El Paso Electric 10-Q 4 Nov 16 2016 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2016	Oct. 31, 2016
Document and Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q3
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		40,522,246

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Utility plant:
Electric plant in service	$ 3,746,141	$ 3,616,301
Less accumulated depreciation and amortization	(1,228,659)	(1,329,843)
Net plant in service	2,517,482	2,286,458
Construction work in progress	153,868	293,796
Nuclear fuel; includes fuel in process of $64,292 and $51,854, respectively	201,993	190,282
Less accumulated amortization	(85,895)	(75,031)
Net nuclear fuel	116,098	115,251
Net utility plant	2,787,448	2,695,505
Current assets:
Cash and cash equivalents	10,044	8,149
Accounts receivable, principally trade, net of allowance for doubtful accounts of $2,260 and $2,046, respectively	112,697	66,326
Inventories, at cost	47,498	48,697
Under-collection of fuel revenues	8,962	0
Prepayments and other	12,856	9,872
Total current assets	192,057	133,044
Deferred charges and other assets:
Decommissioning trust funds	254,626	239,035
Regulatory assets	122,054	115,127
Other	16,488	17,896
Total deferred charges and other assets	393,168	372,058
Total assets	3,372,673	3,200,607
Capitalization:
Common stock, stated value $1 per share, 100,000,000 shares authorized, 65,671,235 and 65,709,819 shares issued, and 156,976 and 118,834 restricted shares, respectively	65,828	65,829
Capital in excess of stated value	321,629	320,073
Retained earnings	1,121,487	1,067,396
Accumulated other comprehensive loss, net of tax	(12,337)	(13,914)
Total stockholders' equity subtotal before treasury stock	1,496,607	1,439,384
Treasury stock, 25,305,965 and 25,384,834 shares, respectively, at cost	(421,532)	(422,846)
Common stock equity	1,075,075	1,016,538
Long-term debt, net of current portion	1,195,397	1,122,660
Total capitalization	2,270,472	2,139,198
Current liabilities:
Current maturities of long-term debt	83,081	0
Short-term borrowings under the revolving credit facility	55,192	141,738
Accounts payable, principally trade	70,486	59,978
Taxes accrued	35,127	30,351
Interest accrued	19,349	12,649
Over-collection of fuel revenues	1,219	4,023
Other	29,543	28,325
Total current liabilities	293,997	277,064
Deferred credits and other liabilities:
Accumulated deferred income taxes	549,846	495,237
Accrued pension liability	83,366	90,527
Accrued post-retirement benefit liability	56,398	54,553
Asset retirement obligation	80,086	81,621
Regulatory liabilities	18,495	24,303
Other	20,013	38,104
Total deferred credits and other liabilities	808,204	784,345
Commitments and contingencies
Total capitalization and liabilities	$ 3,372,673	$ 3,200,607

Balance Sheets Parenthetical

Balance Sheets Parenthetical - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Nuclear fuel; fuel in process	$ 64,292	$ 51,854
Allowance for Doubtful Accounts Receivable, Current	$ 2,260	$ 2,046
Common Stock, Par or Stated Value Per Share	$ 1	$ 1
Common Stock, Shares Authorized	100,000,000	100,000,000
Common Stock, Shares, Issued	65,671,235	65,709,819
Common stock, restricted shares	156,976	118,834
Treasury Stock, Shares	25,305,965	25,384,834

Statements Of Operations

Statements Of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Operating revenues	$ 323,225	$ 289,713	$ 698,899	$ 672,967	$ 875,801	$ 869,530
Energy expenses:
Fuel	54,355	60,798	131,817	148,340	171,877	207,564
Purchased and interchanged power	24,459	19,520	47,715	42,437	58,823	53,127
Cost of services, energy services	78,814	80,318	179,532	190,777	230,700	260,691
Operating revenues net of energy expenses	244,411	209,395	519,367	482,190	645,101	608,839
Other operating expenses:
Other operations	64,373	65,360	179,577	178,615	243,912	241,510
Maintenance	14,064	14,355	52,005	49,772	67,456	69,782
Depreciation and amortization	15,952	22,380	63,097	67,080	85,841	88,086
Taxes other than income taxes	20,165	19,253	50,297	48,844	65,189	62,711
Utilities operating expense	114,554	121,348	344,976	344,311	462,398	462,089
Operating income	129,857	88,047	174,391	137,879	182,703	146,750
Other income (deductions):
Allowance for equity funds used during construction	1,398	1,874	5,867	8,417	8,089	12,864
Investment and interest income, net	3,773	5,912	10,293	12,564	15,237	17,660
Miscellaneous non-operating income	272	850	1,073	1,537	1,598	3,453
Miscellaneous non-operating deductions	(1,312)	(1,015)	(2,668)	(2,777)	(4,219)	(4,922)
Nonoperating income (expense)	4,131	7,621	14,565	19,741	20,705	29,055
Interest charges (credits):
Interest on long-term debt and revolving credit facility	18,324	16,465	53,221	49,443	69,629	64,668
Other interest	268	424	1,102	941	1,474	1,292
Capitalized interest	(1,243)	(1,208)	(3,738)	(3,758)	(4,948)	(5,053)
Allowance for borrowed funds used during construction	(1,131)	(1,353)	(4,164)	(5,365)	(5,736)	(7,892)
Interest expense	16,218	14,328	46,421	41,261	60,419	53,015
Income before income taxes	117,770	81,340	142,535	116,359	142,989	122,790
Income tax expense	43,134	24,600	51,423	35,089	51,229	37,279
Net income	$ 74,636	$ 56,740	$ 91,112	$ 81,270	$ 91,760	$ 85,511
Basic earnings per share	$ 1.840	$ 1.400	$ 2.250	$ 2.010	$ 2.270	$ 2.120
Diluted earnings per share	1.840	1.400	2.250	2.010	2.270	2.120
Dividends declared per share of common stock	$ 0.310	$ 0.295	$ 0.915	$ 0.870	$ 1.210	$ 1.150
Weighted average number of shares outstanding	40,363,819	40,289,010	40,344,834	40,267,533	40,332,835	40,255,439
Weighted average number of shares and dilutive potential shares outstanding	40,425,942	40,329,529	40,395,811	40,299,801	40,380,443	40,279,640

Statements Of Comprehensive Ope

Statements Of Comprehensive Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net income	$ 74,636	$ 56,740	$ 91,112	$ 81,270	$ 91,760	$ 85,511
Unrecognized pension and post-retirement benefit costs:
Net gain (loss) arising during period	0	0	0	0	5,429	(74,028)
Prior service benefit	0	0	0	0	824	34,200
Reclassification adjustments included in net income for amortization of:
Prior service benefit	(1,663)	(1,606)	(4,993)	(4,931)	(6,636)	(6,996)
Net loss	1,087	1,966	3,532	6,466	5,688	8,081
Net unrealized gains/losses on marketable securities:
Net holding gains (losses) arising during period	4,313	(8,092)	9,293	(8,641)	15,028	(5,779)
Reclassification adjustments for net gains included in net income	(2,072)	(4,324)	(5,570)	(7,887)	(8,797)	(11,446)
Net losses on cash flow hedges:
Reclassification adjustment for interest expense included in net income	126	118	371	348	490	460
Total other comprehensive income (loss) before income taxes	1,791	(11,938)	2,633	(14,645)	12,026	(55,508)
Income tax benefit (expense) related to items of other comprehensive income (loss):
Unrecognized pension and post-retirement benefit costs	(228)	(134)	(6)	(756)	(2,536)	14,456
Net unrealized losses (gains) on marketable securities	(435)	2,459	(757)	3,340	(1,269)	3,469
Losses on cash flow hedges	(165)	(46)	(293)	(161)	(335)	(201)
Total income tax benefit (expense)	(828)	2,279	(1,056)	2,423	(4,140)	17,724
Other comprehensive income (loss), net of tax	963	(9,659)	1,577	(12,222)	7,886	(37,784)
Comprehensive income	$ 75,599	$ 47,081	$ 92,689	$ 69,048	$ 99,646	$ 47,727

Statements Of Cash Flows

Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net income	$ 91,112	$ 81,270
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of electric plant in service	63,097	67,080
Amortization of nuclear fuel	33,088	32,864
Deferred income taxes, net	48,457	32,090
Allowance for equity funds used during construction	(5,867)	(8,417)
Other amortization and accretion	12,102	13,273
Gain on sale of property, plant and equipment	(545)	(587)
Net gains on sale of decommissioning trust funds	(5,570)	(7,887)
Other operating activities	871	387
Change in:
Accounts receivable	(46,371)	(33,156)
Inventories	(16)	(3,226)
Net over-collection (under-collection) of fuel revenues	(11,766)	10,934
Prepayments and other	(4,467)	(5,401)
Accounts payable	6,994	(14,397)
Taxes accrued	4,560	8,747
Interest accrued	6,700	4,078
Other current liabilities	1,218	2,005
Deferred charges and credits	(16,817)	(3,227)
Net cash provided by operating activities	176,780	176,430
Cash flows from investing activities:
Cash additions to utility property, plant and equipment	(168,830)	(211,516)
Cash additions to nuclear fuel	(29,929)	(30,483)
Capitalized interest and AFUDC:
Utility property, plant and equipment	10,031	13,782
Nuclear fuel	(3,738)	(3,758)
Allowance for equity funds used during construction	5,867	8,417
Decommissioning trust funds:
Purchases, including funding of $3.4 million	(66,463)	(70,016)
Sales and maturities	60,165	63,776
Proceeds from sale of property, plant, and equipment	3,251	644
Other investing activities	3,383	(627)
Net cash used for investing activities	(206,325)	(257,345)
Cash flows from financing activities:
Dividends paid	(37,021)	(35,138)
Borrowings under the revolving credit facility:
Proceeds	269,977	266,779
Payments	(356,523)	(162,618)
Payment on maturing RGRT senior notes	0	15,000
Proceeds from issuance of senior notes	157,052	0
Other financing activities	(2,045)	(1,039)
Net cash provided by financing activities	31,440	52,984
Net increase (decrease) in cash and cash equivalents	1,895	(27,931)
Cash and cash equivalents at beginning of period	8,149	40,504
Cash and cash equivalents at end of period	$ 10,044	$ 12,573

Statements Of Cash Flows Parent

Statements Of Cash Flows Parenthetical - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Payments To Fund Decommissioning Fund	$ 3.4	$ 3.4

