

Electric Capacity | MW

3

Number of customers subscribed

1,500

1,500

Property, Plant and Equipment, Operational Date

May 31, 2017

PUCT | Maximum

Surcharge Or Refund Period

18 months

PUCT | Four Corners Generating Station

Closing Date of Sale

Jul. 6, 2016

PUCT | Subsequent Event

Public Utilities, Requested Rate Increase (Decrease), Amended Decrease Amount

$ 3,000

NMPRC

Reconcilable Fuel Expense

$ 144,100

Fuel Reconciliation Period

30 months

Over-collection of fuel revenues

$ 300

$ 300

NMPRC | Holloman

Electric Capacity | MW

5

Non-Fuel Base Rate | PUCT

Public Utilities, Requested Rate Increase, Amount

$ 42,500

Non-Fuel Base Rate | PUCT | Subsequent Event

Public Utilities, Requested Rate Increase, Amended Amount

$ 39,200

2016 Energy Efficiency Programs | PUCT

Public Utilities Requested Performance Incentive Bonus Related To Energy Efficiency Program

$ 1,000

2016 Energy Efficiency Programs | NMPRC

Public Utilities Requested Performance Incentive Bonus Related To Energy Efficiency Program

400

2017 Energy Efficiency Programs | NMPRC

Public Utilities Requested Performance Incentive Bonus Related To Energy Efficiency Program

$ 400

Public Utilities Approved Performance Incentive Bonus Related To Energy Efficiency Program

$ 400

2015 Energy Efficiency Programs | NMPRC

Public Utilities Requested Performance Incentive Bonus Related To Energy Efficiency Program

$ 300

Public Utilities Approved Performance Incentive Bonus Related To Energy Efficiency Program

$ 300

Public Utilities, Regulatory Rate Making Impact | PUCT

Recovery of rate case expenses

$ 3,100

Period To Relate Back New Rates

80 days

Public Utilities, Regulatory Rate Making Impact | NMPRC

Public Utilities, Approved Return on Equity, Percentage

9.48%

Public Utilities, Regulatory Rate Making Impact | Non-Fuel Base Rate | PUCT | Four Corners Generating Station

Public Utilities, Approved Rate Increase, Amount

$ 3,700

Regulatory Current Asset, End Date for Recovery

Jul. 11, 2017

Public Utilities, Regulatory Rate Making Impact | Non-Fuel Base Rate | NMPRC

Public Utilities, Approved Rate Increase, Amount

$ 600

Public Utilities, Regulatory Rate Making Impact | Utility Cost Of Service | NMPRC

