El Paso Electric 10-K 24 Feb 17 2016 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2016	Jan. 31, 2017	Jun. 30, 2016
Document and Entity Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
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		40,557,679
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 1,883,999,218

BALANCE SHEETS

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Utility plant:
Electric plant in service	$ 3,791,566	$ 3,616,301
Less accumulated depreciation and amortization	(1,244,332)	(1,329,843)
Net plant in service	2,547,234	2,286,458
Construction work in progress	154,738	293,796
Nuclear fuel; includes fuel in process of $57,315 and $51,854, respectively	194,842	190,282
Less accumulated amortization	(75,602)	(75,031)
Net nuclear fuel	119,240	115,251
Net utility plant	2,821,212	2,695,505
Current assets:
Cash and cash equivalents	8,420	8,149
Accounts receivable, principally trade, net of allowance for doubtful accounts of $2,156 and $2,046, respectively	88,452	66,326
Inventories, at cost	47,216	48,697
Under-collection of fuel revenues	11,123	0
Prepayments and other	8,988	9,872
Total current assets	164,199	133,044
Deferred charges and other assets:
Decommissioning trust funds	255,708	239,035
Regulatory assets	118,861	115,127
Other	16,298	17,896
Total deferred charges and other assets	390,867	372,058
Total assets	3,376,278	3,200,607
Capitalization:
Common stock, stated value $1 per share, 100,000,000 shares authorized, 65,685,615 and 65,709,819 shares issued, and 137,017 and 118,834 restricted shares, respectively	65,823	65,829
Capital in excess of stated value	322,643	320,073
Retained earnings	1,114,561	1,067,396
Accumulated other comprehensive loss, net of tax	(7,116)	(13,914)
Total stockholders' equity subtotal before treasury stock	1,495,911	1,439,384
Treasury stock, 25,304,914 and 25,384,834 shares, respectively, at cost	(421,515)	(422,846)
Common stock equity	1,074,396	1,016,538
Long-term debt, net of current portion	1,195,513	1,122,660	[1]
Total capitalization	2,269,909	2,139,198
Current liabilities:
Current maturities of long-term debt	83,143	0	[1]
Short-term borrowings under the revolving credit facility	81,574	141,738	[1]
Accounts payable, principally trade	62,953	59,978
Taxes accrued	32,488	30,351
Interest accrued	13,287	12,649
Over-collection of fuel revenues	255	4,023
Other	29,709	28,325
Total current liabilities	303,409	277,064
Deferred credits and other liabilities:
Accumulated deferred income taxes	555,066	495,237
Accrued pension liability	92,768	90,527
Accrued postretirement benefit liability	34,400	54,553
Asset retirement obligation	81,800	81,621
Regulatory liabilities	18,435	24,303
Other	20,491	38,104
Total deferred credits and other liabilities	802,960	784,345
Commitments and contingencies
Total capitalization and liabilities	$ 3,376,278	$ 3,200,607
[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.

BALANCE SHEETS (Parentheticals)

BALANCE SHEETS (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Nuclear fuel; fuel in process	$ 57,315	$ 51,854
Allowance for Doubtful Accounts Receivable, Current	$ 2,156	$ 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	65,685,615	65,709,819
Common Stock, Restricted Shares	137,017	118,834
Treasury Stock, Shares	25,304,914	25,384,834

STATEMENTS OF OPERATIONS

STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating revenues	$ 886,936	$ 849,869	$ 917,525
Energy expenses:
Fuel	173,738	188,400	251,005
Purchased and interchanged power	59,727	53,545	64,804
Cost of services, energy services	233,465	241,945	315,809
Operating revenues net of energy expenses	653,471	607,924	601,716
Other operating expenses:
Other operations	242,014	242,950	238,832
Maintenance	66,746	65,223	65,629
Depreciation and amortization	84,317	89,824	83,342
Taxes other than income taxes	65,533	63,736	62,750
Utilities operating expense	458,610	461,733	450,553
Operating income	194,861	146,191	151,163
Other income (deductions):
Allowance for equity funds used during construction	7,023	10,639	14,662
Investment and interest income, net	14,083	17,508	13,633
Miscellaneous non-operating income	1,292	2,062	4,075
Miscellaneous non-operating deductions	(3,699)	(4,328)	(4,199)
Nonoperating income (expense)	18,699	25,881	28,171
Interest charges (credits):
Interest on long-term debt and revolving credit facility	71,544	65,851	59,028
Other interest	1,303	1,313	1,250
Capitalized interest	(4,990)	(4,968)	(5,092)
Allowance for borrowed funds used during construction	(4,983)	(6,937)	(8,368)
Interest expense	62,874	55,259	46,818
Income before income taxes	150,686	116,813	132,516
Income tax expense	53,918	34,895	41,088
Net income	$ 96,768	$ 81,918	$ 91,428
Basic earnings per share	$ 2.390	$ 2.030	$ 2.270
Diluted earnings per share	2.390	2.030	2.270
Dividends declared per share of common stock	$ 1.225	$ 1.165	$ 1.105
Weighted average number of shares outstanding	40,350,688	40,274,986	40,190,991
Weighted average number of shares and dilutive potential shares outstanding	40,408,033	40,308,562	40,211,717