Principles Of Preparation

Principles Of Preparation	9 Months Ended
	Sep. 30, 2016
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, 2015 (the " 2015 Form 10-K"). Capitalized terms used in this report and not defined herein have the meaning ascribed to such terms in the 2015 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 September 30, 2016 and December 31, 2015 ; the results of its operations and comprehensive operations for the three, nine and twelve months ended September 30, 2016 and 2015 ; and its cash flows for the nine months ended September 30, 2016 and 2015 . The results of operations and comprehensive operations for the three and nine months ended September 30, 2016 and the cash flows for the nine months ended September 30, 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 (the "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. Use of Estimates . The preparation of financial statements in conformity with generally accepted accounting principles 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 $30.3 million at September 30, 2016 and $21.7 million at December 31, 2015 . 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. Based, in part, upon a 2014 study performed for the Company, the Company modified certain salvage values related to both interim and final removal costs and service lives which were approved by the Company's regulators in 2016. The effect of the change in these estimates resulted in reducing depreciation expense approximately $7.4 million for the nine months ended September 30, 2016. The Company expects that the 2016 annual reduction to depreciation expense to approximate $9.5 million . Income Taxes . The Company accounts for federal and state income taxes under the asset and liability method of accounting for income taxes. Deferred income taxes are recognized for the estimated future tax consequences of "temporary differences" by applying enacted statutory tax rates for each taxable jurisdiction applicable to future years to differences between the financial statement carrying amounts and the tax basis of existing assets and liabilities. Historically, certain temporary differences are accorded flow-through treatment by the Company's regulators and impact the Company's effective tax rate. The Financial Accounting Standards Board ("FASB") guidance requires that rate-regulated companies record deferred income taxes for temporary differences accorded flow-through treatment at the direction of the regulatory commission. The resulting deferred tax assets and liabilities are recorded at the expected cash flow to be reflected in future rates. Because the Company's regulators have consistently permitted the recovery of tax effects previously flowed-through earnings, the Company has recorded regulatory liabilities and assets offsetting such deferred tax assets and liabilities. During 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 Company's regulators in its most recent final orders from the Public Utility Commission of Texas ("PUCT") and the New Mexico Public Regulation Commission ("NMPRC"). Accordingly, the Company recorded deferred state income tax expense as required by normalization, retroactive to January 2016 as provided in the final orders. See Note F for further discussion. The effect on deferred tax assets and liabilities of a change in tax rate is recognized in income in the period that includes the enactment date. The Company recognizes tax assets and liabilities for uncertain tax positions in accordance with the recognition and measurement criteria of the FASB guidance for uncertainty in income taxes. See Note F. Supplemental Cash Flow Disclosures (in thousands) Nine Months Ended September 30, 2016 2015 Cash paid (received) for: Interest on long-term debt and borrowings under the revolving credit facility $ 46,867 $ 41,406 Income tax paid (refunded), net 3,337 (272 ) Non-cash investing and financing activities: Sale of Interest in Four Corners Generating Station (a) 27,720 — Changes in accrued plant additions 4,277 (13,150 ) Grants of restricted shares of common stock 1,236 1,106 (a) The Company sold its interest in the Four Corners Generating Station ("Four Corners") for approximately $32.0 million based on the book value as defined in the asset purchase agreement entered into by the Company and Arizona Public Service Company ("APS") on February 17, 2015 (the "Purchase and Sale Agreement"). The sales price was adjusted downward by $7.0 million and $19.5 million , respectively, to reflect APS assumption of the Company's obligation to pay for future plant decommissioning and mine reclamation expense. The sales price was also adjusted downward by approximately $1.3 million for closing adjustments and other assets and liabilities assumed by APS. At the closing of the sale, the Company received approximately $4.2 million in cash, subject to post-closing adjustments. Subsequently, the Company recorded post-closing adjustments to reflect adjustments to estimated capital expenditures and other assets and liabilities assumed by APS through July 6, 2016, which resulted in a $1.6 million refund due to APS. New Accounting Standards. In April 2015, the FASB issued Accounting Standards Update ("ASU") 2015-03, Interest - Imputation of Interest (Topic 715) to simplify the presentation of debt issuance costs. ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by this ASU. ASU 2015-03 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. In August 2015, the FASB issued ASU 2015-15, Interest - Imputation of Interest (Subtopic 835-30), to provide further clarification to ASU 2015-03 as it relates to the presentation and subsequent measurement of debt issuance costs associated with line of credit arrangements. The Company implemented ASU 2015-03 and ASU 2015-15 in the first quarter of 2016, retrospectively to all prior periods presented in the Company's Balance Sheet. The implementation of ASU 2015-03 did not have an impact on the Company's results of operations. See Note J. In November 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes to simplify the presentation of deferred income taxes. ASU 2015-17 requires that deferred tax liabilities and assets be classified as noncurrent in a classified statement of financial position. ASU 2015-17 can be applied prospectively or retrospectively and is effective for financial statements issued for annual periods beginning after December 15, 2016 and interim periods within those annual periods and early adoption is permitted . The Company elected to early adopt ASU 2015-17 retrospectively in the first quarter of 2016 in the Company's Balance Sheet. The implementation of ASU 2015-17 did not have an impact on the Company's results of operations. See Note F. 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. ASU 2014-09 is the result of a joint effort by the FASB and the International Accounting Standards Board intended to clarify the principles for recognizing revenue and to develop a common revenue standard for U.S. Generally Accepted Accounting Principles ("GAAP") and International Financial Reporting Standards. ASU 2014-09 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. ASU 2014-09 was originally intended to be effective for annual periods and interim periods within that reporting period beginning after December 15, 2016, for public business entities. In August 2015, FASB issued ASU 2015-14 to defer the effective date of ASU 2014-09 for all entities by one year. Public business entities will apply the guidance in ASU 2014-09 to annual reporting periods beginning after December 15, 2017 and interim periods within that reporting period. In March 2016, the FASB issued ASU 2016-08 to clarify the implementation guidance on principal versus agent consideration. In April 2016, the FASB issued ASU 2016-10 to clarify the implementation guidance on identifying performance obligations and licensing. In May 2016, the FASB issued ASU 2016-11, which rescinds certain SEC Staff Observer comments that are codified in FASB ASC Topic 605 (Revenue Recognition), effective upon adoption of Topic 606. In May 2016, the FASB issued ASU 2016-12, which makes narrow-scope amendments to ASU 2014-09, and provides practical expedients to simplify the transition to the new standard and to clarify certain aspects of the standard. Early adoption of ASU 2014-09 is permitted after December 15, 2016. The Company has not selected a transition method and is currently assessing the future impact of this ASU. 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 standard includes a requirement that businesses must report changes in the fair value of their own liabilities in other comprehensive income instead of earnings, and this is the only provision of the update for which the FASB is permitting early adoption. The remaining provisions of this ASU become effective for public companies for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The Company is currently assessing 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 (the 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. 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 for public companies will be required for annual reporting periods beginning after December 15, 2018 and interim periods within that reporting period. Early adoption of ASU 2016-02 is permitted for all entities. 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 assessing the future impact of this ASU. In March 2016, the FASB issued 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. This ASU is effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods. Early adoption is permitted. The Company is currently assessing the future impact of this ASU. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326). ASU 2016-13 significantly 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. For public business entities, the provisions of ASU 2016-13 are effective for fiscal years and interim periods within that reporting period beginning after December 15, 2019. Early implementation is permitted as of the fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. 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 this ASU. 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 new guidance addresses the following classification issues: debt prepayment or debt extinguishment costs; settlement of zero-coupon bonds; contingent consideration payments made after a business combination; proceeds from the settlement of insurance claims; proceeds from the settlement of corporate-owned life insurance policies, including bank-owned life insurance policies; distributions received from equity method investees; beneficial interests in securitization transactions; and separately identifiable cash flows and application of the predominance principle. For public business entities, the provisions of ASU 2016-15 are effective for fiscal years and interim periods within that reporting period beginning after December 15, 2017. Early adoption is permitted, including adoption in an interim period. If an entity elects early adoption of ASU 2016-15 in an interim period, adjustments should be reflected as of the beginning of the fiscal year that includes that interim period. An entity that elects early adoption must adopt all of the amendments in the same period. 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. Reclassification. Certain amounts in the financial statements for 2015 have been reclassified to conform to the 2016 presentation. The Company implemented ASU 2015-03 and ASU 2015-17 in the first quarter of 2016, retrospectively to all periods presented in the Company's financial statements. See Note F and Note J, respectively.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Notes)	9 Months Ended
	Sep. 30, 2016
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 September 30, 2016 Three Months Ended September 30, 2015 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 (loss) before reclassifications — 3,493 — 3,493 — (6,485 ) — (6,485 ) Amounts reclassified from accumulated other comprehensive income (loss) (804 ) (1,687 ) (39 ) (2,530 ) 226 (3,472 ) 72 (3,174 ) Balance at end of period $ (31,336 ) $ 30,731 $ (11,732 ) $ (12,337 ) $ (34,105 ) $ 25,769 $ (11,887 ) $ (20,223 ) Nine Months Ended September 30, 2016 Nine Months Ended September 30, 2015 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 $ (29,869 ) $ 27,765 $ (11,810 ) $ (13,914 ) $ (34,884 ) $ 38,957 $ (12,074 ) $ (8,001 ) Other comprehensive income (loss) before reclassifications — 7,459 — 7,459 — (6,854 ) — (6,854 ) Amounts reclassified from accumulated other comprehensive income (loss) (1,467 ) (4,493 ) 78 (5,882 ) 779 (6,334 ) 187 (5,368 ) Balance at end of period $ (31,336 ) $ 30,731 $ (11,732 ) $ (12,337 ) $ (34,105 ) $ 25,769 $ (11,887 ) $ (20,223 ) Twelve Months Ended September 30, 2016 Twelve Months Ended September 30, 2015 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 $ (34,105 ) $ 25,769 $ (11,887 ) $ (20,223 ) $ (9,818 ) $ 39,525 $ (12,146 ) $ 17,561 Other comprehensive income (loss) before reclassifications 3,777 12,058 — 15,835 (24,775 ) (4,537 ) — (29,312 ) Amounts reclassified from accumulated other comprehensive income (loss) (1,008 ) (7,096 ) 155 (7,949 ) 488 (9,219 ) 259 (8,472 ) Balance at end of period $ (31,336 ) $ 30,731 $ (11,732 ) $ (12,337 ) $ (34,105 ) $ 25,769 $ (11,887 ) $ (20,223 ) Amounts reclassified from Accumulated Other Comprehensive Income (Loss) for the three, nine and twelve months ended September 30, 2016 and 2015 are as follows (in thousands): Details about Accumulated Other Comprehensive Income (Loss) Components Three Months Ended September 30, Nine Months Ended September 30, Twelve Months Ended September 30, Affected Line Item in the Statement of Operations 2016 2015 2016 2015 2016 2015 Amortization of pension and post-retirement benefit costs: Prior service benefit $ 1,663 $ 1,606 $ 4,993 $ 4,931 $ 6,636 $ 6,996 (a) Net loss (1,087 ) (1,966 ) (3,532 ) (6,466 ) (5,688 ) (8,081 ) (a) 576 (360 ) 1,461 (1,535 ) 948 (1,085 ) (a) Income tax effect 228 134 6 756 60 597 Income tax expense 804 (226 ) 1,467 (779 ) 1,008 (488 ) (a) Marketable securities: Net realized gain on sale of securities 2,072 4,324 5,570 7,887 8,797 11,446 Investment and interest income, net 2,072 4,324 5,570 7,887 8,797 11,446 Income before income taxes Income tax effect (385 ) (852 ) (1,077 ) (1,553 ) (1,701 ) (2,227 ) Income tax expense 1,687 3,472 4,493 6,334 7,096 9,219 Net income Loss on cash flow hedge: Amortization of loss (126 ) (118 ) (371 ) (348 ) (490 ) (460 ) Interest on long-term debt and revolving credit facility (126 ) (118 ) (371 ) (348 ) (490 ) (460 ) Income before income taxes Income tax effect 165 46 293 161 335 201 Income tax expense 39 (72 ) (78 ) (187 ) (155 ) (259 ) Net income Total reclassifications $ 2,530 $ 3,174 $ 5,882 $ 5,368 $ 7,949 $ 8,472 (a) These items are included in the computation of net periodic benefit cost. See Note I, Employee Benefits, for additional information.

Regulation

Regulation	9 Months Ended
	Sep. 30, 2016
Public Utilities, General Disclosures [Abstract]
Regulation	Regulation General The rates and services of the Company are regulated by incorporated municipalities in Texas, the PUCT, the 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 of approximately $71.5 million . On January 15, 2016, the Company filed its rebuttal testimony modifying the requested increase to $63.3 million . On August 25, 2016 , the PUCT issued its final order in Docket No. 44941 (the "PUCT Final Order"), as proposed, approving the Joint Motion to Implement Uncontested Amended and Restated Stipulation and Agreement (the "Unopposed Settlement") that was filed with the PUCT on July 21, 2016 , which was unopposed by the parties to the rate case. The PUCT Final Order provides for the following: (i) an annual non-fuel rate increase of $37 million , lower annual depreciation expense of approximately $8.5 million , a return on equity of 9.7% for AFUDC purposes, and 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 costs, which will be collected through a surcharge that terminates on July 12, 2017 and applies to consumption on and after January 12, 2016; (iii) removal of the separate rate treatment for residential customers with solar systems; (iv) recovery of $3.1 million in rate case expenses through a separate surcharge; and (v) recovery of revenues associated with the relate back of rates to consumption on and after January 12, 2016 through March 31, 2016 (aggregating $4.8 million ) through a separate surcharge, all as specified in the Unopposed Settlement. The costs of serving residential customers with solar generation will be addressed in a future proceeding. Interim rates associated with the annual non-fuel rate increase of $37 million 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 . Given the uncertainties regarding the ultimate resolution of the rate case, the Company did not recognize the impacts of the Unopposed Settlement in the Statements of Operations until it received the PUCT Final Order on August 25, 2016 . Accordingly, operating revenues increased approximately $34.8 million , depreciation decreased approximately $7.4 million , and other expenses, net, increased approximately $1.9 million for an aggregate increase in income before income taxes of $40.3 million and an increase in net income of $23.3 million in the third quarter of 2016 to reflect the effects of the PUCT Final Order. Energy Efficiency Cost Recovery Factor. On May 1, 2015, the Company filed its annual application to establish its energy efficiency cost recovery factor for 2016. In addition to projected energy efficiency costs for 2016 and a true-up to prior year actual costs, the Company requested approval of a $1.0 million bonus for the 2014 energy efficiency program results in accordance with PUCT rules. This case was assigned PUCT Docket No. 44677. A stipulation and settlement agreement was filed September 24, 2015 and the PUCT approved the settlement on November 5, 2015. The settlement approved by the PUCT includes a performance bonus of $1.0 million . The Company recorded the performance bonus as operating revenue in the fourth quarter of 2015. On April 29, 2016, the Company filed its annual application to establish its energy efficiency cost recovery factor for 2017. In addition to projected energy efficiency costs for 2017 and true-up to prior year actual costs, the Company requested approval of a $668 thousand bonus for the 2015 energy efficiency program results in accordance with PUCT rules. This case was assigned PUCT Docket No. 45885. Parties in the proceeding, including PUCT staff and the City of El Paso, have filed a settlement in the case that approves the Company's filed proposal with a reduction to the 2015 program bonus of $155 thousand . The PUCT approved the settlement on October 28, 2016. The settlement approved by the PUCT includes a performance bonus of $0.5 million . The Company recorded the performance bonus as operating revenue in the third quarter of 2016. Fuel and Purchased Power Costs. The Company's actual fuel costs, including purchased power energy costs, are recovered from customers through a fixed fuel factor. The PUCT has adopted a fuel cost recovery rule (the "Texas Fuel Rule") that allows the Company to seek periodic adjustments to its fixed fuel factor. The Company can seek to revise its fixed fuel factor based upon the approved formula at least four months after its last revision except in the month of December. The Texas Fuel Rule requires the Company to request to refund fuel costs in any month when the over-recovery balance exceeds a threshold material amount and it expects fuel costs to continue to be materially over-recovered. The Texas Fuel Rule also permits the Company to seek to surcharge fuel under-recoveries in any month the balance exceeds a threshold material amount and it expects fuel cost recovery to continue to be materially under-recovered. Fuel over- and under-recoveries are considered material when they exceed 4% of the previous twelve months' fuel costs. All such fuel revenue and expense activities are subject to periodic final review by the PUCT in fuel reconciliation proceedings. On April 15, 2015, the Company filed a request, which was assigned PUCT Docket No. 44633, to reduce its fixed fuel factor by approximately 24% to reflect reduced fuel expenses primarily related to a reduction in the price of natural gas used to generate power. The over-recovered balance was below the PUCT's materiality threshold. The reduction in the fixed fuel factor was effective on an interim basis May 1, 2015 and approved by the PUCT on May 20, 2015 . As of September 30, 2016 , the Company had under-recovered fuel costs in the amount of $8.9 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 fuel and purchased power expenses incurred during the period of April 1, 2013 through March 31, 2016 . Montana Power Station Approvals . T he Company has received a Certificate of Convenience and Necessity ("CCN") from the PUCT to construct four natural gas fired generating units at Montana Power Station ("MPS") in El Paso County, Texas. The Company also obtained air permits from the Texas Commission on Environmental Quality (the "TCEQ") and the U.S. Environmental Protection Agency (the "EPA"). MPS Units 1 and 2 and associated transmission lines and common facilities were completed and placed into service in March 2015 . MPS Units 3 and 4 were completed and placed into service on May 3, 2016 and September 15, 2016 , respectively. Community Solar. On June 8, 2015, the Company filed a petition with the PUCT to initiate a community solar program to include construction and ownership of a 3 MW solar photovoltaic system located at MPS. 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. Four Corners Generating Station. On February 17, 2015 , the Company and APS entered the Purchase and Sale Agreement providing for purchase by APS of the Company's interests in Four Corners. The Four Corners transaction closed on July 6, 2016 . See Note D for further details on the sale of Four Corners. 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 mine reclamation costs, in the Company's next rate case, which is expected to be filed in the first half of 2017. The procedural schedule related to the public interest issues called for a hearing to be held on October 6-7, 2016. However, on September 1, 2016, a motion by parties in the proceeding to suspend the procedural schedule in order to pursue settlement was approved by the PUCT. At September 30, 2016 , the regulatory asset associated with the Four Corners mine reclamation costs for our Texas jurisdiction approximated $7.5 million . The Company currently continues to recover its mine reclamation costs in Texas under previous orders and decisions of the PUCT. If any future determinations made by our regulators result in changes to how existing regulatory assets or previously incurred costs for Four Corners are recovered in rates, any such changes would be recognized only when it becomes probable future cash flows will change as a result of such regulatory actions. Other Required Approvals . The Company has obtained other required approvals for tariffs and approvals as required by the Public Utility Regulatory Act (the "PURA") and the PUCT. New Mexico Regulatory Matters 2015 New Mexico Rate Case Filing . On May 11, 2015, the Company filed with the NMPRC in Case No. 15-00127-UT, for an annual increase in non-fuel base rates of approximately $8.6 million or 7.1% . Subsequently, the Company reduced its requested increase in non-fuel base rates to approximately $6.4 million . On June 8, 2016, the NMPRC issued its final order approving an annual increase in non-fuel base rates of approximately $1.1 million and a decrease in the Company's allowed return on equity to 9.48% . The final order concludes that all of the Company's new plant in service was reasonable and necessary and therefore would be recoverable in rate base. The Company's rates were approved by the NMPRC effective July 1, 2016 and implemented at such time. Fuel and Purchased Power Costs. On January 8, 2014, the NMPRC approved the continuation of the Fuel and Purchased Power Cost Adjustment Clause (the "FPPCAC") without modification in NMPRC Case No. 13-00380-UT. Historically, fuel and purchased power costs were recovered through base rates and a 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 of Case No. 15-00127-UT, fuel and purchased power costs will no longer be recovered through base rates but will be completely recovered through the FPPCAC. Fuel and purchased power costs are reconciled to actual costs on a monthly basis and recovered or refunded to customers the second succeeding month. The Company recovers costs related to Palo Verde Unit 3 capacity and energy in New Mexico through the FPPCAC as purchased power using a proxy market price approved in Case No. 13-00380-UT. At September 30, 2016 , the Company had a net fuel over-recovery balance of $1.3 million in New Mexico. Montana Power Station Approvals. The Company has received a CCN from the NMPRC to construct four units at MPS and the associated transmission lines. The Company also obtained all necessary air permits from the TCEQ and the EPA. A final order in NMPRC Case No. 13-00297-UT approving the CCN for MPS Units 3 and 4 was issued on June 11, 2014. MPS Units 1 and 2 were completed and placed into service in March 2015 . MPS Units 3 and 4 were completed and placed into service on May 3, 2016 and September 15, 2016 , respectively. Four Corners. On February 17, 2015 , the Company and APS entered into the Purchase and Sale Agreement providing for the purchase by APS of the Company's interests in Four Corners. On April 27, 2015, the Company filed an application in NMPRC Case No. 15-00109-UT requesting all necessary regulatory approvals to sell its ownership interest in Four Corners. On February 2, 2016, the Company filed a joint stipulation with the NMPRC reflecting a settlement agreement among the NMPRC's Utility Division Staff, the Company and the New Mexico Attorney General proposing approval of abandonment and sale of its seven percent minority ownership interest in Four Corners Units 4 and 5 and common facilities to APS. A hearing in the case was held on February 16, 2016, and the Hearing Examiner issued a Certification of Stipulation on April 22, 2016 recommending approval of the joint stipulation without modification. On June 15, 2016, the NMPRC issued its final order approving the stipulation. See Note D for further details on the sale of Four Corners. 5 MW Holloman Air Force Base ("HAFB") Facility CCN . On June 15, 2015, the Company filed a petition with the NMPRC requesting CCN authorization to construct a 5 MW solar-powered generation facility to be located at HAFB in the Company's service territory in New Mexico. The new facility will be a dedicated Company-owned resource serving HAFB. This case was assigned NMPRC Case No. 15-00185-UT. On October 7, 2015, the NMPRC issued a final order accepting the Hearing Examiner’s Recommended Decision to approve the CCN, as modified. The Company and HAFB negotiated a special retail contract, which includes power sales agreement for the facility, to replace the existing load retention agreement and requested approval in NMPRC Case No. 16-00224-UT. On October 5, 2016 the new agreement was approved by the NMPRC. Construction of the solar generation facility will begin in the fourth quarter of 2016 and is expected to be completed in the second quarter of 2017. Issuance of Long-Term Debt and Guarantee of Debt. On October 7, 2015, the Company received approval in NMPRC Case No. 15-00280-UT to issue up to $310 million in new long-term debt; and to guarantee the issuance of up to $65 million of new debt by Rio Grande Resources Trust ("RGRT") to finance future purchases of nuclear fuel and to refinance existing nuclear fuel debt obligations. This approval supersedes prior approvals. Under this authorization, on March 24, 2016 , the Company issued $150 million in aggregate principal amount of 5.00% Senior Notes due December 1, 2044 . The net proceeds from the issuance of these senior notes, after deducting the underwriters' commission, were $158.1 million . These proceeds include accrued interest of $2.4 million and a $7.1 million premium before expenses. These senior notes constitute an additional issuance of the Company's 5.00% Senior Notes due 2044 , of which $150 million was previously issued on December 1, 2014 , for a total principal amount outstanding of $300 million . 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 Four Corners. On June 26, 2015, APS filed an application requesting authorization from FERC to purchase 100% of the Company’s ownership interest in Units 4 and 5 of Four Corners and the associated transmission interconnection facilities and rights. On December 22, 2015, FERC issued an order approving the proposed transaction. The Four Corners transaction closed on July 6, 2016 . See Note D for further details on the sale of Four Corners. Public Service Company of New Mexico ( " PNM " ) Transmission Rate Case. On December 31, 2012, PNM filed with FERC to change its method of transmission rate recovery for its transmission delivery services from stated rates to formula rates. The Company takes transmission service from PNM and is among the PNM transmission customers affected by PNM's shift to formula rates. On March 1, 2013, the FERC issued an order rejecting in part PNM's filing, and establishing settlement judge and hearing procedures. On March 20, 2015, PNM filed with FERC a settlement agreement and offer of settlement resolving all issues set for hearing in the proceeding. On March 25, 2015, the Chief Judge issued an order granting PNM's motion to implement the settled rates. On March 17, 2016, FERC issued an order approving the settlement. Revolving Credit Facility; Issuance of Long-Term Debt and Guarantee of Debt. On October 19, 2015, the FERC issued an order in Docket No. ES15-66-000 approving the Company’s filing to issue short-term debt under its existing revolving credit facility ("RCF") up to $400 million outstanding at any time, to issue up to $310 million in long-term debt, and to guarantee the issuance of up to $65 million of new long-term debt by RGRT to finance future nuclear fuel purchases. The authorization is effective from November 15, 2015 through November 15, 2017 . This approval supersedes prior approvals. Under this authorization, on March 24, 2016 , the Company issued $150 million in aggregate principal amount of 5.00% Senior Notes due December 1, 2044 . The net proceeds from the issuance of these senior notes, after deducting the underwriters' commission, were $158.1 million . These proceeds include accrued interest of $2.4 million and a $7.1 million premium before expenses. These senior notes constitute an additional issuance of the Company's 5.00% Senior Notes due 2044 , of which $150 million was previously issued on December 1, 2014 , for a total principal amount outstanding of $300 million . Other Required Approvals. The Company has obtained required approvals for rates and tariffs, securities transactions and other approvals as required by the FERC.