Public Utilities, Approved Rate Increase, Amount

$ 500

PUCT Docket No. 46610 | Fixed Fuel Factor

Increase In Fixed Fuel Factor, Percentage

28.80%

PUCT Docket No. 46308

Reconcilable Fuel Expense

$ 436,600

Fuel Reconciliation Period

36 months

36 months

Fuel reconciliation effect, net amount

$ 5,000

NMPRC Case No. 15-00127-UT

Fuel Reconciliation Period

24 months

Palo Verde (Narrative) (Detail

Palo Verde (Narrative) (Details) - USD ($) $ in Thousands	Mar. 10, 2017	Oct. 31, 2016	Mar. 31, 2016	Nov. 02, 2015	Jun. 01, 2015	Oct. 31, 2014	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Jointly Owned Utility Plant Interests [Line Items]
Decommissioning Fund Investments							$ 271,315		$ 255,708
Third Party Decommission Cost Estimates Study Period, in Years							3 years
Required period in years participants need a new decommissioning study							3 years
Refund passed through to customers							$ 2,667	$ (1,990)
Palo Verde Generating Station
Jointly Owned Utility Plant Interests [Line Items]
Decommissioning Fund Investments							271,300
Estimated Decommissioning Costs							432,800
Decommission Cost Increase							52,100
Asset Retirement Obligation, Revision of Estimate Increase							$ 3,500
Suit Against Department of Energy for Spent Fuel
Jointly Owned Utility Plant Interests [Line Items]
Settlement Agreement, Counterparty's Name							U.S. Department of Energy
Lawsuit Filing Date		Oct. 31, 2016		Nov. 2, 2015		Oct. 31, 2014
Suit Against Department of Energy for Spent Fuel | Palo Verde Generating Station
Jointly Owned Utility Plant Interests [Line Items]
Settlement, Amount	$ 1,800		$ 1,900		$ 6,600
Refund passed through to customers	$ 1,400		$ 1,600		$ 5,800
Settlement Agreement Award Received, Date	Mar. 10, 2017		Mar. 31, 2016		Jun. 1, 2015
Suit Against Department of Energy for Spent Fuel | Palo Verde Participants
Jointly Owned Utility Plant Interests [Line Items]
Settlement, Amount		$ 11,300		$ 12,000		$ 42,000
Minimum | Suit Against Department of Energy for Spent Fuel
Jointly Owned Utility Plant Interests [Line Items]
Litigation, Period Covered		Jul. 1, 2015		Jul. 1, 2014		Jul. 1, 2011
Maximum | Suit Against Department of Energy for Spent Fuel
Jointly Owned Utility Plant Interests [Line Items]
Litigation, Period Covered		Jun. 30, 2016		Jun. 30, 2015		Jun. 30, 2014

Palo Verde Operations and Maint

Palo Verde Operations and Maintenance Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Palo Verde Generating Station
Operations & Maintenance Expenses [Line Items]
Utilities Operating Expense, Maintenance and Operations	$ 25,931	$ 24,048	$ 47,539	$ 46,391	$ 98,062	$ 98,343

Common Stock (Narrative) (Detai

Common Stock (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 29, 2017	Sep. 15, 2017	Jul. 27, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Dividends, Common Stock, Cash				$ 13,600	$ 12,500	$ 26,157	$ 24,474	$ 51,300	$ 48,400
Common Stock, Dividends, Per Share, Declared				$ 0.335	$ 0.310	$ 0.645	$ 0.605	$ 1.265	$ 1.195
Scenario, Forecast
Dividends Payable, Date to be Paid	Sep. 29, 2017
Dividends Payable, Date of Record		Sep. 15, 2017
Subsequent Event
Dividends Payable, Date Declared			Jul. 27, 2017
Common Stock, Dividends, Per Share, Declared			$ 0.335

Common Stock (Basic And Diluted

Common Stock (Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Basic number of common shares outstanding	40,409,030	40,345,150	40,398,192	40,335,236	40,381,776	40,314,032
Dilutive effect of unvested performance awards	116,555	54,341	101,152	45,404	85,219	42,207
Diluted number of common shares outstanding	40,525,585	40,399,491	40,499,344	40,380,640	40,466,995	40,356,239
Net income	$ 36,066	$ 22,284	$ 32,077	$ 16,476	$ 112,369	$ 73,864
Income allocated to participating restricted stock	(142)	(65)	(119)	(66)	(423)	(210)
Net income available to common shareholders, basic	35,924	22,219	31,958	16,410	111,946	73,654
Income reallocated to participating restricted stock	(142)	(65)	(119)	(66)	(423)	(210)
Net income available to common shareholders, diluted	$ 35,924	$ 22,219	$ 31,958	$ 16,410	$ 111,946	$ 73,654
Earnings Per Share, Basic, Distributed	$ 0.335	$ 0.310	$ 0.645	$ 0.605	$ 1.265	$ 1.195
Earnings (losses) Per Share, Basic, Undistributed	0.555	0.240	0.145	(0.195)	1.505	0.635
Basic net income per common share	0.890	0.550	0.790	0.410	2.770	1.830
Earnings Per Share, Diluted, Distributed	0.335	0.310	0.645	0.605	1.265	1.195
Earnings (losses) Per Share, Diluted, Undistributed	0.555	0.240	0.145	(0.195)	1.505	0.635
Diluted net income per common share	$ 0.890	$ 0.550	$ 0.790	$ 0.410	$ 2.770	$ 1.830