STATEMENTS OF COMPREHENSIVE OPE

STATEMENTS OF COMPREHENSIVE OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net income	$ 96,768	$ 81,918	$ 91,428
Unrecognized pension and post-retirement benefit costs:
Net gain (loss) arising during period	(20,053)	5,429	(54,328)
Prior service benefit	32,697	824	34,200
Reclassification adjustments included in net income for amortization of:
Prior service benefit	(7,407)	(6,574)	(7,659)
Net loss	4,965	8,622	6,182
Net unrealized gains/losses on marketable securities:
Net holding gains (losses) arising during period	8,444	(2,906)	10,827
Reclassification adjustments for net gains included in net income	(7,640)	(11,114)	(7,350)
Net losses on cash flow hedges:
Reclassification adjustment for interest expense included in net income	498	467	438
Total other comprehensive income (loss) before income taxes	11,504	(5,252)	(17,690)
Income tax benefit (expense) related to items of other comprehensive income (loss):
Unrecognized pension and post-retirement benefit costs	(4,261)	(3,286)	8,051
Net unrealized (gains) losses on marketable securities	(106)	2,828	(760)
Losses on cash flow hedges	(339)	(203)	(214)
Total income tax benefit (expense)	(4,706)	(661)	7,077
Other comprehensive income (loss), net of tax	6,798	(5,913)	(10,613)
Comprehensive income	$ 103,566	$ 76,005	$ 80,815

STATEMENTS OF CHANGES IN COMMON

STATEMENTS OF CHANGES IN COMMON STOCK EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss), Net of Tax	Treasury Stock
Balances at beginning of period (in shares) at Dec. 31, 2013		65,759,625				25,492,919
Balances at beginning of period at Dec. 31, 2013	$ 943,833	$ 65,760	$ 314,443	$ 985,665	$ 2,612	$ (424,647)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted common stock grants and deferred compensation (in shares)		103,672
Restricted common stock grants and deferred compensation	4,279	$ 104	4,175
Stock awards withheld for taxes (in shares)		(4,696)
Stock awards withheld for taxes	(188)	$ (5)	(183)
Forfeited restricted common stock (in shares)		(19,162)
Forfeited restricted common stock	(19)	$ (19)
Deferred taxes on stock incentive plan	(302)		(302)
Grants of share based compensation (in shares)		(10,104)
Grants of share based compensation	392	$ 10	382
Net income	91,428			91,428
Other comprehensive income (loss)	(10,613)				(10,613)
Dividends, Common Stock, Cash	(44,556)			(44,556)
Balances at end of period (in shares) at Dec. 31, 2014		65,849,543				25,492,919
Balances at end of period at Dec. 31, 2014	984,254	$ 65,850	318,515	1,032,537	(8,001)	$ (424,647)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted common stock grants and deferred compensation (in shares)		6,356
Restricted common stock grants and deferred compensation	3,829	$ 6	2,266
Stock Issued During Period, Shares, Treasury Stock Reissued						(93,455)
Stock Issued During Period, Value, Treasury Stock Reissued						$ 1,557
Stock awards withheld for taxes (in shares)		(15,031)
Stock awards withheld for taxes	(571)	$ (15)	(556)
Forfeited restricted common stock (in shares)		(12,215)				(871)
Forfeited restricted common stock	(26)	$ (12)				$ (14)
Deferred taxes on stock incentive plan	(475)		(475)
Grants of share based compensation (in shares)						(15,501)
Grants of share based compensation	581		323			$ 258
Net income	81,918			81,918
Other comprehensive income (loss)	(5,913)				(5,913)
Dividends, Common Stock, Cash	$ (47,059)			(47,059)
Balances at end of period (in shares) at Dec. 31, 2015	65,709,819	65,828,653				25,384,834
Balances at end of period at Dec. 31, 2015	$ 1,016,538	$ 65,829	320,073	1,067,396	(13,914)	$ (422,846)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted common stock grants and deferred compensation	$ 4,252		3,017
Stock Issued During Period, Shares, Treasury Stock Reissued	(188,005)					(74,181)
Stock Issued During Period, Value, Treasury Stock Reissued						$ 1,235
Stock awards withheld for taxes (in shares)		(5,723)
Stock awards withheld for taxes	$ (267)	$ (6)	(261)
Forfeited restricted common stock (in shares)		(298)				(197)
Forfeited restricted common stock	(3)					$ (3)
Deferred taxes on stock incentive plan	(364)		(364)
Grants of share based compensation (in shares)						(5,936)
Grants of share based compensation	277		178			$ 99
Net income	96,768			96,768
Other comprehensive income (loss)	6,798				6,798
Dividends, Common Stock, Cash	$ (49,603)			(49,603)
Balances at end of period (in shares) at Dec. 31, 2016	65,685,615	65,822,632				25,304,914
Balances at end of period at Dec. 31, 2016	$ 1,074,396	$ 65,823	$ 322,643	$ 1,114,561	$ (7,116)	$ (421,515)