Palo Verde and Four Corners

Palo Verde and Four Corners	9 Months Ended
	Sep. 30, 2016
Palo Verde and Four Corners [Abstract]
Palo Verde and Four Corners	Palo Verde and Four Corners Spent Nuclear Fuel and Waste Disposal. Pursuant to the Nuclear Waste Policy Act of 1982, as amended in 1987 (the "NWPA"), the U.S. Department of Energy (the "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 (the "Standard Contract") with each nuclear power plant. The DOE failed to begin accepting spent nuclear fuel by 1998. On December 19, 2012 , APS, acting on behalf of itself and the Palo Verde Participants, filed a second breach of contract lawsuit against the DOE. This lawsuit sought to recover damages incurred due to the DOE's failure to accept Palo Verde's spent nuclear fuel for the period beginning January 1, 2007 through June 30, 2011 . On August 18, 2014 , APS and the DOE entered into a settlement agreement, stipulating to a dismissal of the lawsuit and payment of $57.4 million by the DOE to the Palo Verde Participants for certain specified costs incurred by Palo Verde during the period January 1, 2007 through June 30, 2011 . On October 8, 2014 , the Company received approximately $9.1 million , representing its share of the award, of which $7.9 million was credited to customers through the applicable fuel adjustment clauses. On October 31, 2014 , APS, acting on behalf of itself and the Palo Verde Participants, submitted to the government an additional 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. Thereafter, 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. Funds related to this claim were received in the first quarter of 2016 . The Company's share of this claim is approximately $1.9 million , of which $1.6 million was credited to customers through the applicable fuel adjustment clauses in March 2016. On October 31, 2016 , APS filed an $11.3 million claim for the period July 1, 2015 through June 30, 2016 . The Company's share of this claim is approximately $1.8 million . Any reimbursement is anticipated to be received in the second quarter of 2017, and the majority will be 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): 2016 2015 Three months ended September 30, $ 21,123 $ 22,016 Nine months ended September 30, 67,514 67,702 Twelve months ended September 30, 97,451 98,884 Four Corners. On February 17, 2015 , the Company and APS entered into the Purchase and Sale Agreement providing for the purchase by APS of the Company’s interests in Four Corners. Four Corners continued to provide energy to serve the Company's native load up to the closing date. The Four Corners transaction closed on July 6, 2016 . The sales price was $32.0 million based on the net book value as defined in the Purchase and Sale Agreement. The sales price was adjusted downward by $7.0 million and $19.5 million , respectively, to reflect APS's assumption of the Company's obligation to pay for future plant decommissioning and mine reclamation expenses. The sales price was also adjusted downward by approximately $1.3 million for estimated closing adjustments and other assets and liabilities assumed by APS. At the closing, the Company received approximately $4.2 million in cash, subject to post-closing adjustments. No significant gain or loss was recorded upon the closing of the sale. APS assumed responsibility for all capital expenditures made after July 6, 2016 . In addition, APS will indemnify the Company against liabilities and costs related to the future operation of Four Corners. Subsequently, the Company recorded post-closing adjustments to reflect adjustments to estimated capital expenditures and other assets and liabilities assumed by APS through July 6, 2016, which resulted in a $ 1.6 million refund due to APS. See Note C for a discussion of regulatory filings associated with Four Corners.

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2016
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 $12.5 million and $11.9 million in quarterly cash dividends during the three months ended September 30, 2016 and 2015 , respectively. The Company paid a total of $37.0 million and $49.0 million in quarterly cash dividends during the nine and twelve months ended September 30, 2016 , respectively. The Company paid a total of $35.1 million and $46.4 million in quarterly cash dividends during the nine and twelve months ended September 30, 2015 , respectively. 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 September 30, 2016 2015 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,363,819 40,289,010 Dilutive effect of unvested performance awards 62,123 40,519 Diluted number of common shares outstanding 40,425,942 40,329,529 Basic net income per common share: Net income $ 74,636 $ 56,740 Income allocated to participating restricted stock (232 ) (184 ) Net income available to common shareholders $ 74,404 $ 56,556 Diluted net income per common share: Net income $ 74,636 $ 56,740 Income reallocated to participating restricted stock (232 ) (184 ) Net income available to common shareholders $ 74,404 $ 56,556 Basic net income per common share: Distributed earnings $ 0.310 $ 0.295 Undistributed earnings 1.530 1.105 Basic net income per common share $ 1.840 $ 1.400 Diluted net income per common share: Distributed earnings $ 0.310 $ 0.295 Undistributed earnings 1.530 1.105 Diluted net income per common share $ 1.840 $ 1.400 Nine Months Ended September 30, 2016 2015 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,344,834 40,267,533 Dilutive effect of unvested performance awards 50,977 32,268 Diluted number of common shares outstanding 40,395,811 40,299,801 Basic net income per common share: Net income $ 91,112 $ 81,270 Income allocated to participating restricted stock (271 ) (253 ) Net income available to common shareholders $ 90,841 $ 81,017 Diluted net income per common share: Net income $ 91,112 $ 81,270 Income reallocated to participating restricted stock (271 ) (253 ) Net income available to common shareholders $ 90,841 $ 81,017 Basic net income per common share: Distributed earnings $ 0.915 $ 0.870 Undistributed earnings 1.335 1.140 Basic net income per common share $ 2.250 $ 2.010 Diluted net income per common share: Distributed earnings $ 0.915 $ 0.870 Undistributed earnings 1.335 1.140 Diluted net income per common share $ 2.250 $ 2.010 Twelve Months Ended September 30, 2016 2015 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,332,835 40,255,439 Dilutive effect of unvested performance awards 47,608 24,201 Diluted number of common shares outstanding 40,380,443 40,279,640 Basic net income per common share: Net income $ 91,760 $ 85,511 Income allocated to participating restricted stock (264 ) (265 ) Net income available to common shareholders $ 91,496 $ 85,246 Diluted net income per common share: Net income $ 91,760 $ 85,511 Income reallocated to participating restricted stock (264 ) (265 ) Net income available to common shareholders $ 91,496 $ 85,246 Basic net income per common share: Distributed earnings $ 1.21 $ 1.15 Undistributed earnings 1.06 0.97 Basic net income per common share $ 2.27 $ 2.12 Diluted net income per common share: Distributed earnings $ 1.21 $ 1.15 Undistributed earnings 1.06 0.97 Diluted net income per common share $ 2.27 $ 2.12 The amount 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 Nine months ended Twelve Months Ended September 30, September 30, September 30, 2016 2015 2016 2015 2016 2015 Restricted stock awards 57,633 65,076 53,285 60,647 50,854 60,742 Performance shares (a) 62,995 59,898 62,995 59,898 62,995 63,111 (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	9 Months Ended
	Sep. 30, 2016
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 and New Mexico jurisdictions for years prior to 2011 . The Company is currently under audit in Texas for tax years 2007 through 2011 . In June 2016, the Arizona Department of Revenue discontinued their audits for tax years 2009 through 2012 . The discontinuance of the audits did not have a material impact on the Company's results of operations or financial position. For the three months ended September 30, 2016 and 2015 , the Company’s effective tax rate was 36.6% and 30.2% , respectively. For the nine months ended September 30, 2016 and 2015 , the Company's effective tax rate was 36.1% and 30.2% , respectively. For the twelve months ended September 30, 2016 and 2015 , the Company's effective tax rate was 35.8% and 30.4% , 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 Company's regulators in its most recent final orders from the PUCT and the NMPRC. 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 $2.8 million for the three months ended September 30, 2016 . In November 2015, the FASB issued new guidance (ASU 2015-17, Balance Sheet Classification of Deferred Taxes) to simplify the presentation of deferred income taxes. ASU 2015-17 requires that deferred tax liabilities and assets be classified as noncurrent in a classified statement of financial position. ASU 2015-17 can be applied prospectively or retrospectively and is effective for financial statements issued for annual periods beginning after December 15, 2016 and interim periods within those annual periods and early adoption is permitted. The Company elected to implement ASU 2015-17 on a retrospective basis for financial statements issued beginning March 31, 2016. The implementation of ASU 2015-17 did not have a material impact on the Company's results of operations. The impact of ASU 2015-17 on the Company's Balance Sheet was to reclassify $21.6 million of current deferred tax assets to long-term deferred tax liabilities at December 31, 2015. FASB guidance prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. The Company recorded a reduction in the unrecognized tax position of $0.9 million in the three months ended September 30, 2016 , and $0.1 million in the first quarter of 2015 , related to transmission and distribution costs and other amounts deducted in prior year Texas franchise tax returns. The Company recorded a decrease of $0.3 million in the first quarter of 2016 related to tax credits taken and apportionment factors used in prior year Arizona income tax returns, which have been settled through audit. A reconciliation of the September 30, 2016 and 2015 amounts of unrecognized tax benefits are as follows (in thousands): 2016 2015 Balance at January 1 $ 6,000 $ 5,200 Additions for tax position related to the current year — — Reductions for tax positions related to the current year — — Additions for tax positions of prior years — — Reductions for tax positions (1,200 ) (100 ) Balance at September 30 $ 4,800 $ 5,100