Common Stock (Antidilutive Secu

Common Stock (Antidilutive Securities Excluded From Computation Of Earnings Per Share) (Details) - shares		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Performance shares payout based upon performance		0	0	0	0	0	0
Performance shares payout level		100.00%	100.00%	100.00%	100.00%	100.00%	100.00%
Restricted Stock
Antidilutive Securities Excluded from the Computation of Diluted Earnings Per Share, Amount		58,792	42,759	68,409	51,111	62,352	52,714
Performance Shares
Antidilutive Securities Excluded from the Computation of Diluted Earnings Per Share, Amount	[1]	0	62,995	0	62,995	6,906	56,089
[1]	Certain performance shares were excluded from the computation of diluted earnings per share as no payouts would have been required based upon performance at the end of each corresponding period.

Income Taxes (Income Tax Rates)

Income Taxes (Income Tax Rates) (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Tax [Line Items]
Effective tax rate	35.40%	33.90%	35.30%	33.50%	36.00%	30.70%
Federal statutory tax rate	35.00%	35.00%	35.00%	35.00%	35.00%	35.00%
Income Tax Rate Capital Gains	20.00%	20.00%	20.00%	20.00%	20.00%	20.00%

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017
Income Tax [Line Items]
Deferred Income Tax Expense		$ 15,339	$ 6,695
Internal Revenue Service (IRS) | Latest Tax Year
Income Tax [Line Items]
Tax Year Closed		2,011
NEW MEXICO | Latest Tax Year
Income Tax [Line Items]
Tax Year Closed		2,011
TEXAS | Earliest Tax Year
Income Tax [Line Items]
Income Tax Examination, Year under Examination		2,007
TEXAS | Latest Tax Year
Income Tax [Line Items]
Income Tax Examination, Year under Examination		2,010
ARIZONA | Latest Tax Year
Income Tax [Line Items]
Tax Year Closed		2,011
Change in Accounting Method Accounted for as Change in Estimate
Income Tax [Line Items]
Regulatory Asset, Amortization Period		15 years
Deferred Income Tax Expense	$ 1,100	$ 1,700		$ 4,900

Commitments, Contingencies An39

Commitments, Contingencies And Uncertainties (Narrative) (Details)	Mar. 28, 2017
Commitments and Contingencies Disclosure [Abstract]
Action Plan Implementation Period	3 years

Employee Benefits (Retirement P

Employee Benefits (Retirement Plans And Other Postretirement Benefits) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,989	$ 1,905	$ 4,259	$ 3,810	$ 8,450	$ 8,402
Interest cost	3,282	3,265	6,530	6,530	13,039	13,775
Expected return on plan assets	(4,787)	(4,713)	(9,595)	(9,425)	(19,049)	(19,325)
Amortization of net (gain) loss	2,138	1,887	4,227	3,775	7,791	8,922
Amortization of prior service benefit	(875)	(877)	(1,753)	(1,755)	(3,504)	(3,486)
Net periodic benefit cost (benefit)	1,747	1,467	3,668	2,935	6,727	8,288
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	530	715	1,118	1,430	2,457	3,134
Interest cost	684	872	1,362	1,745	2,784	3,730
Expected return on plan assets	(483)	(460)	(953)	(920)	(1,868)	(1,940)
Amortization of net (gain) loss	(444)	(665)	(839)	(1,330)	(1,883)	(2,355)
Amortization of prior service benefit	(1,538)	(787)	(3,076)	(1,575)	(5,402)	(3,093)
Net periodic benefit cost (benefit)	$ (1,251)	$ (325)	$ (2,388)	$ (650)	$ (3,912)	$ (524)

Employee Benefits (Narrative) (

Employee Benefits (Narrative) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017USD ($)
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Employer Contribution	$ 6.5
Defined Benefit Plan, Expected Contributions in Current Fiscal Year	10
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Employer Contribution	0.2
Defined Benefit Plan, Expected Contributions in Current Fiscal Year	$ 2.4