Statements Of Cash Flows

Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 96,768	$ 81,918	$ 91,428
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of electric plant in service	84,317	89,824	83,342
Amortization of nuclear fuel	43,748	43,099	43,864
Deferred income taxes, net	50,510	30,846	39,129
Allowance for equity funds used during construction	(7,023)	(10,639)	(14,662)
Other amortization and accretion	17,295	17,707	18,380
Gain on sale of property, plant and equipment	(545)	(658)	(2,092)
Net gains on sale of decommissioning trust funds	(7,640)	(11,114)	(7,350)
Other operating activities	1,279	517	(93)
Change in:
Accounts receivable	(17,511)	4,839	(5,815)
Inventories	265	(2,859)	(786)
Net over-collection (under-collection) of fuel revenues	(14,891)	13,344	(3,121)
Prepayments and other	(1,184)	(3,984)	(2,750)
Accounts payable	(2,140)	(11,235)	9,684
Taxes accrued	1,945	4,512	(2,209)
Other current liabilities	2,022	3,719	1,198
Deferred charges and credits	(16,065)	(3,165)	(4,807)
Net cash provided by operating activities	231,150	246,671	243,340
Cash flows from investing activities:
Cash additions to utility property, plant and equipment	(225,361)	(281,458)	(277,078)
Cash additions to nuclear fuel	(42,383)	(41,966)	(37,877)
Capitalized interest and AFUDC:
Utility property, plant and equipment	(12,006)	(17,576)	(23,030)
Nuclear fuel	(4,990)	(4,968)	(5,092)
Allowance for equity funds used during construction	7,023	10,639	14,662
Decommissioning trust funds:
Purchases, including funding of $4.5 million	(99,497)	(110,223)	(117,675)
Sales and maturities	91,268	102,567	108,311
Proceeds from sale of property, plant, and equipment	4,841	721	2,395
Other investing activities	5,373	(470)	4,192
Net cash used for investing activities	(275,732)	(342,734)	(331,192)
Cash flows from financing activities:
Dividends paid	(49,603)	(47,059)	(44,556)
Borrowings under the revolving credit facility:
Proceeds	355,607	344,398	231,399
Payments	(415,771)	(217,192)	(231,219)
Payment on maturing RGRT senior notes	0	(15,000)	0
Proceeds from issuance of senior notes	157,052	0	149,468
Other financing activities	(2,432)	(1,439)	(2,328)
Net cash provided by financing activities	44,853	63,708	102,764
Net increase (decrease) in cash and cash equivalents	271	(32,355)	14,912
Cash and cash equivalents at beginning of period	8,149	40,504	25,592
Cash and cash equivalents at end of period	$ 8,420	$ 8,149	$ 40,504

Statements of Cash Flows Parent

Statements of Cash Flows Parenthetical - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Payments To Fund Decommissioning Fund	$ 4.5	$ 4.5	$ 4.5