Commitments, Contingencies And

Commitments, Contingencies And Uncertainties	9 Months Ended
	Sep. 30, 2016
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 2015 Form 10-K. In addition, see Notes C and D above and Notes C and E of the Notes to Financial Statements in the 2015 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 2015 Form 10-K. Environmental Matters General. The Company is subject to extensive laws, regulations, and permit requirements with respect to air and greenhouse gas 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. For a more detailed discussion of certain key environmental issues, laws, and regulations facing the Company, see Note K of the Notes to Financial Statements in the 2015 Form 10-K. Clean Air Interstate Rule/Cross State Air Pollution Rule . The EPA promulgated the Cross-State Air Pollution Rule ("CSAPR") in August 2011, which rule involves requirements to limit emissions of nitrogen oxides ("NOx") and sulfur dioxide ("SO2") from certain of the Company's power plants in Texas and/or purchase allowances representing other parties' emissions reductions. CSAPR was intended to replace the EPA's 2005 Clean Air Interstate Rule ("CAIR"). While the U.S. Court of Appeals for the District of Columbia Circuit ("D.C. Circuit") vacated CSAPR in August 2012 and allowed CAIR to stand until the EPA issued a proper replacement, on April 29, 2014, the U.S. Supreme Court reversed and upheld CSAPR, remanding certain portions of CSAPR to the D.C. Circuit for further consideration. On June 26, 2014, the EPA filed a motion asking the D.C. Circuit to lift its stay on CSAPR, and on October 23, 2014, the D.C Circuit lifted its stay of CSAPR. On July 28, 2015, the D.C. Circuit ruled that the EPA's emissions budgets for 13 states including Texas are invalid, but left the rule in place on remand. On October 26, 2016, the EPA published its final CSAPR Update Rule with an effective date of December 27, 2016. While we are unable to determine the full impact of this rule at this time, the Company believes it is currently positioned to comply with CSAPR. National Ambient Air Quality Standards ("NAAQS"). Under the Clean Air Act ("CAA"), the EPA sets NAAQS for six criteria pollutants considered harmful to public health and the environment, including particulate matter ("PM"), NOx, carbon monoxide ("CO"), ozone, and SO2. NAAQS must be reviewed by the EPA at five -year intervals. In 2010, the EPA tightened the NAAQS for both nitrogen dioxide ("NO2") and SO2. The EPA is considering a 1-hour secondary NAAQS for NO2 and SO2. In January 2013, the EPA tightened the NAAQS for fine PM. On October 1, 2015, following on its November 2014 proposal, the EPA released a final rule tightening the primary and secondary NAAQS for ground-level ozone from its 2008 standard levels of 75 parts per billion ("ppb") to 70 ppb. Ozone is the main component of smog. While not directly emitted into the air, it forms from precursors, including NOx and volatile organic compounds, in combination with sunlight. The EPA is expected to make attainment/nonattainment designations for the revised ozone standards by October 1, 2017. While it is currently unknown how the areas in which we operate will ultimately be designated, for nonattainment areas classified as "Moderate" and above, states, and any tribes that choose to do so, are expected to be required to complete development of implementation plans in the 2020-2021 timeframe. Most nonattainment areas are expected to have until 2020 or 2023 to meet the primary (health) standard, with the exact attainment date varying based on the ozone level in the area. The Company continues to evaluate what impact these final and proposed NAAQS could have on its operations. If the Company is required to install additional equipment to control emissions at its facilities, the NAAQS, individually or in the aggregate, could have a material impact on its operations and financial results. Other Laws and Regulations and Risks. The Company sold its interest in Four Corners to APS on July 6, 2016 . The Company no longer owns any coal-fired generation, and therefore has reduced its exposure to a number of environmental matters. As of the closing date of the sale, the Company's environmental liabilities associated with Four Corners were limited to conditions that existed at the time of the sale. The Company's liability is limited to the portion thereof for which the Company would have been financially responsible if Four Corners had fully ceased operations on July 6, 2016 . The Company believes it is not responsible for a significant portion of the compliance or ongoing operational costs associated with the Mercury and Air Toxics Standards ("MATS"), the Coal Combustion Residue ("CCR") Rule, or the revised Wastewater Effluent Limitation Guidelines ("ELG"). While the outcome of these matters cannot be predicted with certainty, the Company does not expect the MATS, CCR, or ELG rules to have a significant impact on its financial condition or results of operations, nor does the Company expect that ongoing lawsuits between environmental organizations, the Office of Surface Mining Reclamation and Enforcement, the Bureau of Indian Affairs, and other federal agencies will have a significant impact on its financial condition or results of operations. Mercury and Air Toxics Standards. The operation of coal-fired power plants, such as Four Corners, results in emissions of mercury and other air toxics. In December 2011, the EPA finalized the MATS Rule for oil- and coal-fired power plants, which requires significant reductions in emissions of mercury and other air toxics. Several judicial and other challenges have been made to this rule, and on June 29, 2015, the U.S. Supreme Court remanded the rule to the D.C. Circuit Court. On December 15, 2015, the D.C. Circuit Court issued an order remanding the rule to the EPA but did not vacate the rule during remand. On April 15, 2016, the EPA completed a cost-benefit analysis of the MATS rule and reaffirmed its finding that the rule is "appropriate and necessary," which will be reviewed by the D.C. Circuit Court. The legal status of the MATS Rule notwithstanding, the Company believes, under the terms of the Purchase and Sale Agreement and after the sale, as a former owner, that the Company is not responsible for a significant portion of the costs under the MATS Rule. Accordingly, the Company does not expect the MATS Rule to have a significant impact on its financial condition or results of operations. Coal Combustion Waste. On October 19, 2015, the EPA's final rule regulating the disposal of CCR (the "CCR Rule") from electric utilities as solid waste took effect. As of the effective date of the CCR Rule, the Company had a 7% ownership interest in Units 4 and 5 of Four Corners, the only coal-fired generating facility for which the Company had an ownership interest subject to the CCR Rule. The Company sold its entire ownership interest in Four Corners to APS on July 6, 2016 . The CCR Rule requires plant owners to treat coal combustion residuals as Subtitle D (as opposed to a more costly Subtitle C) waste. The Company, however, believes, under the terms of the Purchase Agreement and after the sale, as a former owner, that the Company is not responsible for a significant portion of the costs under the CCR Rule, such as ongoing operational costs after July 6, 2016 . Accordingly, the Company does not expect the CCR Rule to have a significant impact on its financial condition or results of operations. On November 3, 2015, the EPA published a final rule revising wastewater effluent limitation guidelines for steam electric power generators (the "Revised ELG Rule"). The Revised ELG Rule establishes requirements for wastewater streams from certain processes at affected facilities, including limits on toxic metals in wastewater discharges. Facilities must comply with the Revised ELG Rule between 2018 and 2023. The EPA anticipates that the new requirements in the Revised ELG Rule will only affect certain coal-fired steam electric power plants. Because the Company does not have an interest in Four Corners after the closing of the sale in July 2016 , the Company does not expect the Revised ELG Rule will have a significant impact on its financial condition or results of operations. In 2012, several environmental groups filed a lawsuit in federal district court against the Office of Surface Mining Reclamation and Enforcement ("OSM") of the U.S. Department of the Interior, challenging OSM’s 2012 approval of a permit revision which allowed for the expansion of mining operations into a new area of the mine that serves Four Corners ("Area IV North"). In April 2015, the court issued an order invalidating the permit revision, thereby prohibiting mining in Area IV North until OSM takes action to cure the defect in its permitting process identified by the court. On December 29, 2015, OSM took action to cure the defect in its permitting process by issuing a revised environmental assessment and finding of no new significant impact, and reissued the permit. This action is subject to possible judicial review. On March 30, 2016, the U.S. Court of Appeals vacated and dismissed the federal court decision that halted operations in Area IV North at the Navajo Mine. On April 20, 2016, the same environmental groups filed a new complaint in Arizona's federal district court, challenging multiple permits and approvals issued to both the Navajo Mine and Four Corners authorizing operations from July 2016 onwards. The complaint seeks to enjoin federal agencies, including the OSM and Bureau of Indian Affairs, from authorizing any element of the power plant or mine without further environmental impact analysis. Climate Change. In recent years, there has been increasing public debate regarding the potential impact of global climate change. There has been a wide-ranging policy debate, both nationally and internationally, regarding the impact of GHG and possible means for their regulation. In addition, efforts have been made and continue to be made in the international community toward the adoption of international treaties or protocols that would address global climate change issues. Most recently, in 2015, the United States participated in the United Nations Conference on Climate Change, which led to creation of the Paris Agreement. On April 22, 2016, 175 countries, including the United States, signed the Paris Agreement, signaling their intent to join. Those countries that subsequently ratify the agreement will be required to review and "represent a progression" in their intended nationally determined contributions, which set GHG emission reduction goals, every five years, beginning in 2020. The U.S. federal government has either considered, proposed, and/or finalized legislation or regulations limiting GHG emissions, including carbon dioxide. In particular, the U.S. Congress has considered legislation to restrict or regulate GHG emissions. In the past few years, the EPA began using the CAA to regulate carbon dioxide and other GHG emissions, such as the 2009 GHG Reporting Rule and the EPA's sulfur hexafluoride ("SF6") reporting rule, both of which apply to the Company, as well as the EPA's 2010 actions to impose permitting requirements on new and modified sources of GHG emissions. After announcing his plan to address climate change in 2013, the President directed the EPA to issue proposals for GHG rulemaking addressing power plants. In October 2015, the EPA published a final rule establishing new source performance standards ("NSPS") limiting CO2 emissions from new, modified, and reconstructed electric generating units. In October 2015, the EPA also published a rule establishing guidelines for states to regulate CO2 emissions from existing power plants, as well as a proposed "federal plan" to address CO2 emissions from affected units in those states that do not submit an approvable compliance plan. The standards for existing plants are known as the Clean Power Plan ("CPP"), under which rule interim emissions performance rates must be achieved beginning in 2022 and final emissions performance rates by 2030. Legal challenges to the CPP were filed by groups of states and industry members. On February 9, 2016, the U.S. Supreme Court issued a decision to stay the rule until legal issues are resolved. We cannot at this time determine the impact the CPP and related rules and legal challenges may have on our financial position, results of operations, or cash flows.

Litigation

Litigation	9 Months Ended
	Sep. 30, 2016
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 2015 Form 10-K for discussion of the effects of government legislation and regulation on the Company.

Employee Benefits

Employee Benefits	9 Months Ended
	Sep. 30, 2016
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Employee Benefits	Employee Benefits Retirement Plans The net periodic benefit cost recognized for the three, nine and twelve months ended September 30, 2016 and 2015 is made up of the components listed below as determined using the projected unit credit actuarial cost method (in thousands): Three Months Ended Nine Months Ended Twelve Months Ended September 30, September 30, September 30, 2016 2015 2016 2015 2016 2015 Components of net periodic benefit cost: Service cost $ 2,191 $ 2,394 $ 6,001 $ 6,594 $ 8,199 $ 8,707 Interest cost 3,250 3,622 9,780 10,872 13,403 14,563 Expected return on plan assets (4,734 ) (4,951 ) (14,159 ) (14,846 ) (19,108 ) (19,528 ) Amortization of: Net loss 1,730 2,485 5,505 7,985 8,167 10,267 Prior service benefit (875 ) (855 ) (2,630 ) (2,630 ) (3,506 ) (3,506 ) Net periodic benefit cost $ 1,562 $ 2,695 $ 4,497 $ 7,975 $ 7,155 $ 10,503 During the nine months ended September 30, 2016 , the Company contributed $8.8 million of its projected $9.4 million 2016 annual contribution to its retirement plans. Other Postretirement Benefits The net periodic benefit cost recognized for the three, nine and twelve months ended September 30, 2016 and 2015 is made up of the components listed below (in thousands): Three Months Ended Nine Months Ended Twelve Months Ended September 30, September 30, September 30, 2016 2015 2016 2015 2016 2015 Components of net periodic benefit cost: Service cost $ 749 $ 841 $ 2,179 $ 2,591 $ 3,042 $ 3,302 Interest cost 871 976 2,616 3,026 3,625 4,142 Expected return on plan assets (452 ) (503 ) (1,372 ) (1,553 ) (1,889 ) (2,082 ) Amortization of: Prior service benefit (788 ) (751 ) (2,363 ) (2,301 ) (3,130 ) (3,490 ) Net gain (643 ) (519 ) (1,973 ) (1,519 ) (2,479 ) (2,186 ) Net periodic benefit cost (benefit) $ (263 ) $ 44 $ (913 ) $ 244 $ (831 ) $ (314 ) During the nine months ended September 30, 2016 , the Company contributed $1.6 million of its projected $1.7 million 2016 annual contribution to its other post retirement benefits plan. During October 2016, the Company approved and communicated a plan amendment that is expected to result in a remeasurement. Effective January 1, 2017, retirees and dependents that are less than 65 years of age will be offered a choice between a $1,000 and $2,250 deductible plan. Additionally, retirees and dependents that are 65 years of age or greater will be covered by a fully insured Medicare advantage plan. The postretirement benefit obligation is estimated to decrease by approximately $32.7 million as a result of the October 1, 2016 remeasurement. The effects of the remeasurement will be recorded in the fourth quarter of 2016.

Financial Instruments And Inves

Financial Instruments And Investments (Notes)	9 Months Ended
	Sep. 30, 2016
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 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): September 30, 2016 December 31, 2015 Carrying Amount (1) Estimated Fair Value Carrying Amount (1) Estimated Fair Value Pollution Control Bonds $ 190,706 $ 211,050 $ 190,499 $ 212,624 Senior Notes 993,004 1,207,162 837,475 829,864 RGRT Senior Notes (2) 94,768 100,465 94,686 100,345 RCF (2) 55,192 55,192 141,738 141,738 Total $ 1,333,670 $ 1,573,869 $ 1,264,398 $ 1,284,571 _______________ (1) The Company implemented ASU 2015-03, Interest - Imputation of Interest, which requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability. ASU 2015-03 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. The impact of ASU 2015-03 on the Company's Balance Sheet was to reclassify $11.6 million of other deferred charges to long-term debt, net of current portion at December 31, 2015. (2) Nuclear fuel financing, as of September 30, 2016 and December 31, 2015 , is funded through the $95 million RGRT Senior Notes and $36.2 million and $33.7 million , respectively under the RCF. As of September 30, 2016 , $19.0 million was outstanding under the RCF for working capital or general corporate purposes. As of December 31, 2015 , $108.0 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 $254.6 million and $239.0 million at September 30, 2016 and December 31, 2015 , 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): September 30, 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 (1) : Federal Agency Mortgage Backed Securities $ 1,028 $ (9 ) $ — $ — $ 1,028 $ (9 ) U.S. Government Bonds 8,728 (151 ) 12,300 (526 ) 21,028 (677 ) Municipal Obligations 4,692 (43 ) 8,171 (515 ) 12,863 (558 ) Corporate Obligations 3,380 (50 ) 2,381 (138 ) 5,761 (188 ) Total Debt Securities 17,828 (253 ) 22,852 (1,179 ) 40,680 (1,432 ) Common Stock 1,393 (124 ) — — 1,393 (124 ) Institutional Equity Funds-International Equity 22,847 (249 ) — — 22,847 (249 ) Total Temporarily Impaired Securities $ 42,068 $ (626 ) $ 22,852 $ (1,179 ) $ 64,920 $ (1,805 ) _________________ (1) Includes 104 securities. December 31, 2015 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 $ 9,383 $ (97 ) $ 1,113 $ (47 ) $ 10,496 $ (144 ) U.S. Government Bonds 24,094 (310 ) 14,272 (623 ) 38,366 (933 ) Municipal Obligations 8,286 (160 ) 7,388 (446 ) 15,674 (606 ) Corporate Obligations 6,058 (722 ) 2,307 (228 ) 8,365 (950 ) Total Debt Securities 47,821 (1,289 ) 25,080 (1,344 ) 72,901 (2,633 ) Common Stock 3,584 (344 ) — — 3,584 (344 ) Institutional Equity Funds-International Equity 22,454 (768 ) — — 22,454 (768 ) Total Temporarily Impaired Securities $ 73,859 $ (2,401 ) $ 25,080 $ (1,344 ) $ 98,939 $ (3,745 ) _________________ (2) Includes 133 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, nine and twelve months ended September 30, 2016 and 2015 , the Company recognized other than temporary impairment losses on its available-for-sale securities as follow (in thousands): Three Months Ended Nine Months Ended Twelve Months Ended September 30, September 30, September 30, 2016 2015 2016 2015 2016 2015 Unrealized holding losses included in pre-tax income $ (196 ) $ — $ (352 ) $ — $ (690 ) $ — 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): September 30, 2016 December 31, 2015 Fair Value Unrealized Gains Fair Value Unrealized Gains Description of Securities: Federal Agency Mortgage Backed Securities $ 16,772 $ 701 $ 9,589 $ 438 U.S. Government Bonds 35,711 1,285 12,033 136 Municipal Obligations 9,273 398 8,671 332 Corporate Obligations 18,368 1,347 10,110 368 Total Debt Securities 80,124 3,731 40,403 1,274 Common Stock 66,055 34,418 72,636 37,001 Equity Mutual Funds 35,552 1,995 18,853 91 Cash and Cash Equivalents 7,975 — 8,204 — Total $ 189,706 $ 40,144 $ 140,096 $ 38,366 The Company's marketable securities include investments in municipal, corporate and federal debt obligations. Substantially all of the Company's mortgage-backed securities, based on contractual maturity, are due in ten years or more. The mortgage-backed securities have an estimated weighted average maturity which generally range from two years to six years and reflects anticipated future prepayments. The contractual year for maturity of these available-for-sale securities as of September 30, 2016 is as follows (in thousands): Total 2016 2017 2021 through 2025 2026 and Beyond Municipal Debt Obligations $ 22,136 $ 417 $ 7,909 $ 12,730 $ 1,080 Corporate Debt Obligations 24,129 — 5,501 9,941 8,687 U.S. Government Bonds 56,739 — 29,297 14,542 12,900 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, nine, and twelve months ended September 30, 2016 and 2015 and the related effects on pre-tax income are as follows (in thousands): Three Months Ended Nine Months Ended Twelve Months Ended September 30, September 30, September 30, 2016 2015 2016 2015 2016 2015 Proceeds from sales or maturities of available-for-sale securities $ 19,453 $ 26,618 $ 60,165 $ 63,776 $ 98,956 $ 124,732 Gross realized gains included in pre-tax income $ 2,446 $ 4,515 $ 6,687 $ 8,330 $ 10,736 $ 12,467 Gross realized losses included in pre-tax income (178 ) (191 ) (765 ) (443 ) (1,249 ) (1,021 ) Gross unrealized losses included in pre-tax income (196 ) — (352 ) — (690 ) — Net gains included in pre-tax income $ 2,072 $ 4,324 $ 5,570 $ 7,887 $ 8,797 $ 11,446 Net unrealized holding gains (losses) included in accumulated other comprehensive income $ 4,313 $ (8,092 ) $ 9,293 $ (8,641 ) $ 15,028 $ (5,779 ) Net gains reclassified from accumulated other comprehensive income (2,072 ) (4,324 ) (5,570 ) (7,887 ) (8,797 ) (11,446 ) Net gains (losses) in other comprehensive income $ 2,241 $ (12,416 ) $ 3,723 $ (16,528 ) $ 6,231 $ (17,225 ) 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 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 re-evaluated the decommissioning trust funds investments as to whether they have a readily determinable fair value. Based on that re-evaluation, certain accounting policy, and NAV disclosures have been revised and now the investments in the Institutional Funds are categorized as Level 1. • 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 September 30, 2016 and December 31, 2015 , 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 September 30, 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 $ 1,398 $ — $ — $ 1,398 Available for sale: U.S. Government Bonds $ 56,739 $ 56,739 $ — $ — Federal Agency Mortgage Backed Securities 17,800 — 17,800 — Municipal Bonds 22,136 — 22,136 — Corporate Asset Backed Obligations 24,129 — 24,129 — Subtotal Debt Securities 120,804 56,739 64,065 — Common Stock 67,448 67,448 — — Equity Mutual Funds 35,552 35,552 — — Institutional Funds-International Equity 22,847 22,847 — — Cash and Cash Equivalents 7,975 7,975 — — Total Available for Sale $ 254,626 $ 190,561 $ 64,065 $ — Description of Securities Fair Value as of December 31, 2015 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 $ 1,543 $ — $ — $ 1,543 Available for sale: U.S. Government Bonds $ 50,399 $ 50,399 $ — $ — Federal Agency Mortgage Backed Securities 20,085 — 20,085 — Municipal Bonds 24,345 — 24,345 — Corporate Asset Backed Obligations 18,475 — 18,475 — Subtotal Debt Securities 113,304 50,399 62,905 — Common Stock 76,220 76,220 — — Equity Mutual Funds 18,853 18,853 — — Institutional Funds-International Equity 22,454 22,454 — — Cash and Cash Equivalents 8,204 8,204 — — Total Available for Sale $ 239,035 $ 176,130 $ 62,905 $ — 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, nine and twelve month periods ended September 30, 2016 and 2015 . There were no purchases, sales, issuances, and settlements related to the assets in the Level 3 fair value measurement category during the three, nine and twelve months ended September 30, 2016 and 2015 .