Financial Instruments And Inv42

Financial Instruments And Investments (Carrying Amount and Fair Value Amounts) (Details) - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Carrying (Reported) Amount, Fair Value Disclosure
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		$ 1,457,900	$ 1,360,230
Carrying (Reported) Amount, Fair Value Disclosure | Pollution Control Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		190,913	190,775
Carrying (Reported) Amount, Fair Value Disclosure | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		993,254	993,086
Carrying (Reported) Amount, Fair Value Disclosure | RGRT Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[1]	94,849	94,795
Carrying (Reported) Amount, Fair Value Disclosure | Revolving Credit Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[1]	178,884	81,574
Estimate of Fair Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		1,655,224	1,499,532
Estimate of Fair Value Measurement | Pollution Control Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		204,498	206,818
Estimate of Fair Value Measurement | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		1,173,767	1,112,285
Estimate of Fair Value Measurement | RGRT Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[1]	98,075	98,855
Estimate of Fair Value Measurement | Revolving Credit Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[1]	$ 178,884	$ 81,574
[1]	Nuclear fuel financing, as of June 30, 2017 and December 31, 2016, is funded through the $95 million Rio Grande Resources Trust ("RGRT") Senior Notes and $38.9 million and $37.6 million, respectively under the RCF. As of June 30, 2017, $140.0 million was outstanding under the RCF for working capital or general corporate purposes. As of December 31, 2016, $44.0 million was outstanding under the RCF for working capital or general corporate purposes. The interest rate on the Company's borrowings under the RCF is reset throughout the quarter reflecting current market rates. Consequently, the carrying value approximates fair value.

Financial Instruments And Inv43

Financial Instruments And Investments (Long-Term Debt and Short-Term Borrowings - Narratives) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financial Instruments and Investments [Line Items]
Decommissioning Fund Investments	$ 271,315	$ 255,708
Nuclear Fuel Financing
Financial Instruments and Investments [Line Items]
Line of Credit Facility, Amount Outstanding	38,900	37,600
Working Capital and General Purpose
Financial Instruments and Investments [Line Items]
Line of Credit Facility, Amount Outstanding	140,000	44,000
RGRT Senior Notes
Financial Instruments and Investments [Line Items]
Long-term Debt, Gross	$ 95,000	$ 95,000

Financial Instruments And Inv44

Financial Instruments And Investments (Marketable Securities Fair Value And Unrealized Losses) (Details) $ in Thousands		6 Months Ended		12 Months Ended
		Jun. 30, 2017USD ($)securities		Dec. 31, 2016USD ($)securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		$ 65,763	[1]	$ 86,509	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(1,095)	[1]	(1,844)	[2]
Marketable Securities Fair Value 12 Months or Longer		19,103	[1]	24,571	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(1,366)	[1]	(1,401)	[2]
Marketable Securities Fair Value Total		84,866	[1]	111,080	[2]
Marketable Securities Unrealized Losses Total		$ (2,461)	[1]	$ (3,245)	[2]
Number of securities | securities		136		152
Debt Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		$ 65,045	[1]	$ 60,804	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(1,030)	[1]	(1,567)	[2]
Marketable Securities Fair Value 12 Months or Longer		19,103	[1]	24,571	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(1,366)	[1]	(1,401)	[2]
Marketable Securities Fair Value Total		84,148	[1]	85,375	[2]
Marketable Securities Unrealized Losses Total		(2,396)	[1]	(2,968)	[2]
Federal Agency Mortgage Backed Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		15,446	[1]	11,582	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(188)	[1]	(239)	[2]
Marketable Securities Fair Value 12 Months or Longer		415	[1]	436	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(19)	[1]	(22)	[2]
Marketable Securities Fair Value Total		15,861	[1]	12,018	[2]
Marketable Securities Unrealized Losses Total		(207)	[1]	(261)	[2]
U.S. Government Bonds
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		35,388	[1]	31,655	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(598)	[1]	(762)	[2]
Marketable Securities Fair Value 12 Months or Longer		9,816	[1]	17,976	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(630)	[1]	(835)	[2]
Marketable Securities Fair Value Total		45,204	[1]	49,631	[2]
Marketable Securities Unrealized Losses Total		(1,228)	[1]	(1,597)	[2]
Municipal Obligations
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		6,903	[1]	9,596	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(165)	[1]	(394)	[2]
Marketable Securities Fair Value 12 Months or Longer		5,928	[1]	4,067	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(482)	[1]	(372)	[2]
Marketable Securities Fair Value Total		12,831	[1]	13,663	[2]
Marketable Securities Unrealized Losses Total		(647)	[1]	(766)	[2]
Corporate Obligations
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		7,308	[1]	7,971	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(79)	[1]	(172)	[2]
Marketable Securities Fair Value 12 Months or Longer		2,944	[1]	2,092	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(235)	[1]	(172)	[2]
Marketable Securities Fair Value Total		10,252	[1]	10,063	[2]
Marketable Securities Unrealized Losses Total		(314)	[1]	(344)	[2]
Common Stock
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		718	[1]	2,760	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(65)	[1]	(167)	[2]
Marketable Securities Fair Value 12 Months or Longer		0	[1]	0	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		0	[1]	0	[2]
Marketable Securities Fair Value Total		718	[1]	2,760	[2]
Marketable Securities Unrealized Losses Total		$ (65)	[1]	(167)	[2]
Institutional Funds-International Equity
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months	[2]			22,945
Marketable Securities Unrealized Losses Less Than 12 Months	[2]			(110)
Marketable Securities Fair Value 12 Months or Longer	[2]			0
Marketable Securities Unrealized Losses 12 Months or Longer	[2]			0
Marketable Securities Fair Value Total	[2]			22,945
Marketable Securities Unrealized Losses Total	[2]			$ (110)
[1]	Includes 136 securities.
[2]	Includes 152 securities.