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Significant Accounting Policies	Summary of Significant Accounting Policies General. El Paso Electric Company is a public utility engaged in the generation, transmission and distribution of electricity in an area of approximately 10,000 square miles in west Texas and southern New Mexico. The Company also serves a full requirements wholesale customer in Texas. Basis of Presentation . The Company maintains its accounts in accordance with the Uniform System of Accounts prescribed by the Federal Energy Regulatory Commission (the "FERC"). 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. Application of the Financial Accounting Standards Board (the "FASB" ) Guidance for Regulated Operations. Regulated electric utilities typically prepare their financial statements in accordance with the FASB guidance for regulated operations. The FASB guidance for regulated operations requires the Company to include an allowance for equity and borrowed funds used during construction ("AEFUDC" and "ABFUDC") as a cost of construction of electric plant in service. AEFUDC is recognized as income and ABFUDC is shown as capitalized interest charges in the Company’s statements of operations. The FASB guidance for regulated operations also requires the Company to show certain recoverable costs as either assets or liabilities on a utility’s balance sheet if the regulator provides assurance that these costs will be charged to and collected from the utility’s customers (or has already permitted such cost recovery) or will be credited or refunded to the utility’s customers. The resulting regulatory assets or liabilities are amortized in subsequent periods based upon the respective amortization periods reflected in a utility’s regulated rates. See Part II, Item 8, Financial Statements and Supplementary Data, Note D. The Company applies the FASB guidance for regulated operations for all three of the jurisdictions in which it operates. Comprehensive Income. Certain gains and losses that are not recognized currently in the statements of operations are reported as other comprehensive income in accordance with the FASB guidance for reporting comprehensive income. Utility Plant. Utility plant is generally reported at cost. The cost of renewals and betterments are capitalized and the costs of repairs and minor replacements are charged to the appropriate operating expense accounts. Depreciation is provided on a straight-line basis over the estimated remaining lives of the assets (ranging in average from 5 to 48 years). The average composite depreciation rate utilized in 2016 , 2015 and 2014 was 2.28% , 2.64% , and 2.60% , respectively. When property subject to composite depreciation is retired or otherwise disposed of in the normal course of business, its cost together with the cost of removal, less salvage is charged to accumulated depreciation. For other property dispositions, the applicable cost and accumulated depreciation is removed from the balance sheet accounts and a gain or loss is recognized. During 2016, depreciation and amortization decreased due to changes in depreciation rates approved in the most recent final orders from the Public Utility Commission of Texas ("PUCT") and the New Mexico Public Regulation Commission ("NMPRC") and changes in the estimated life of certain intangible software assets. See Part II, Item 8, Financial Statements and Supplementary Data, Note C and Note E. Previously, the Company recorded gains and losses on the disposition of vehicles in earnings when realized. However, beginning in 2016, the Company began crediting the proceeds (salvage) on the disposition of vehicles to accumulated depreciation. The cost of nuclear fuel is amortized to fuel expense on a units-of-production basis. The Company is also amortizing its share of costs associated with on-site spent fuel storage casks at Palo Verde Nuclear Generating Station ("Palo Verde") over the burn period of the fuel that will necessitate the use of the storage casks. See Part II, Item 8, Financial Statements and Supplementary Data, Note E. Impairment of Long-Lived Assets. Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated undiscounted future cash flows, an impairment charge is recognized for the amount by which the carrying amount of the asset exceeds the fair value of the asset. AFUDC and Capitalized Interest . The Company capitalizes interest ("ABFUDC") and common equity ("AEFUDC") costs to construction work in progress and capitalizes interest to nuclear fuel in process in accordance with the FERC Uniform System of Accounts as provided for in the FASB guidance. AFUDC is a non-cash component of income and is calculated monthly and charged to all new eligible construction and capital improvement projects. AFUDC is compounded on a semi-annual basis. The average AFUDC rates used in 2016 , 2015 and 2014 were 6.43% , 7.18% and 8.15% , respectively. Asset Retirement Obligation. The FASB guidance sets forth accounting requirements for the recognition and measurement of liabilities associated with the retirement of tangible long-lived assets. An ARO associated with long-lived assets included within the scope of the FASB guidance is that for which a legal obligation exists under enacted laws, statutes, written or oral contracts, including obligations arising under the doctrine of promissory estoppel and legal obligations to perform an asset retirement activity even if the timing and/or settlement are conditioned on a future event that may or may not be within the control of an entity. See Part II, Item 8, Financial Statements and Supplementary Data, Note F. Under the FASB guidance, these liabilities are recognized as incurred if a reasonable estimate of fair value can be established and are capitalized as part of the cost of the related tangible long-lived assets. The Company records the increase in the ARO due to the passage of time as an operating expense (accretion expense). Cash and Cash Equivalents . All temporary cash investments with an original maturity of three months or less are considered cash equivalents. Investments . The Company’s marketable securities, included in decommissioning trust funds in the balance sheet, are reported at fair value and consist of cash, equity securities and municipal, federal and corporate bonds in trust funds established for decommissioning of its interest in Palo