Principles Of Preparation (Poli

Principles Of Preparation (Policy)	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
Use of Estimates, Policy	Use of Estimates . The preparation of financial statements in conformity with generally accepted accounting principles 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 $30.3 million at September 30, 2016 and $21.7 million at December 31, 2015 . 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. Based, in part, upon a 2014 study performed for the Company, the Company modified certain salvage values related to both interim and final removal costs and service lives which were approved by the Company's regulators in 2016. The effect of the change in these estimates resulted in reducing depreciation expense approximately $7.4 million for the nine months ended September 30, 2016. The Company expects that the 2016 annual reduction to depreciation expense to approximate $9.5 million .
Income Tax, Policy	Income Taxes . The Company accounts for federal and state income taxes under the asset and liability method of accounting for income taxes. Deferred income taxes are recognized for the estimated future tax consequences of "temporary differences" by applying enacted statutory tax rates for each taxable jurisdiction applicable to future years to differences between the financial statement carrying amounts and the tax basis of existing assets and liabilities. Historically, certain temporary differences are accorded flow-through treatment by the Company's regulators and impact the Company's effective tax rate. The Financial Accounting Standards Board ("FASB") guidance requires that rate-regulated companies record deferred income taxes for temporary differences accorded flow-through treatment at the direction of the regulatory commission. The resulting deferred tax assets and liabilities are recorded at the expected cash flow to be reflected in future rates. Because the Company's regulators have consistently permitted the recovery of tax effects previously flowed-through earnings, the Company has recorded regulatory liabilities and assets offsetting such deferred tax assets and liabilities. During 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 Company's regulators in its most recent final orders from the Public Utility Commission of Texas ("PUCT") and the New Mexico Public Regulation Commission ("NMPRC"). Accordingly, the Company recorded deferred state income tax expense as required by normalization, retroactive to January 2016 as provided in the final orders. See Note F for further discussion. The effect on deferred tax assets and liabilities of a change in tax rate is recognized in income in the period that includes the enactment date. The Company recognizes tax assets and liabilities for uncertain tax positions in accordance with the recognition and measurement criteria of the FASB guidance for uncertainty in income taxes. See Note F.
New Accounting Standards, Policy	New Accounting Standards. In April 2015, the FASB issued Accounting Standards Update ("ASU") 2015-03, Interest - Imputation of Interest (Topic 715) to simplify the presentation of debt issuance costs. ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by this ASU. ASU 2015-03 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. In August 2015, the FASB issued ASU 2015-15, Interest - Imputation of Interest (Subtopic 835-30), to provide further clarification to ASU 2015-03 as it relates to the presentation and subsequent measurement of debt issuance costs associated with line of credit arrangements. The Company implemented ASU 2015-03 and ASU 2015-15 in the first quarter of 2016, retrospectively to all prior periods presented in the Company's Balance Sheet. The implementation of ASU 2015-03 did not have an impact on the Company's results of operations. See Note J. In November 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes to simplify the presentation of deferred income taxes. ASU 2015-17 requires that deferred tax liabilities and assets be classified as noncurrent in a classified statement of financial position. ASU 2015-17 can be applied prospectively or retrospectively and is effective for financial statements issued for annual periods beginning after December 15, 2016 and interim periods within those annual periods and early adoption is permitted . The Company elected to early adopt ASU 2015-17 retrospectively in the first quarter of 2016 in the Company's Balance Sheet. The implementation of ASU 2015-17 did not have an impact on the Company's results of operations. See Note F. 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. ASU 2014-09 is the result of a joint effort by the FASB and the International Accounting Standards Board intended to clarify the principles for recognizing revenue and to develop a common revenue standard for U.S. Generally Accepted Accounting Principles ("GAAP") and International Financial Reporting Standards. ASU 2014-09 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. ASU 2014-09 was originally intended to be effective for annual periods and interim periods within that reporting period beginning after December 15, 2016, for public business entities. In August 2015, FASB issued ASU 2015-14 to defer the effective date of ASU 2014-09 for all entities by one year. Public business entities will apply the guidance in ASU 2014-09 to annual reporting periods beginning after December 15, 2017 and interim periods within that reporting period. In March 2016, the FASB issued ASU 2016-08 to clarify the implementation guidance on principal versus agent consideration. In April 2016, the FASB issued ASU 2016-10 to clarify the implementation guidance on identifying performance obligations and licensing. In May 2016, the FASB issued ASU 2016-11, which rescinds certain SEC Staff Observer comments that are codified in FASB ASC Topic 605 (Revenue Recognition), effective upon adoption of Topic 606. In May 2016, the FASB issued ASU 2016-12, which makes narrow-scope amendments to ASU 2014-09, and provides practical expedients to simplify the transition to the new standard and to clarify certain aspects of the standard. Early adoption of ASU 2014-09 is permitted after December 15, 2016. The Company has not selected a transition method and is currently assessing the future impact of this ASU. 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 standard includes a requirement that businesses must report changes in the fair value of their own liabilities in other comprehensive income instead of earnings, and this is the only provision of the update for which the FASB is permitting early adoption. The remaining provisions of this ASU become effective for public companies for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The Company is currently assessing 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 (the 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. 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 for public companies will be required for annual reporting periods beginning after December 15, 2018 and interim periods within that reporting period. Early adoption of ASU 2016-02 is permitted for all entities. 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 assessing the future impact of this ASU. In March 2016, the FASB issued 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. This ASU is effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods. Early adoption is permitted. The Company is currently assessing the future impact of this ASU. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326). ASU 2016-13 significantly 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. For public business entities, the provisions of ASU 2016-13 are effective for fiscal years and interim periods within that reporting period beginning after December 15, 2019. Early implementation is permitted as of the fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. 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 this ASU. 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 new guidance addresses the following classification issues: debt prepayment or debt extinguishment costs; settlement of zero-coupon bonds; contingent consideration payments made after a business combination; proceeds from the settlement of insurance claims; proceeds from the settlement of corporate-owned life insurance policies, including bank-owned life insurance policies; distributions received from equity method investees; beneficial interests in securitization transactions; and separately identifiable cash flows and application of the predominance principle. For public business entities, the provisions of ASU 2016-15 are effective for fiscal years and interim periods within that reporting period beginning after December 15, 2017. Early adoption is permitted, including adoption in an interim period. If an entity elects early adoption of ASU 2016-15 in an interim period, adjustments should be reflected as of the beginning of the fiscal year that includes that interim period. An entity that elects early adoption must adopt all of the amendments in the same period. 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.
Reclassification, Policy	Reclassification. Certain amounts in the financial statements for 2015 have been reclassified to conform to the 2016 presentation. The Company implemented ASU 2015-03 and ASU 2015-17 in the first quarter of 2016, retrospectively to all periods presented in the Company's financial statements. See Note F and Note J, respectively.

Principles Of Preparation (Tabl

Principles Of Preparation (Tables)	9 Months Ended
	Sep. 30, 2016
Supplemental Cash Flow Information [Abstract]
Cash Flow, Supplemental Disclosures	Supplemental Cash Flow Disclosures (in thousands) Nine Months Ended September 30, 2016 2015 Cash paid (received) for: Interest on long-term debt and borrowings under the revolving credit facility $ 46,867 $ 41,406 Income tax paid (refunded), net 3,337 (272 ) Non-cash investing and financing activities: Sale of Interest in Four Corners Generating Station (a) 27,720 — Changes in accrued plant additions 4,277 (13,150 ) Grants of restricted shares of common stock 1,236 1,106 (a) The Company sold its interest in the Four Corners Generating Station ("Four Corners") for approximately $32.0 million based on the book value as defined in the asset purchase agreement entered into by the Company and Arizona Public Service Company ("APS") on February 17, 2015 (the "Purchase and Sale Agreement"). The sales price was adjusted downward by $7.0 million and $19.5 million , respectively, to reflect APS assumption of the Company's obligation to pay for future plant decommissioning and mine reclamation expense. The sales price was also adjusted downward by approximately $1.3 million for closing adjustments and other assets and liabilities assumed by APS. At the closing of the sale, the Company received approximately $4.2 million in cash, subject to post-closing adjustments. Subsequently, the Company recorded post-closing adjustments to reflect adjustments to estimated capital expenditures and other assets and liabilities assumed by APS through July 6, 2016, which resulted in a $1.6 million refund due to APS.

Accumulated Other Comprehensi20

Accumulated Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2016
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 September 30, 2016 Three Months Ended September 30, 2015 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 (loss) before reclassifications — 3,493 — 3,493 — (6,485 ) — (6,485 ) Amounts reclassified from accumulated other comprehensive income (loss) (804 ) (1,687 ) (39 ) (2,530 ) 226 (3,472 ) 72 (3,174 ) Balance at end of period $ (31,336 ) $ 30,731 $ (11,732 ) $ (12,337 ) $ (34,105 ) $ 25,769 $ (11,887 ) $ (20,223 ) Nine Months Ended September 30, 2016 Nine Months Ended September 30, 2015 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 $ (29,869 ) $ 27,765 $ (11,810 ) $ (13,914 ) $ (34,884 ) $ 38,957 $ (12,074 ) $ (8,001 ) Other comprehensive income (loss) before reclassifications — 7,459 — 7,459 — (6,854 ) — (6,854 ) Amounts reclassified from accumulated other comprehensive income (loss) (1,467 ) (4,493 ) 78 (5,882 ) 779 (6,334 ) 187 (5,368 ) Balance at end of period $ (31,336 ) $ 30,731 $ (11,732 ) $ (12,337 ) $ (34,105 ) $ 25,769 $ (11,887 ) $ (20,223 ) Twelve Months Ended September 30, 2016 Twelve Months Ended September 30, 2015 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 $ (34,105 ) $ 25,769 $ (11,887 ) $ (20,223 ) $ (9,818 ) $ 39,525 $ (12,146 ) $ 17,561 Other comprehensive income (loss) before reclassifications 3,777 12,058 — 15,835 (24,775 ) (4,537 ) — (29,312 ) Amounts reclassified from accumulated other comprehensive income (loss) (1,008 ) (7,096 ) 155 (7,949 ) 488 (9,219 ) 259 (8,472 ) Balance at end of period $ (31,336 ) $ 30,731 $ (11,732 ) $ (12,337 ) $ (34,105 ) $ 25,769 $ (11,887 ) $ (20,223 )
Reclassification out of Accumulated Other Comprehensive Income	Amounts reclassified from Accumulated Other Comprehensive Income (Loss) for the three, nine and twelve months ended September 30, 2016 and 2015 are as follows (in thousands): Details about Accumulated Other Comprehensive Income (Loss) Components Three Months Ended September 30, Nine Months Ended September 30, Twelve Months Ended September 30, Affected Line Item in the Statement of Operations 2016 2015 2016 2015 2016 2015 Amortization of pension and post-retirement benefit costs: Prior service benefit $ 1,663 $ 1,606 $ 4,993 $ 4,931 $ 6,636 $ 6,996 (a) Net loss (1,087 ) (1,966 ) (3,532 ) (6,466 ) (5,688 ) (8,081 ) (a) 576 (360 ) 1,461 (1,535 ) 948 (1,085 ) (a) Income tax effect 228 134 6 756 60 597 Income tax expense 804 (226 ) 1,467 (779 ) 1,008 (488 ) (a) Marketable securities: Net realized gain on sale of securities 2,072 4,324 5,570 7,887 8,797 11,446 Investment and interest income, net 2,072 4,324 5,570 7,887 8,797 11,446 Income before income taxes Income tax effect (385 ) (852 ) (1,077 ) (1,553 ) (1,701 ) (2,227 ) Income tax expense 1,687 3,472 4,493 6,334 7,096 9,219 Net income Loss on cash flow hedge: Amortization of loss (126 ) (118 ) (371 ) (348 ) (490 ) (460 ) Interest on long-term debt and revolving credit facility (126 ) (118 ) (371 ) (348 ) (490 ) (460 ) Income before income taxes Income tax effect 165 46 293 161 335 201 Income tax expense 39 (72 ) (78 ) (187 ) (155 ) (259 ) Net income Total reclassifications $ 2,530 $ 3,174 $ 5,882 $ 5,368 $ 7,949 $ 8,472 (a) These items are included in the computation of net periodic benefit cost. See Note I, Employee Benefits, for additional information.