Financial Instruments And Inv45

Financial Instruments And Investments (Unrealized Holding Losses Included In Pre-Tax Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financial Instruments And Investments [Abstract]
Unrealized losses included in pre-tax income	$ 0	$ 0	$ 0	$ (156)	$ (196)	$ (494)

Financial Instruments And Inv46

Financial Instruments And Investments (Marketable Securities Fair Value and Unrecognized Gross Unrealized Gains) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Gross Unrealized Gain	$ 42,707	$ 38,667
Marketable Securities Fair Value, Total	186,449	144,628
Debt Securities
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	46,686	34,498
Available-for-sale Securities, Gross Unrealized Gain	1,739	1,256
Federal Agency Mortgage Backed Securities
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	6,662	7,430
Available-for-sale Securities, Gross Unrealized Gain	272	319
U.S. Government Bonds
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	13,846	12,237
Available-for-sale Securities, Gross Unrealized Gain	311	138
Municipal Obligations
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	5,197	2,481
Available-for-sale Securities, Gross Unrealized Gain	161	144
Corporate Obligations
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	20,981	12,350
Available-for-sale Securities, Gross Unrealized Gain	995	655
Common Stock
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	53,489	61,884
Available-for-sale Securities, Gross Unrealized Gain	30,766	34,066
Equity Mutual Funds
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	54,236	42,244
Available-for-sale Securities, Gross Unrealized Gain	7,028	3,345
Institutional Funds-International Equity
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	26,149	0
Available-for-sale Securities, Gross Unrealized Gain	3,174	0
Cash
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Gross Unrealized Gain	0	0
Cash | Held in trust Decommissioning Fund Investment
Financial Instruments and Investments [Line Items]
Cash	$ 5,889	$ 6,002

Financial Instruments And Inv47

Financial Instruments And Investments (Contractual Year For Maturity Of Available-For-Sale Securities ) (Details) $ in Thousands	Jun. 30, 2017USD ($)
U.S. Government Bonds
Schedule of Available-for-sale Securities [Line Items]
Total	$ 59,050
2,017	5,893
2018 through 2021	24,224
2022 through 2026	15,981
2027 and Beyond	12,952
Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Total	18,028
2,017	796
2018 through 2021	6,215
2022 through 2026	9,743
2027 and Beyond	1,274
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total	31,233
2,017	0
2018 through 2021	12,309
2022 through 2026	8,949
2027 and Beyond	9,975
Federal Agency Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Total	22,523
2,017	0
2018 through 2021	5
2022 through 2026	338
2027 and Beyond	$ 22,180