Verde. Such marketable securities are classified as "available-for-sale" securities and, as such, unrealized gains and losses are included in accumulated other comprehensive loss as a separate component of common stock equity. However, if declines in the fair value of marketable securities below original cost basis are determined to be other than temporary, the declines are reported as losses in the statements of operations and a new cost basis is established for the affected securities at fair value. Gains and losses are determined using the cost of the security based on the specific identification basis. See Part II, Item 8, Financial Statements and Supplementary Data, Note O. Derivative Accounting. Accounting for derivative instruments and hedging activities requires the recognition of derivatives as either assets or liabilities in the balance sheet with measurement of those instruments at fair value. Any changes in the fair value of these instruments are recorded in earnings or other comprehensive income. See Part II, Item 8, Financial Statements and Supplementary Data, Note O. Inventories . Inventories, primarily parts, materials, supplies, fuel oil and natural gas are stated at average cost, which is not to exceed recoverable cost. Operating Revenues Net of Energy Expenses . The Company accrues revenues for services rendered, including unbilled electric service revenues. Energy expenses are stated at actual cost incurred. The Company’s Texas retail customers are billed under base rates and a fixed fuel factor approved by the PUCT. The Company’s New Mexico retail customers are billed under base rates and a fuel adjustment clause which is adjusted monthly, as approved by the NMPRC. The Company's FERC sales for resale customers are billed under formula base rates and fuel factors and a fuel adjustment clause which is adjusted monthly. The Company’s recovery of energy expenses is subject to periodic reconciliations of actual energy expenses incurred to actual fuel revenues collected. The difference between energy expenses incurred and fuel revenues charged to customers is reflected as over/under-collection of fuel revenues in the balance sheets. See Part II, Item 8, Financial Statements and Supplementary Data, Note C. Revenues. Revenues related to the sale of electricity are 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 customers 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 $21.0 million and $21.7 million as of December 31, 2016 and 2015 , respectively. The Company presents revenues net of sales taxes in its statements of operations. Allowance for Doubtful Accounts. The allowance for doubtful accounts represents the Company’s estimate of existing accounts receivable that will ultimately be uncollectible. The allowance is calculated by applying estimated write-off factors to various classes of outstanding receivables. The write-off factors used to estimate uncollectible accounts are based upon consideration of both historical collections experience and management’s best estimate of future collections success given the existing collections environment. Additions, deductions and balances for allowance for doubtful accounts for 2016 , 2015 and 2014 are as follows (in thousands): 2016 2015 2014 Balance at beginning of year $ 2,046 $ 2,253 $ 2,261 Additions: Charged to costs and expense 2,427 2,057 2,755 Recovery of previous write-offs 1,395 1,613 1,516 Uncollectible receivables written off 3,712 3,877 4,279 Balance at end of year $ 2,156 $ 2,046 $ 2,253 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 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 final orders from the PUCT and the NMPRC in its 2015 rate cases, effective January 1, 2016. See Part II, Item 8, Financial Statements and Supplementary Data, Note C 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 Part II, Item 8, Financial Statements and Supplementary Data, Note J. Earnings per Share . The Company’s restricted stock awards are participating securities and earnings per share must be calculated using the two-class method in both the basic and diluted earnings per share calculations. For the basic earnings per share calculation, net income is allocated to the weighted average number of restricted stock awards and to the weighted average number of shares outstanding. The net income allocated to the weighted average number of shares outstanding is then divided by the weighted average number of shares outstanding to derive the basic earnings per share. For the diluted earnings per share, net income is allocated to the weighted average number of restricted stock awards and to the weighted average number of shares and dilutive potential shares outstanding. The Company’s dilutive potential shares outstanding amount is calculated using the treasury stock method for the unvested performance shares. Net income allocated to the weighted average number of shares and dilutive potential shares is then divided by the weighted average number of shares and dilutive potential shares outstanding to derive the diluted earnings per share. See Part II, Item 8, Financial Statements and Supplementary Data, Note G. Stock-Based Compensation . The Company has a stock-based long-term incentive plan. The Company is required under the FASB guidance to measure the cost of employee services received in exchange for an award of equity instruments based on the grant-date fair value of the award. Such costs are recognized over the period during which an employee is required to provide service in exchange for the award (the "requisite service period") which typically is the vesting period. Compensation cost is not recognized for anticipated forfeitures prior to vesting of equity instruments. See Part II, Item 8, Financial Statements and Supplementary Data, Note G. Pension and Post-retirement Benefit Accounting. See Part II, Item 8, Financial Statements and Supplementary Data, Note M for a discussion of the Company’s accounting policies for its employee benefits. Reclassification. Certain amounts in the Company's financial statements for 2015 have been reclassified to conform to the 2016 presentation. The Company implemented Accounting Standards Update ("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 Part II, Item 8, Financial Statements and Supplementary Data, Note I and Note O for impact of ASU 2015-03, and Note J for impact of ASU 2015-17.