Palo Verde and Four Corners (Ta

Palo Verde and Four Corners (Tables)	9 Months Ended
	Sep. 30, 2016
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): 2016 2015 Three months ended September 30, $ 21,123 $ 22,016 Nine months ended September 30, 67,514 67,702 Twelve months ended September 30, 97,451 98,884

Common Stock (Tables)

Common Stock (Tables)	9 Months Ended
	Sep. 30, 2016
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 September 30, 2016 2015 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,363,819 40,289,010 Dilutive effect of unvested performance awards 62,123 40,519 Diluted number of common shares outstanding 40,425,942 40,329,529 Basic net income per common share: Net income $ 74,636 $ 56,740 Income allocated to participating restricted stock (232 ) (184 ) Net income available to common shareholders $ 74,404 $ 56,556 Diluted net income per common share: Net income $ 74,636 $ 56,740 Income reallocated to participating restricted stock (232 ) (184 ) Net income available to common shareholders $ 74,404 $ 56,556 Basic net income per common share: Distributed earnings $ 0.310 $ 0.295 Undistributed earnings 1.530 1.105 Basic net income per common share $ 1.840 $ 1.400 Diluted net income per common share: Distributed earnings $ 0.310 $ 0.295 Undistributed earnings 1.530 1.105 Diluted net income per common share $ 1.840 $ 1.400 Nine Months Ended September 30, 2016 2015 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,344,834 40,267,533 Dilutive effect of unvested performance awards 50,977 32,268 Diluted number of common shares outstanding 40,395,811 40,299,801 Basic net income per common share: Net income $ 91,112 $ 81,270 Income allocated to participating restricted stock (271 ) (253 ) Net income available to common shareholders $ 90,841 $ 81,017 Diluted net income per common share: Net income $ 91,112 $ 81,270 Income reallocated to participating restricted stock (271 ) (253 ) Net income available to common shareholders $ 90,841 $ 81,017 Basic net income per common share: Distributed earnings $ 0.915 $ 0.870 Undistributed earnings 1.335 1.140 Basic net income per common share $ 2.250 $ 2.010 Diluted net income per common share: Distributed earnings $ 0.915 $ 0.870 Undistributed earnings 1.335 1.140 Diluted net income per common share $ 2.250 $ 2.010 Twelve Months Ended September 30, 2016 2015 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,332,835 40,255,439 Dilutive effect of unvested performance awards 47,608 24,201 Diluted number of common shares outstanding 40,380,443 40,279,640 Basic net income per common share: Net income $ 91,760 $ 85,511 Income allocated to participating restricted stock (264 ) (265 ) Net income available to common shareholders $ 91,496 $ 85,246 Diluted net income per common share: Net income $ 91,760 $ 85,511 Income reallocated to participating restricted stock (264 ) (265 ) Net income available to common shareholders $ 91,496 $ 85,246 Basic net income per common share: Distributed earnings $ 1.21 $ 1.15 Undistributed earnings 1.06 0.97 Basic net income per common share $ 2.27 $ 2.12 Diluted net income per common share: Distributed earnings $ 1.21 $ 1.15 Undistributed earnings 1.06 0.97 Diluted net income per common share $ 2.27 $ 2.12
Schedule of Antidilutive Securities Excluded From Computation Of Earnings Per Share	The amount 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 Nine months ended Twelve Months Ended September 30, September 30, September 30, 2016 2015 2016 2015 2016 2015 Restricted stock awards 57,633 65,076 53,285 60,647 50,854 60,742 Performance shares (a) 62,995 59,898 62,995 59,898 62,995 63,111 (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 (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2016
Income Taxes [Abstract]
Summary of Income Tax Contingencies [Table Text Block]	A reconciliation of the September 30, 2016 and 2015 amounts of unrecognized tax benefits are as follows (in thousands): 2016 2015 Balance at January 1 $ 6,000 $ 5,200 Additions for tax position related to the current year — — Reductions for tax positions related to the current year — — Additions for tax positions of prior years — — Reductions for tax positions (1,200 ) (100 ) Balance at September 30 $ 4,800 $ 5,100

Employee Benefits (Tables)

Employee Benefits (Tables)	9 Months Ended
	Sep. 30, 2016
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Schedule of Net Benefit Costs	The net periodic benefit cost recognized for the three, nine and twelve months ended September 30, 2016 and 2015 is made up of the components listed below as determined using the projected unit credit actuarial cost method (in thousands): Three Months Ended Nine Months Ended Twelve Months Ended September 30, September 30, September 30, 2016 2015 2016 2015 2016 2015 Components of net periodic benefit cost: Service cost $ 2,191 $ 2,394 $ 6,001 $ 6,594 $ 8,199 $ 8,707 Interest cost 3,250 3,622 9,780 10,872 13,403 14,563 Expected return on plan assets (4,734 ) (4,951 ) (14,159 ) (14,846 ) (19,108 ) (19,528 ) Amortization of: Net loss 1,730 2,485 5,505 7,985 8,167 10,267 Prior service benefit (875 ) (855 ) (2,630 ) (2,630 ) (3,506 ) (3,506 ) Net periodic benefit cost $ 1,562 $ 2,695 $ 4,497 $ 7,975 $ 7,155 $ 10,503
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Schedule of Net Benefit Costs	The net periodic benefit cost recognized for the three, nine and twelve months ended September 30, 2016 and 2015 is made up of the components listed below (in thousands): Three Months Ended Nine Months Ended Twelve Months Ended September 30, September 30, September 30, 2016 2015 2016 2015 2016 2015 Components of net periodic benefit cost: Service cost $ 749 $ 841 $ 2,179 $ 2,591 $ 3,042 $ 3,302 Interest cost 871 976 2,616 3,026 3,625 4,142 Expected return on plan assets (452 ) (503 ) (1,372 ) (1,553 ) (1,889 ) (2,082 ) Amortization of: Prior service benefit (788 ) (751 ) (2,363 ) (2,301 ) (3,130 ) (3,490 ) Net gain (643 ) (519 ) (1,973 ) (1,519 ) (2,479 ) (2,186 ) Net periodic benefit cost (benefit) $ (263 ) $ 44 $ (913 ) $ 244 $ (831 ) $ (314 )

Financial Instruments And Inv25

Financial Instruments And Investments (Tables)	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Fair Values Of Long-Term Debt And Short-Term Borrowings Under the RCF	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): September 30, 2016 December 31, 2015 Carrying Amount (1) Estimated Fair Value Carrying Amount (1) Estimated Fair Value Pollution Control Bonds $ 190,706 $ 211,050 $ 190,499 $ 212,624 Senior Notes 993,004 1,207,162 837,475 829,864 RGRT Senior Notes (2) 94,768 100,465 94,686 100,345 RCF (2) 55,192 55,192 141,738 141,738 Total $ 1,333,670 $ 1,573,869 $ 1,264,398 $ 1,284,571 _______________ (1) The Company implemented ASU 2015-03, Interest - Imputation of Interest, which requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability. ASU 2015-03 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. The impact of ASU 2015-03 on the Company's Balance Sheet was to reclassify $11.6 million of other deferred charges to long-term debt, net of current portion at December 31, 2015. (2) Nuclear fuel financing, as of September 30, 2016 and December 31, 2015 , is funded through the $95 million RGRT Senior Notes and $36.2 million and $33.7 million , respectively under the RCF. As of September 30, 2016 , $19.0 million was outstanding under the RCF for working capital or general corporate purposes. As of December 31, 2015 , $108.0 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): September 30, 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 (1) : Federal Agency Mortgage Backed Securities $ 1,028 $ (9 ) $ — $ — $ 1,028 $ (9 ) U.S. Government Bonds 8,728 (151 ) 12,300 (526 ) 21,028 (677 ) Municipal Obligations 4,692 (43 ) 8,171 (515 ) 12,863 (558 ) Corporate Obligations 3,380 (50 ) 2,381 (138 ) 5,761 (188 ) Total Debt Securities 17,828 (253 ) 22,852 (1,179 ) 40,680 (1,432 ) Common Stock 1,393 (124 ) — — 1,393 (124 ) Institutional Equity Funds-International Equity 22,847 (249 ) — — 22,847 (249 ) Total Temporarily Impaired Securities $ 42,068 $ (626 ) $ 22,852 $ (1,179 ) $ 64,920 $ (1,805 ) _________________ (1) Includes 104 securities. December 31, 2015 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 $ 9,383 $ (97 ) $ 1,113 $ (47 ) $ 10,496 $ (144 ) U.S. Government Bonds 24,094 (310 ) 14,272 (623 ) 38,366 (933 ) Municipal Obligations 8,286 (160 ) 7,388 (446 ) 15,674 (606 ) Corporate Obligations 6,058 (722 ) 2,307 (228 ) 8,365 (950 ) Total Debt Securities 47,821 (1,289 ) 25,080 (1,344 ) 72,901 (2,633 ) Common Stock 3,584 (344 ) — — 3,584 (344 ) Institutional Equity Funds-International Equity 22,454 (768 ) — — 22,454 (768 ) Total Temporarily Impaired Securities $ 73,859 $ (2,401 ) $ 25,080 $ (1,344 ) $ 98,939 $ (3,745 ) _________________ (2) Includes 133 securities.
Unrealized Holding Losses Included In Pre-Tax Income	For the three, nine and twelve months ended September 30, 2016 and 2015 , the Company recognized other than temporary impairment losses on its available-for-sale securities as follow (in thousands): Three Months Ended Nine Months Ended Twelve Months Ended September 30, September 30, September 30, 2016 2015 2016 2015 2016 2015 Unrealized holding losses included in pre-tax income $ (196 ) $ — $ (352 ) $ — $ (690 ) $ —
Available-For-Sale-Securities, Continuous Unrealized Gain Position	The table below presents the unrecognized gross unrealized gains and the fair value of these securities, aggregated by investment category (in thousands): September 30, 2016 December 31, 2015 Fair Value Unrealized Gains Fair Value Unrealized Gains Description of Securities: Federal Agency Mortgage Backed Securities $ 16,772 $ 701 $ 9,589 $ 438 U.S. Government Bonds 35,711 1,285 12,033 136 Municipal Obligations 9,273 398 8,671 332 Corporate Obligations 18,368 1,347 10,110 368 Total Debt Securities 80,124 3,731 40,403 1,274 Common Stock 66,055 34,418 72,636 37,001 Equity Mutual Funds 35,552 1,995 18,853 91 Cash and Cash Equivalents 7,975 — 8,204 — Total $ 189,706 $ 40,144 $ 140,096 $ 38,366
Contractual Year For Maturity Of Available-For-Sale Securities	The contractual year for maturity of these available-for-sale securities as of September 30, 2016 is as follows (in thousands): Total 2016 2017 2021 through 2025 2026 and Beyond Municipal Debt Obligations $ 22,136 $ 417 $ 7,909 $ 12,730 $ 1,080 Corporate Debt Obligations 24,129 — 5,501 9,941 8,687 U.S. Government Bonds 56,739 — 29,297 14,542 12,900
Sale of Securities And The Related Effects On Pre-Tax Income	The proceeds from the sale of these securities during the three, nine, and twelve months ended September 30, 2016 and 2015 and the related effects on pre-tax income are as follows (in thousands): Three Months Ended Nine Months Ended Twelve Months Ended September 30, September 30, September 30, 2016 2015 2016 2015 2016 2015 Proceeds from sales or maturities of available-for-sale securities $ 19,453 $ 26,618 $ 60,165 $ 63,776 $ 98,956 $ 124,732 Gross realized gains included in pre-tax income $ 2,446 $ 4,515 $ 6,687 $ 8,330 $ 10,736 $ 12,467 Gross realized losses included in pre-tax income (178 ) (191 ) (765 ) (443 ) (1,249 ) (1,021 ) Gross unrealized losses included in pre-tax income (196 ) — (352 ) — (690 ) — Net gains included in pre-tax income $ 2,072 $ 4,324 $ 5,570 $ 7,887 $ 8,797 $ 11,446 Net unrealized holding gains (losses) included in accumulated other comprehensive income $ 4,313 $ (8,092 ) $ 9,293 $ (8,641 ) $ 15,028 $ (5,779 ) Net gains reclassified from accumulated other comprehensive income (2,072 ) (4,324 ) (5,570 ) (7,887 ) (8,797 ) (11,446 ) Net gains (losses) in other comprehensive income $ 2,241 $ (12,416 ) $ 3,723 $ (16,528 ) $ 6,231 $ (17,225 )
Fair Value, Measurement Inputs, Disclosure	The fair value of the Company's decommissioning trust funds and investments in debt securities at September 30, 2016 and December 31, 2015 , 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 September 30, 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 $ 1,398 $ — $ — $ 1,398 Available for sale: U.S. Government Bonds $ 56,739 $ 56,739 $ — $ — Federal Agency Mortgage Backed Securities 17,800 — 17,800 — Municipal Bonds 22,136 — 22,136 — Corporate Asset Backed Obligations 24,129 — 24,129 — Subtotal Debt Securities 120,804 56,739 64,065 — Common Stock 67,448 67,448 — — Equity Mutual Funds 35,552 35,552 — — Institutional Funds-International Equity 22,847 22,847 — — Cash and Cash Equivalents 7,975 7,975 — — Total Available for Sale $ 254,626 $ 190,561 $ 64,065 $ — Description of Securities Fair Value as of December 31, 2015 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 $ 1,543 $ — $ — $ 1,543 Available for sale: U.S. Government Bonds $ 50,399 $ 50,399 $ — $ — Federal Agency Mortgage Backed Securities 20,085 — 20,085 — Municipal Bonds 24,345 — 24,345 — Corporate Asset Backed Obligations 18,475 — 18,475 — Subtotal Debt Securities 113,304 50,399 62,905 — Common Stock 76,220 76,220 — — Equity Mutual Funds 18,853 18,853 — — Institutional Funds-International Equity 22,454 22,454 — — Cash and Cash Equivalents 8,204 8,204 — — Total Available for Sale $ 239,035 $ 176,130 $ 62,905 $ —

Principles Of Preparation (Accr

Principles Of Preparation (Accrued Unbilled Revenues) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Accrued unbilled revenues	$ 30.3	$ 21.7

Principles Of Preparation (Supp

Principles Of Preparation (Supplemental Cash Flow Disclosures) (Details) - USD ($) $ in Thousands		Jul. 06, 2016	Sep. 30, 2016	Sep. 30, 2015
Supplemental Cash Flow Information [Abstract]
Interest on long-term debt and borrowing under the revolving credit facility			$ 46,867	$ 41,406
Income tax paid (refunded), net			3,337	(272)
Sale of Interest in Four Corners Generating Station	[1]		27,720	0
Changes in accrued plant additions			4,277	(13,150)
Site Contingency [Line Items]
Proceeds from Sale of Property, Plant, and Equipment			3,251	644
Four Corners Generating Station
Site Contingency [Line Items]
Property, Plant and Equipment, Disposals		$ 32,000
Asset Retirement Obligation		7,000
Mine Reclamation Liability, Noncurrent		19,500
Public Utilities, Property, Plant and Equipment, Amount of Disposal Adjustments		1,300
Proceeds from Sale of Property, Plant, and Equipment		4,200
Accounts Payable		$ 1,600
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants of restricted shares of common stock			$ 1,236	$ 1,106
[1]	The Company sold its interest in the Four Corners Generating Station ("Four Corners") for approximately $32.0 million based on the book value as defined in the asset purchase agreement entered into by the Company and Arizona Public Service Company ("APS") on February 17, 2015 (the "Purchase and Sale Agreement"). The sales price was adjusted downward by $7.0 million and $19.5 million, respectively, to reflect APS assumption of the Company's obligation to pay for future plant decommissioning and mine reclamation expense. The sales price was also adjusted downward by approximately $1.3 million for closing adjustments and other assets and liabilities assumed by APS. At the closing of the sale, the Company received approximately $4.2 million in cash, subject to post-closing adjustments. Subsequently, the Company recorded post-closing adjustments to reflect adjustments to estimated capital expenditures and other assets and liabilities assumed by APS through July 6, 2016, which resulted in a $1.6 million refund due to APS.