Financial Instruments And Inv48

Financial Instruments And Investments (Sale Of Securities And The Related Effects On Pre-Tax Income ) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Investment [Line Items]
Proceeds from sales or maturities of available-for-sale securities	$ 36,476	$ 16,634	$ 62,531	$ 40,712	$ 113,087	$ 106,121
Gross realized gains included in pre-tax income	5,322	2,409	7,909	4,241	12,880	12,805
Gross realized losses included in pre-tax income	(156)	(299)	(552)	(587)	(1,185)	(1,262)
Gross unrealized losses included in pre-tax income	0	0	0	(156)	(196)	(494)
Net gains included in pre-tax income	5,166	2,110	7,357	3,498	11,499	11,049
Net unrealized holding gains (losses) included in accumulated other comprehensive income	4,458	2,790	12,179	4,980	15,643	2,623
Net gains reclassified from accumulated other comprehensive income	(5,166)	(2,110)	(7,357)	(3,498)	(11,499)	(11,049)
Net gains (losses) in other comprehensive income	$ (708)	$ 680	$ 4,822	$ 1,482	$ 4,144	$ (8,426)

Financial Instruments And Inv49

Financial Instruments And Investments (Company's Decommissioning Trust Funds And Investments In Debt Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	$ 271,315	$ 255,708
Decommisioning Fund Investments | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	199,531	197,703
Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	71,784	58,005
Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Debt Securities
Financial Instruments and Investments [Line Items]
Trading Securities	1,538	1,421
Debt Securities | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Trading Securities	0	0
Debt Securities | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Trading Securities	0	0
Debt Securities | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Trading Securities	1,538	1,421
Debt Securities | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	130,834	119,873
Debt Securities | Decommisioning Fund Investments | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	59,050	61,868
Debt Securities | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	71,784	58,005
Debt Securities | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Federal Agency Mortgage Backed Securities | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	22,523	19,448
Federal Agency Mortgage Backed Securities | Decommisioning Fund Investments | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Federal Agency Mortgage Backed Securities | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	22,523	19,448
Federal Agency Mortgage Backed Securities | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
US Treasury and Government | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	59,050	61,868
US Treasury and Government | Decommisioning Fund Investments | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	59,050	61,868
US Treasury and Government | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
US Treasury and Government | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Municipal Obligations | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	18,028	16,144
Municipal Obligations | Decommisioning Fund Investments | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Municipal Obligations | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	18,028	16,144
Municipal Obligations | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Corporate Obligations | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	31,233	22,413
Corporate Obligations | Decommisioning Fund Investments | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Corporate Obligations | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	31,233	22,413
Corporate Obligations | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Common Stock | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	54,207	64,644
Common Stock | Decommisioning Fund Investments | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	54,207	64,644
Common Stock | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Common Stock | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Equity Funds | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	54,236	42,244
Equity Funds | Decommisioning Fund Investments | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	54,236	42,244
Equity Funds | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Equity Funds | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Institutional Funds-International Equity | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	26,149	22,945
Institutional Funds-International Equity | Decommisioning Fund Investments | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	26,149	22,945
Institutional Funds-International Equity | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Institutional Funds-International Equity | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Cash | Held in trust Decommissioning Fund Investment
Financial Instruments and Investments [Line Items]
Cash	5,889	6,002
Cash | Held in trust Decommissioning Fund Investment | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Cash	5,889	6,002
Cash | Held in trust Decommissioning Fund Investment | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Cash	0	0
Cash | Held in trust Decommissioning Fund Investment | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Cash	$ 0	$ 0

Financial Instruments And Inv50

Financial Instruments And Investments Transfers Between Levels (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value Disclosures [Abstract]
Fair Value, Assets, Level 1 to Level 2 Transfers, Description	no	no	no	no	no	no
Fair Value, Assets, Level 2 to Level 1 Transfers, Description	no	no	no	no	no	no
Fair Value, Asset, Level 3 Purchases, (Sales), Issuances, (Settlements)	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0