New Accounting Standards

New Accounting Standards	12 Months Ended
	Dec. 31, 2016
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Pronouncements and Changes in Accounting Principles	New Accounting Standards In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) to provide a framework that replaces the existing revenue recognition guidance, and has since modified the standard with several ASUs. The standard provides that an entity should recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. More specifically, the standard requires entities to recognize revenue through the application of a five-step model, which includes the: (i) identification of the contract; (ii) identification of the performance obligations; (iii) determination of the transaction price; (iv) allocation of the transaction price to the performance obligations; and (v) the recognition of revenue as the entity satisfies the performance obligations. Early adoption of ASU 2014-09 is permitted after December 15, 2016, however , the Company plans to adopt the new standard for reporting periods beginning after December 15, 2017. Under the new standard, companies may use either of the following transition methods: (i) a full retrospective approach reflecting the application of the standard in each prior reporting period with the option to elect certain practical expedients, or (ii) a modified retrospective approach with the cumulative effect of initially adopting ASU 2014-09 recognized at the date of adoption (which includes additional footnote disclosures). The Company has not concluded which transition method it will elect but it currently anticipates using the modified retrospective approach. The Company is currently in the process of evaluating the impact of the new standard on its various revenue and cash flow streams, including the evaluation of the impact, if any, on changes to business processes, systems and controls to support recognition and disclosure under the new guidance. Tariff sales to customers are determined to be in the scope of the new standard and represent a significant portion of the Company’s total operating revenues. The Company has not completed its final evaluation of tariff sales under the new guidance but currently does not anticipate that ASU 2014-09 will have a material impact on the Company's revenue recognition for such sales. The Company is still considering the impacts of the guidance on several industry-related accounting issues, including the accounting for contributions in aid of construction ("CIAC"), assessing the collectability criterion and the presentation of revenues associated with alternative revenue programs. The Company's initial assessment may change as we execute our implementation plan and new guidance is provided by the American Institute of Certified Public Accountants Power and Utilities Industry Task Force. In January 2016, the FASB issued ASU 2016-01, Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Liabilities to enhance the reporting model for financial instruments by addressing certain aspects of recognition, measurement, presentation, and disclosure. ASU 2016-01 generally requires entities to measure equity investments that do not result in consolidation and are not accounted for under the equity method at fair value and recognize any changes in fair value in net income. The guidance for classifying and measuring investments in debt securities and loans is not changed by this ASU, but requires entities to record changes in other comprehensive income. Financial assets and financial liabilities must be separately presented by measurement category on the balance sheet or in the accompanying notes to the financial statements. ASU 2016-01 clarifies the need for a valuation allowance on a deferred tax asset related to available-for-sale securities in combination with the entity's other deferred tax assets. The provisions of this ASU become effective for public companies for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Upon adoption of the new standard, the Company expects to record the cumulative effects as of January 1, 2018 which will result in an adjustment to accumulated other comprehensive income (losses) and retained earnings for unrealized gains (losses) related to equity securities owned by the Company. Had the Company been required to adopt the new standard at January 1, 2016, accumulated other comprehensive income would decrease by $28.8 million and retained earnings would increase by a corresponding amount. Furthermore, the Company would report for the year ended December 31, 2016 an increase in investment income of $1.2 million , an increase in income tax expense of $0.2 million and a decrease in other comprehensive income of $1.0 million . The Company is continuing to assess the future impact of this ASU. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) to increase transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and requiring qualitative and quantitative disclosures on leasing agreements. ASU 2016-02 maintains a distinction between finance leases and operating leases similar to the distinction under previous leases guidance for capital leases and operating leases. The impact of leases reported in the Company's operating results and statement of cash flows are expected to be similar to previous GAAP. ASU 2016-02 requires the recognition in the statement of financial position, by the lessee, of a liability to make lease payments (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 guidance. The lessee is permitted to make an accounting policy election to not recognize lease assets and lease liabilities for short-term leases. Implementation of the standard 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, however, the Company plans to adopt the new standard for reporting periods beginning after December 15, 2018. Adoption of the new lease accounting standard will require the Company to apply the new standard to the earliest period using a modified retrospective approach. The Company is currently in the process of evaluating the impact of the new standard, including the evaluation of the impact, if any, on changes to business processes, systems and controls to support recognition and disclosure under the new guidance, however, at this time is unable to determine the impact this standard will have on the financial statements and related disclosures. In 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. The Company will adopt the new standard effective January 1, 2017 and does not expect the effect of the adoption to be material to the Company's financial condition, results of operations or cash flows. The cumulative effect of the adoption of the new standard will be to increase net operating loss carryforward deferred tax assets and retained earnings by approximately $0.2 million on January 1, 2017 . The Company also expects to continue to account for its outstanding stock awards based on the equity method and therefore does not anticipate any changes in reporting related compensation expense. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326) ("ASU 2016-13"). ASU 2016-13 changes how companies measure and recognize credit impairment for many financial assets. The new current expected credit loss model will require companies to immediately recognize an estimate of credit losses expected to occur over the remaining life of the financial assets that are in the scope of the standard. The ASU also makes targeted amendments to the current impairment model for available-for-sale debt securities. 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 ASU 2016-13. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230) Classification of Certain Cash Receipts and Cash Payments to reduce diversity in practice in how certain cash receipts and cash payments are classified in the statement of cash flows. The 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. In December 2016, the FASB issued ASU 2016-19, Technical Corrections and Improvements, which amends a number of Topics in the FASB ASC. This ASU is part of an ongoing FASB project to facilitate Codification updates for non-substantive technical corrections, clarifications, and improvements that are not expected to have a significant effect on accounting practice or create a significant administrative cost to most entities. Most of the amendments are effective upon issuance of ASU 2016-19 while certain amendments that require transition guidance are effective for the Company beginning January 1, 2017. The Company believes it is in compliance with those amendments that are effective immediately and that are applicable to the Company. The Company has not completed its evaluation of the new standard for amendments that require transition guidance.