Principles Of Preparation (Depr

Principles Of Preparation (Depreciation) (Details) - Public Utilities, Regulatory Rate Making Impact - PUCT - USD ($) $ in Thousands	Aug. 25, 2016	Sep. 30, 2016	Sep. 30, 2016
Property, Plant and Equipment [Line Items]
Decrease in Depreciation Expense	$ 8,500	$ 7,400	$ 7,400
Expected Decrease In Depreciation Expense			$ 9,500

Accumulated Other Comprehensi29

Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance				$ (13,914)
Accumulated Other Comprehensive Income (Loss), ending balance		$ (12,337)		(12,337)		$ (12,337)
Accumulated Defined Benefit Plans Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance		(30,532)	$ (34,331)	(29,869)	$ (34,884)	(34,105)	$ (9,818)
Other Comprehensive Income (Loss) before Reclassifications		0	0	0	0	3,777	(24,775)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	[1]	(804)	226	(1,467)	779	(1,008)	488
Accumulated Other Comprehensive Income (Loss), ending balance		(31,336)	(34,105)	(31,336)	(34,105)	(31,336)	(34,105)
Accumulated Net Unrealized Investment Gain (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance		28,925	35,726	27,765	38,957	25,769	39,525
Other Comprehensive Income (Loss) before Reclassifications		3,493	(6,485)	7,459	(6,854)	12,058	(4,537)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)		(1,687)	(3,472)	(4,493)	(6,334)	(7,096)	(9,219)
Accumulated Other Comprehensive Income (Loss), ending balance		30,731	25,769	30,731	25,769	30,731	25,769
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		(11,693)	(11,959)	(11,810)	(12,074)	(11,887)	(12,146)
Other Comprehensive Income (Loss) before Reclassifications		0	0	0	0	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)		(39)	72	78	187	155	259
Accumulated Other Comprehensive Income (Loss), ending balance		(11,732)	(11,887)	(11,732)	(11,887)	(11,732)	(11,887)
Accumulated Other Comprehensive Income (Loss), Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance		(13,300)	(10,564)	(13,914)	(8,001)	(20,223)	17,561
Other Comprehensive Income (Loss) before Reclassifications		3,493	(6,485)	7,459	(6,854)	15,835	(29,312)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)		(2,530)	(3,174)	(5,882)	(5,368)	(7,949)	(8,472)
Accumulated Other Comprehensive Income (Loss), ending balance		$ (12,337)	$ (20,223)	$ (12,337)	$ (20,223)	$ (12,337)	$ (20,223)
[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		9 Months Ended		12 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income (Loss) before income tax		$ 117,770	$ 81,340	$ 142,535	$ 116,359	$ 142,989	$ 122,790
Income tax expense		(43,134)	(24,600)	(51,423)	(35,089)	(51,229)	(37,279)
Net (Income) Loss		74,636	56,740	91,112	81,270	91,760	85,511
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]	1,663	1,606	4,993	4,931	6,636	6,996
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]	(1,087)	(1,966)	(3,532)	(6,466)	(5,688)	(8,081)
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]	576	(360)	1,461	(1,535)	948	(1,085)
Reclassification from AOCI, Current Period, Tax		228	134	6	756	60	597
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	804	(226)	1,467	(779)	1,008	(488)
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		1,687	3,472	4,493	6,334	7,096	9,219
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		39	(72)	(78)	(187)	(155)	(259)
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		2,530	3,174	5,882	5,368	7,949	8,472
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		2,072	4,324	5,570	7,887	8,797	11,446
Income (Loss) before income tax		2,072	4,324	5,570	7,887	8,797	11,446
Income tax expense		(385)	(852)	(1,077)	(1,553)	(1,701)	(2,227)
Net (Income) Loss		1,687	3,472	4,493	6,334	7,096	9,219
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 tax		(126)	(118)	(371)	(348)	(490)	(460)
Income tax expense		165	46	293	161	335	201
Net (Income) Loss		39	(72)	(78)	(187)	(155)	(259)
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		$ (126)	$ (118)	$ (371)	$ (348)	$ (490)	$ (460)
[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

Oct. 28, 2016USD ($)

Sep. 27, 2016USD ($)

Aug. 25, 2016USD ($)

Jul. 06, 2016USD ($)

Jun. 08, 2016USD ($)

Apr. 29, 2016USD ($)

Mar. 24, 2016USD ($)

Nov. 05, 2015USD ($)

Oct. 28, 2015USD ($)

Aug. 10, 2015USD ($)

May 20, 2015

May 11, 2015USD ($)

May 01, 2015USD ($)

Feb. 17, 2015

Dec. 01, 2014USD ($)

Sep. 30, 2016USD ($)

Mar. 31, 2016USD ($)

Sep. 30, 2015USD ($)

Sep. 30, 2016USD ($)MW

Sep. 30, 2015USD ($)

Sep. 30, 2016USD ($)

Sep. 30, 2015USD ($)

Dec. 31, 2015USD ($)

Oct. 19, 2015USD ($)

Oct. 07, 2015USD ($)

Operating revenues

$ 323,225

$ 289,713

$ 698,899

$ 672,967

$ 875,801

$ 869,530

Income before income taxes

117,770

81,340

142,535

116,359

142,989

122,790

Net income

74,636

$ 56,740

91,112

81,270

91,760

$ 85,511

Deferred Fuel Cost

8,962

8,962

8,962

$ 0

Over-collection of fuel revenues

1,219

1,219

1,219

4,023

Jointly Owned Utility Plant, Proportionate Ownership Share

7.00%

Proceeds from issuance of senior notes

157,052

$ 0

Interest Payable, Current

$ 19,349

$ 19,349

$ 19,349

$ 12,649

Four Corners Generating Station

Purchase and Sale Agreement, Execution Date

Feb. 17, 2015

Closing Date of Sale

Jul. 6, 2016

Mine Reclamation Liability, Noncurrent

$ 19,500

PUCT

Public Utilities Requested Performance Incentive Bonus Related To Energy Efficiency Program

$ 668

$ 1,000

Public Utilities Approved Performance Incentive Bonus Related To Energy Efficiency Program

$ 1,000

Fuel Over And Under Materiality Threshold Percentage

4.00%

4.00%

4.00%

Deferred Fuel Cost

$ 8,900

$ 8,900

$ 8,900

PUCT | Four Corners Generating Station

Purchase and Sale Agreement, Execution Date

Feb. 17, 2015

PUCT | Montana Power Station Units 1 and 2

Property, Plant and Equipment, Operational Date

Mar. 20, 2015

PUCT | Montana Power Station Unit 3

Property, Plant and Equipment, Operational Date

May 3, 2016

PUCT | Montana Power Station Unit 4

Property, Plant and Equipment, Operational Date

Sep. 15, 2016

PUCT | Community Solar At Montana Power Station

Electric Capacity | MW

3

PUCT | Minimum

Fixed Fuel Factor Revision Period, in Months

4 months

PUCT | Four Corners Generating Station

Closing Date of Sale

Jul. 6, 2016

Mine Reclamation Liability, Noncurrent

7,500

$ 7,500

7,500

PUCT | Subsequent Event

Public Utilities Approved Performance Incentive Bonus Related To Energy Efficiency Program

$ 500

Public Utilities Requested Performance Incentive Bonus Related To Energy Efficiency Program Reduction, Amount

$ 155

NMPRC

Over-collection of fuel revenues

$ 1,300

$ 1,300

$ 1,300

Debt Instrument, Face Amount

$ 310,000

NMPRC | Four Corners Generating Station

Purchase and Sale Agreement, Execution Date

Feb. 17, 2015

NMPRC | Montana Power Station Units 1 and 2

Property, Plant and Equipment, Operational Date

Mar. 20, 2015

NMPRC | Montana Power Station Unit 3

Property, Plant and Equipment, Operational Date

May 3, 2016

NMPRC | Montana Power Station Unit 4

Property, Plant and Equipment, Operational Date

Sep. 15, 2016

NMPRC | Holloman

Electric Capacity | MW

5

NMPRC | Four Corners Generating Station

Jointly Owned Utility Plant, Proportionate Ownership Share

7.00%

7.00%

7.00%

FERC

Debt Instrument, Face Amount

$ 310,000

Line of Credit Facility, Maximum Borrowing Capacity

400,000

Debt Issuance Authorization Date Range Start

Nov. 15, 2015

Debt Issuance Authorization Date Range End

Nov. 15, 2017

FERC | Four Corners Generating Station

Closing Date of Sale

Jul. 6, 2016

Jointly Owned Utility Plant Entire Ownership Of Proportionate Interest, Percentage

100.00%

100.00%

100.00%

RGRT | NMPRC

Debt Instrument, Face Amount

$ 65,000

RGRT | FERC

Debt Instrument, Face Amount

$ 65,000

5.00% Senior Notes, Plus Premium, Due 2044 | NMPRC

Debt Instrument, Face Amount

$ 150,000

Debt Instrument, Issuance Date

Mar. 24, 2016

Debt Instrument, Interest Rate, Stated Percentage

5.00%

Debt Instrument, Maturity Date

Dec. 1, 2044

Proceeds from issuance of senior notes

$ 158,100

Interest Payable, Current

2,400

Debt Instrument, Unamortized Premium

7,100

5.00% Senior Notes, Plus Premium, Due 2044 | FERC

Debt Instrument, Face Amount

$ 150,000

Debt Instrument, Issuance Date

Mar. 24, 2016

Debt Instrument, Interest Rate, Stated Percentage

5.00%

Debt Instrument, Maturity Date

Dec. 1, 2044

Proceeds from issuance of senior notes

$ 158,100

Interest Payable, Current

2,400

Debt Instrument, Unamortized Premium

$ 7,100

5.00% Senior Notes, Net of Discount, Due 2044 | NMPRC

Debt Instrument, Face Amount

$ 150,000

Debt Instrument, Issuance Date

Dec. 1, 2014

Debt Instrument, Interest Rate, Stated Percentage

5.00%

Debt Instrument, Maturity Date

Dec. 1, 2044

5.00% Senior Notes, Net of Discount, Due 2044 | FERC

Debt Instrument, Face Amount

$ 150,000

Debt Instrument, Issuance Date

Dec. 1, 2014

Debt Instrument, Interest Rate, Stated Percentage

5.00%

Debt Instrument, Maturity Date

Dec. 1, 2044

5.00% Senior Notes, Combined, Due 2044 | NMPRC

Debt Instrument, Face Amount

$ 300,000

$ 300,000

$ 300,000

5.00% Senior Notes, Combined, Due 2044 | FERC

Debt Instrument, Face Amount

300,000

$ 300,000

$ 300,000

Electric Generation Equipment | PUCT | Montana Power Station

Number of power generation units authorized to be constructed

4

Electric Generation Equipment | NMPRC | Montana Power Station

Number of power generation units authorized to be constructed

4

Non-Fuel Base Rate | PUCT

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 71,500

Public Utilities, Requested Rate Increase, Amended, Amount

$ 63,300

Non-Fuel Base Rate | NMPRC

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 8,600

Public Utilities, Requested Rate Increase, Amended, Amount

$ 6,400

Public Utilities, Approved Rate Increase, Amount

$ 1,100

Public Utilities, Approved Return on Equity, Percentage

9.48%

Public Utilities, Requested Rate Increase (Decrease), Percentage

7.10%

Public Utilities, Regulatory Rate Making Impact | PUCT

Public Utilities, Depreciation Expense Decrease

$ 8,500

7,400

$ 7,400

Public Utilities, Approved Return on Equity, Percentage

9.70%

Recovery of rate case expenses

$ 3,100

Period To Relate Back New Rates

80 days

Operating revenues

34,800

Increase in other expenses

1,900

Income before income taxes

40,300

Net income

$ 23,300

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

Public Utilities, Approved Rate Increase, Amount

$ 37,000

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. 12, 2017

Public Utilities, Regulatory Rate Making Impact | Relate Back Of Rates Revenue | PUCT

Operating revenues

$ 4,800

PUCT Docket No. 44633 | Fixed Fuel Factor

Decrease In Fixed Fuel Factor, Percentage

24.00%

PUCT Docket No. 46308

Reconcilable Fuel Expense

$ 436,600

Fuel Reconciliation Period

36 months

Palo Verde and Four Corners (N

Palo Verde and Four Corners (Narrative) (Details) - USD ($) $ in Thousands

Oct. 31, 2016

Jul. 06, 2016

Mar. 31, 2016

Nov. 02, 2015

Jun. 01, 2015

Feb. 17, 2015

Oct. 31, 2014

Oct. 08, 2014

Aug. 18, 2014

Dec. 19, 2012

Sep. 30, 2016

Sep. 30, 2015

Jointly Owned Utility Plant Interests [Line Items]

Proceeds from Sale of Property, Plant, and Equipment

$ 3,251

$ 644

Refund passed through to customers

$ (11,766)

$ 10,934

Four Corners Generating Station

Jointly Owned Utility Plant Interests [Line Items]

Mine Reclamation Liability, Noncurrent

$ 19,500

Public Utilities, Property, Plant and Equipment, Amount of Disposal Adjustments

$ 1,300

Disposal Date

Jul. 6, 2016

Property, Plant and Equipment, Disposals

$ 32,000

Asset Retirement Obligation

7,000

Proceeds from Sale of Property, Plant, and Equipment

4,200

Purchase and Sale Agreement, Execution Date

Feb. 17, 2015

Accounts Payable

$ 1,600

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

November 2, 2015

October 31, 2014

December 19, 2012

Settlement Agreement, Date

August 18, 2014

Suit Against Department of Energy for Spent Fuel | Palo Verde Generating Station

Jointly Owned Utility Plant Interests [Line Items]

Settlement, Amount

$ 1,900

$ 6,600

$ 9,100

Refund passed through to customers

$ 1,600

$ 5,800

$ 7,900

Settlement Agreement Award Received, Date

Mar. 31, 2016

Jun. 1, 2015

Oct. 8, 2014

Suit Against Department of Energy for Spent Fuel | Palo Verde Participants

Jointly Owned Utility Plant Interests [Line Items]

Settlement, Amount

$ 12,000

$ 42,000

$ 57,400

Minimum | Suit Against Department of Energy for Spent Fuel

Jointly Owned Utility Plant Interests [Line Items]

Litigation, Period Covered

July 1, 2014

July 1, 2011

January 1, 2007

Maximum | Suit Against Department of Energy for Spent Fuel

Jointly Owned Utility Plant Interests [Line Items]

Litigation, Period Covered

June 30, 2015

June 30, 2014

June 30, 2011

Subsequent Event | Suit Against Department of Energy for Spent Fuel

Jointly Owned Utility Plant Interests [Line Items]

Lawsuit Filing Date

October 31, 2016

Subsequent Event | Suit Against Department of Energy for Spent Fuel | Palo Verde Generating Station

Jointly Owned Utility Plant Interests [Line Items]

Litigation, Claim Amount

$ 1,800

Subsequent Event | Suit Against Department of Energy for Spent Fuel | Palo Verde Participants

Jointly Owned Utility Plant Interests [Line Items]

Litigation, Claim Amount

$ 11,300

Subsequent Event | Minimum | Suit Against Department of Energy for Spent Fuel

Jointly Owned Utility Plant Interests [Line Items]

Litigation, Period Covered

July 1, 2015

Subsequent Event | Maximum | Suit Against Department of Energy for Spent Fuel

Jointly Owned Utility Plant Interests [Line Items]

Litigation, Period Covered

June 30, 2016

Palo Verde Operations and Maint

Palo Verde Operations and Maintenance Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Palo Verde Generating Station
Operations & Maintenance Expenses [Line Items]
Utilities Operating Expense, Maintenance and Operations	$ 21,123	$ 22,016	$ 67,514	$ 67,702	$ 97,451	$ 98,884

Common Stock (Narrative) (Detai

Common Stock (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Dividends, Common Stock [Abstract]
Dividends, Common Stock, Cash	$ 12,500	$ 11,900	$ 37,021	$ 35,138	$ 49,000	$ 46,400

Common Stock (Basic And Diluted

Common Stock (Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Basic number of common shares outstanding	40,363,819	40,289,010	40,344,834	40,267,533	40,332,835	40,255,439
Dilutive effect of unvested performance awards	62,123	40,519	50,977	32,268	47,608	24,201
Diluted number of common shares outstanding	40,425,942	40,329,529	40,395,811	40,299,801	40,380,443	40,279,640
Net income	$ 74,636	$ 56,740	$ 91,112	$ 81,270	$ 91,760	$ 85,511
Income allocated to participating restricted stock	(232)	(184)	(271)	(253)	(264)	(265)
Net income available to common shareholders, basic	74,404	56,556	90,841	81,017	91,496	85,246
Income reallocated to participating restricted stock	(232)	(184)	(271)	(253)	(264)	(265)
Net income available to common shareholders, diluted	$ 74,404	$ 56,556	$ 90,841	$ 81,017	$ 91,496	$ 85,246
Earnings Per Share, Basic, Distributed	$ 0.310	$ 0.295	$ 0.915	$ 0.870	$ 1.21	$ 1.15
Earnings Per Share, Basic, Undistributed	1.530	1.105	1.335	1.140	1.06	0.97
Basic net income per common share	1.840	1.400	2.250	2.010	2.270	2.120
Earnings Per Share, Diluted, Distributed	0.310	0.295	0.915	0.870	1.21	1.15
Earnings Per Share, Diluted, Undistributed	1.530	1.105	1.335	1.140	1.06	0.97
Diluted net income per common share	$ 1.840	$ 1.400	$ 2.250	$ 2.010	$ 2.270	$ 2.120

Common Stock (Antidilutive Secu

Common Stock (Antidilutive Securities Excluded From Computation Of Earnings Per Share) (Details) - shares		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
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		57,633	65,076	53,285	60,647	50,854	60,742
Performance Shares
Antidilutive Securities Excluded from the Computation of Diluted Earnings Per Share, Amount	[1]	62,995	59,898	62,995	59,898	62,995	63,111
[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		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Tax [Line Items]
Consolidated effective tax rate	36.60%	30.20%	36.10%	30.20%	35.80%	30.40%
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	Jun. 30, 2016	Sep. 30, 2016	Mar. 31, 2016	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Tax [Line Items]
Deferred Income Tax Expense (Benefit)					$ 48,457	$ 32,090
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions					1,200	$ 100
Accounting Standards Update 2015-17
Income Tax [Line Items]
Amounts previously reported, reclassified					$ 21,600
Internal Revenue Service (IRS) | Maximum
Income Tax [Line Items]
Tax Year Closed					2,011
NEW MEXICO | Maximum
Income Tax [Line Items]
Tax Year Closed					2,011
TEXAS
Income Tax [Line Items]
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions		$ 900		$ 100
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					2,011
ARIZONA
Income Tax [Line Items]
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities			$ 300
ARIZONA | Earliest Tax Year
Income Tax [Line Items]
Tax Year Closed	2,009
ARIZONA | Latest Tax Year
Income Tax [Line Items]
Tax Year Closed	2,012
Change in Accounting Method Accounted for as Change in Estimate
Income Tax [Line Items]
Deferred Income Tax Expense (Benefit)		$ 2,800

Income Taxes (Unrecognized Tax

Income Taxes (Unrecognized Tax Benefits) [Roll Forward] (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at the beginning of period	$ 6,000	$ 5,200
Additions for tax position related to the current year	0	0
Reductions for tax positions related to the current year	0	0
Additions for tax positions of prior years	0	0
Reductions for tax positions	1,200	100
Balance at the end of period	$ 4,800	$ 5,100

Commitments, Contingencies An40

Commitments, Contingencies And Uncertainties (Narrative) (Details)	Jul. 06, 2016	Apr. 22, 2016Countries	Sep. 30, 2016Decimals	Jul. 28, 2015States
Loss Contingencies [Line Items]
Number of States Affected by EPA's Emissions Budgets | States				13
Number of criteria emissions established under the Clear Air Act			6
Frequency of Review by Environmental Protection Agency			5 years
Jointly Owned Utility Plant, Proportionate Ownership Share	7.00%
Number of countries that signed the Paris Agreement | Countries		175
Frequency of Review by Countries Participating in the Paris Agreement		5 years
Four Corners Generating Station
Loss Contingencies [Line Items]
Date participation is ceased	Jul. 6, 2016
Minimum
Loss Contingencies [Line Items]
Public Utilities, Government Standard Emission Limit			70
Maximum
Loss Contingencies [Line Items]
Public Utilities, Government Standard Emission Limit			75

Employee Benefits (Retirement P

Employee Benefits (Retirement Plans And Other Postretirement Benefits) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,191	$ 2,394	$ 6,001	$ 6,594	$ 8,199	$ 8,707
Interest cost	3,250	3,622	9,780	10,872	13,403	14,563
Expected return on plan assets	(4,734)	(4,951)	(14,159)	(14,846)	(19,108)	(19,528)
Amortization of prior service benefit	(875)	(855)	(2,630)	(2,630)	(3,506)	(3,506)
Amortization of net (gain) loss	1,730	2,485	5,505	7,985	8,167	10,267
Net periodic benefit cost (benefit)	1,562	2,695	4,497	7,975	7,155	10,503
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	749	841	2,179	2,591	3,042	3,302
Interest cost	871	976	2,616	3,026	3,625	4,142
Expected return on plan assets	(452)	(503)	(1,372)	(1,553)	(1,889)	(2,082)
Amortization of prior service benefit	(788)	(751)	(2,363)	(2,301)	(3,130)	(3,490)
Amortization of net (gain) loss	(643)	(519)	(1,973)	(1,519)	(2,479)	(2,186)
Net periodic benefit cost (benefit)	$ (263)	$ 44	$ (913)	$ 244	$ (831)	$ (314)

Employee Benefits (Narrative) (

Employee Benefits (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2016USD ($)	Jan. 01, 2017	Oct. 01, 2016USD ($)
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Employer Contribution	$ 8.8
Defined Benefit Plan, Expected Contributions in Current Fiscal Year	9.4
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Employer Contribution	1.6
Defined Benefit Plan, Expected Contributions in Current Fiscal Year	$ 1.7
Subsequent Event | Other Postretirement Benefit Plans
Defined Benefit Plan, Plan Amendment [Abstract]
Defined Benefit Plan, decrease in benefit obligation			$ 32.7
$1,000 or $2,250 deductible plan options | Scenario, Forecast | Maximum | Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Age Eligible for Benefit		65
Medicare advantage plan | Scenario, Forecast | Minimum | Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Age Eligible for Benefit		65

Financial Instruments And Inv43

Financial Instruments And Investments (Carrying Amount and Fair Value Amounts) (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
Carrying (Reported) Amount, Fair Value Disclosure
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[1]	$ 1,333,670	$ 1,264,398
Carrying (Reported) Amount, Fair Value Disclosure | Pollution Control Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[1]	190,706	190,499
Carrying (Reported) Amount, Fair Value Disclosure | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[1]	993,004	837,475
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],[2]	94,768	94,686
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],[2]	55,192	141,738
Estimate of Fair Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		1,573,869	1,284,571
Estimate of Fair Value Measurement | Pollution Control Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		211,050	212,624
Estimate of Fair Value Measurement | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		1,207,162	829,864
Estimate of Fair Value Measurement | RGRT Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[2]	100,465	100,345
Estimate of Fair Value Measurement | Revolving Credit Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[2]	$ 55,192	$ 141,738
[1]	The Company implemented ASU 2015-03, Interest - Imputation of Interest, which requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability. ASU 2015-03 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. The impact of ASU 2015-03 on the Company's Balance Sheet was to reclassify $11.6 million of other deferred charges to long-term debt, net of current portion at December 31, 2015.
[2]	Nuclear fuel financing, as of September 30, 2016 and December 31, 2015, is funded through the $95 million RGRT Senior Notes and $36.2 million and $33.7 million, respectively under the RCF. As of September 30, 2016, $19.0 million was outstanding under the RCF for working capital or general corporate purposes. As of December 31, 2015, $108.0 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 Inv44

Financial Instruments And Investments (Long-Term Debt and Short-Term Borrowings - Narratives) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Financial Instruments and Investments [Line Items]
Decommissioning Fund Investments	$ 254,626	$ 239,035
Accounting Standards Update 2015-03
Financial Instruments and Investments [Line Items]
Amounts previously reported, reclassified	11,600
Nuclear Fuel Financing
Financial Instruments and Investments [Line Items]
Line of Credit Facility, Amount Outstanding	36,200	33,700
Working Capital and General Purpose
Financial Instruments and Investments [Line Items]
Line of Credit Facility, Amount Outstanding	19,000	108,000
RGRT Senior Notes
Financial Instruments and Investments [Line Items]
Long-term Debt, Gross	$ 95,000	$ 95,000

Financial Instruments And Inv45

Financial Instruments And Investments (Marketable Securities Fair Value And Unrealized Losses) (Details) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2016USD ($)securities		Dec. 31, 2015USD ($)securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months	$ 42,068	[1]	$ 73,859	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(626)	[1]	(2,401)	[2]
Marketable Securities Fair Value 12 Months or Longer	22,852	[1]	25,080	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(1,179)	[1]	(1,344)	[2]
Marketable Securities Fair Value Total	64,920	[1]	98,939	[2]
Marketable Securities Unrealized Losses Total	$ (1,805)	[1]	$ (3,745)	[2]
Number of securities | securities	104		133
Debt Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months	$ 17,828	[1]	$ 47,821	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(253)	[1]	(1,289)	[2]
Marketable Securities Fair Value 12 Months or Longer	22,852	[1]	25,080	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(1,179)	[1]	(1,344)	[2]
Marketable Securities Fair Value Total	40,680	[1]	72,901	[2]
Marketable Securities Unrealized Losses Total	(1,432)	[1]	(2,633)	[2]
Collateralized Mortgage Backed Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months	1,028	[1]	9,383	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(9)	[1]	(97)	[2]
Marketable Securities Fair Value 12 Months or Longer	0	[1]	1,113	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	0	[1]	(47)	[2]
Marketable Securities Fair Value Total	1,028	[1]	10,496	[2]
Marketable Securities Unrealized Losses Total	(9)	[1]	(144)	[2]
U.S. Government Bonds
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months	8,728	[1]	24,094	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(151)	[1]	(310)	[2]
Marketable Securities Fair Value 12 Months or Longer	12,300	[1]	14,272	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(526)	[1]	(623)	[2]
Marketable Securities Fair Value Total	21,028	[1]	38,366	[2]
Marketable Securities Unrealized Losses Total	(677)	[1]	(933)	[2]
Municipal Bonds
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months	4,692	[1]	8,286	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(43)	[1]	(160)	[2]
Marketable Securities Fair Value 12 Months or Longer	8,171	[1]	7,388	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(515)	[1]	(446)	[2]
Marketable Securities Fair Value Total	12,863	[1]	15,674	[2]
Marketable Securities Unrealized Losses Total	(558)	[1]	(606)	[2]
Corporate Debt Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months	3,380	[1]	6,058	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(50)	[1]	(722)	[2]
Marketable Securities Fair Value 12 Months or Longer	2,381	[1]	2,307	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(138)	[1]	(228)	[2]
Marketable Securities Fair Value Total	5,761	[1]	8,365	[2]
Marketable Securities Unrealized Losses Total	(188)	[1]	(950)	[2]
Equity Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months	1,393	[1]	3,584	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(124)	[1]	(344)	[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	1,393	[1]	3,584	[2]
Marketable Securities Unrealized Losses Total	(124)	[1]	(344)	[2]
Institutional Funds-International Equity
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months	22,847	[1]	22,454	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(249)	[1]	(768)	[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	22,847	[1]	22,454	[2]
Marketable Securities Unrealized Losses Total	$ (249)	[1]	$ (768)	[2]
[1]	Includes 104 securities.
[2]	Includes 133 securities.

Financial Instruments And Inv46

Financial Instruments And Investments (Unrealized Holding Losses Included In Pre-Tax Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Financial Instruments And Investments [Abstract]
Unrealized losses included in pre-tax income	$ (196)	$ 0	$ (352)	$ 0	$ (690)	$ 0

Financial Instruments And Inv47

Financial Instruments And Investments (Unrecognized Gross Unrealized Gains And The Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	$ 189,706	$ 140,096
Cash and Cash Equivalents, at Carrying Value	10,044	8,149	$ 12,573	$ 40,504
Available-for-sale Securities, Gross Unrealized Gain	40,144	38,366
Debt Securities
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	80,124	40,403
Available-for-sale Securities, Gross Unrealized Gain	3,731	1,274
Collateralized Mortgage Backed Securities
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	16,772	9,589
Available-for-sale Securities, Gross Unrealized Gain	701	438
U.S. Government Bonds
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	35,711	12,033
Available-for-sale Securities, Gross Unrealized Gain	1,285	136
Municipal Bonds
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	9,273	8,671
Available-for-sale Securities, Gross Unrealized Gain	398	332
Corporate Debt Securities
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	18,368	10,110
Available-for-sale Securities, Gross Unrealized Gain	1,347	368
Equity Securities
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	66,055	72,636
Available-for-sale Securities, Gross Unrealized Gain	34,418	37,001
Mutual Funds - Equity
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	35,552	18,853
Available-for-sale Securities, Gross Unrealized Gain	1,995	91
Cash and Cash Equivalents
Financial Instruments and Investments [Line Items]
Cash and Cash Equivalents, at Carrying Value	7,975	8,204
Available-for-sale Securities, Gross Unrealized Gain	$ 0	$ 0

Financial Instruments And Inv48

Financial Instruments And Investments (Contractual Year For Maturity Of Available-For-Sale Securities ) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2016USD ($)
Collateralized Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Contractual Maturity Due For, Mortgaged Backed Securities	10 years
Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Total	$ 22,136
2,016	417
2017 through 2020	7,909
2021 through 2025	12,730
2026 and Beyond	1,080
Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Total	24,129
2,016	0
2017 through 2020	5,501
2021 through 2025	9,941
2026 and Beyond	8,687
U.S. Government Bonds
Schedule of Available-for-sale Securities [Line Items]
Total	56,739
2,016	0
2017 through 2020	29,297
2021 through 2025	14,542
2026 and Beyond	$ 12,900
Minimum | Collateralized Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Debt Instrument, Expected Weighted Average Maturity Year	2 years
Maximum | Collateralized Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Debt Instrument, Expected Weighted Average Maturity Year	6 years

Financial Instruments And Inv49

Financial Instruments And Investments (Sale Of Securities And The Related Effects On Pre-Tax Income ) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Investment [Line Items]
Proceeds from sales of available-for-sale securities	$ 19,453	$ 26,618	$ 60,165	$ 63,776	$ 98,956	$ 124,732
Gross realized gains included in pre-tax income	2,446	4,515	6,687	8,330	10,736	12,467
Gross realized losses included in pre-tax income	(178)	(191)	(765)	(443)	(1,249)	(1,021)
Gross unrealized losses included in pre-tax income	(196)	0	(352)	0	(690)	0
Net gains (losses) in pre-tax income	2,072	4,324	5,570	7,887	8,797	11,446
Net unrealized holding gains (losses) included in accumulated other comprehensive income	4,313	(8,092)	9,293	(8,641)	15,028	(5,779)
Net (gains) losses reclassified out of accumulated other comprehensive income	(2,072)	(4,324)	(5,570)	(7,887)	(8,797)	(11,446)
Net gains (losses) in other comprehensive income	$ 2,241	$ (12,416)	$ 3,723	$ (16,528)	$ 6,231	$ (17,225)

Financial Instruments And Inv50

Financial Instruments And Investments (Company's Decommissioning Trust Funds And Investments In Debt Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Financial Instruments and Investments [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 10,044	$ 8,149	$ 12,573	$ 40,504
Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	254,626	239,035
Decommisioning Fund Investments | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	190,561	176,130
Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	64,065	62,905
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	1,398	1,543
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	1,398	1,543
Debt Securities | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	120,804	113,304
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	56,739	50,399
Debt Securities | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	64,065	62,905
Debt Securities | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
U.S. Government Bonds | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	56,739	50,399
U.S. Government Bonds | Decommisioning Fund Investments | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	56,739	50,399
U.S. Government Bonds | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
U.S. Government Bonds | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Collateralized Mortgage Backed Securities | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	17,800	20,085
Collateralized 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
Collateralized Mortgage Backed Securities | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	17,800	20,085
Collateralized Mortgage Backed Securities | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Municipal Bonds | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	22,136	24,345
Municipal Bonds | 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 Bonds | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	22,136	24,345
Municipal Bonds | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Corporate Debt Securities | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	24,129	18,475
Corporate 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	0	0
Corporate Debt Securities | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	24,129	18,475
Corporate Debt Securities | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Equity Securities | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	67,448	76,220
Equity Securities | Decommisioning Fund Investments | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	67,448	76,220
Equity Securities | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	0	0
Equity Securities | 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	35,552	18,853
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	35,552	18,853
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	22,847	22,454
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	22,847	22,454
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 and Cash Equivalents
Financial Instruments and Investments [Line Items]
Cash and Cash Equivalents, at Carrying Value	7,975	8,204
Cash and Cash Equivalents | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Cash and Cash Equivalents, at Carrying Value	7,975	8,204
Cash and Cash Equivalents | Decommisioning Fund Investments | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Cash and Cash Equivalents, at Carrying Value	7,975	8,204
Cash and Cash Equivalents | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Cash and Cash Equivalents, at Carrying Value	0	0
Cash and Cash Equivalents | Decommisioning Fund Investments | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 0	$ 0

Financial Instruments And Inv51

Financial Instruments And Investments Transfers Between Levels (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
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