Regulation

Regulation	12 Months Ended
	Dec. 31, 2015
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 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 (the "2015 Texas Retail Rate Case"). On July 21, 2016, the parties to PUCT Docket No. 44941 filed the Joint Motion to Implement Uncontested Amended and Restated Stipulation and Agreement which was unopposed by the parties (the "Unopposed Settlement"). On August 25, 2016, the PUCT approved the Unopposed Settlement and issued its final order in Docket No. 44941 (the "PUCT Final Order"), as proposed. The PUCT Final Order provided for: (i) an annual non-fuel base rate increase, lower annual depreciation expense, a revised return on equity for AFUDC purposes, and the inclusion of substantially all new plant in service in rate base; (ii) an additional annual non-fuel base rate increase of $3.7 million related to Four Corners Generating Station ("Four Corners") costs, which will be collected through a surcharge terminating on July 12, 2017; (iii) removing the separate rate treatment for residential customers with solar systems that the Company had proposed in its August 10, 2015 filing; (iv) allowing the Company to recover $3.1 million in rate case expenses through a separate surcharge and (v) allowing the Company to recover revenues associated with the relate back of rates to consumption on and after January 12, 2016 through March 31, 2016 through a separate surcharge. Interim rates, associated with the annual non-fuel base rate increase, became effective on April 1, 2016. The additional surcharges associated with the incremental Four Corners costs, rate case expenses and the relate back of rates to consumption on and after January 12, 2016 through March 31, 2016 were implemented on October 1, 2016. For financial reporting purposes, the Company deferred any recognition of the Company's request in its 2015 Texas Retail Rate Case until it received the PUCT Final Order on August 25, 2016. Accordingly, it reported in the third quarter of 2016 the cumulative effect of the PUCT Final Order which related back to January 12, 2016. 2017 Texas Retail Rate Case Filing. On February 13, 2017, the Company filed with the City of El Paso, other municipalities incorporated in the Company's Texas service territory and the PUCT in Docket No.46831, a request for an increase in non-fuel base revenues of approximately $42.5 million . The Company invoked its statutory right to have its new rates relate back for consumption on and after July 18, 2017, which is the 155th day after the filing. The difference in rates that would have been billed will be surcharged or refunded to customers after the PUCT 's final order in Docket No. 46831 . The PUCT has the authority to require the Company to surcharge or refund such difference over a period not to exceed 18 months. The Company cannot predict the outcome or the timing of this rate case at this time. Energy Efficiency Cost Recovery Factor. On May 1, 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 included a performance bonus of $1.0 million . The Company recorded the performance bonus in operating revenues 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 $0.7 million 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, filed a settlement in the case that approved the Company's proposal with a reduction to the 2015 program bonus of $0.2 million . The PUCT approved the settlement on October 28, 2016. The settlement approved by the PUCT included a performance bonus of $0.5 million which was recorded in operating revenues 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. On November 30, 2016, the Company filed a request, which was assigned PUCT Docket No. 46610, to increase its fixed fuel factor by approximately 28.8% to reflect increased fuel expenses primarily related to an increase in the price of natural gas used to generate power. The increase in the fixed fuel factor was effective on an interim basis January 1, 2017 and approved by the PUCT on January 10, 2017. As of December 31, 2016, the Company had under-recovered fuel costs in the amount of $11.1 million for the Texas jurisdiction. Fuel Reconciliation Proceeding . On September 27, 2016, the Company filed an application with the PUCT, designated as PUCT Docket No. 46308, to reconcile $436.6 million of Texas fuel and purchased power expenses incurred during the period of April 1, 2013 through March 31, 2016. A procedural schedule has been adopted with hearings in April 2017. As of December 31, 2016, Texas jurisdictional fuel and purchased power costs subject to a future Texas fuel reconciliation are approximately $114.4 million . The Company cannot predict the outcome or the timing of this matter. Montana Power Station Approvals. The Company received Certificate of Convenience and Necessity ("CCN") approval 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 that includes the 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. The Company expects completion of the solar facility and commencement of the program in the second quarter of 2017. Four Corners . On February 17, 2015, the Company and Arizona Public Service Company (" APS ") entered into an asset purchase agreement ( the " Purchase and Sale Agreement ") providing for the sale of the Company's interest in Four Corners to APS. The sale of the Company's interest in Four Corners closed on July 6, 2016 . See Part II, Item 8, Financial Statements and Supplementary Data, Note E 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 a rate case proceeding. On September 1, 2016, a motion by parties in the proceeding to suspend the procedural schedule in order to pursue settlement was approved, and the parties are engaged in settlement discussions. At December 31, 2016, the regulatory asset associated with the Four Corners mine reclamation costs for the Company's Texas jurisdiction was approximately $7.3 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 the Company's 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 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 a request with the NMPRC, in Case No. 15-00127-UT, for an annual increase in non-fuel base rates. On June 8, 2016, the NMPRC issued its final order in Case No. 15-00127-UT (the "NMPRC Final Order") which approved an annual increase in non-fuel base rates of approximately $0.6 million , an increase of approximately $0.5 million in other service fees and a decrease in the Company's allowed return on equity to 9.48% . The NMPRC Final Order concluded that all of the Company's new plant in service was reasonable and necessary and therefore would be recoverable in rates. The Company's rates were approved by the NMPRC effective July 1, 2016 and implemented at such time. 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 in Case No. 15-00127-UT, fuel and purchased power costs are no longer recovered through base rates but are 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. The Company's request to reconcile its fuel and purchased power costs for the period January 1, 2013 through December 31, 2014 was approved in Case No. 15-00127-UT. New Mexico jurisdictional costs subject to prudence review are costs from January 1, 2015 through December 31, 2016 that total approximately $114.6 million . At December 31, 2016, the Company had a net fuel over-recovery balance of $0.2 million in New Mexico . Montana Power Station Approvals. The Company received CCNs 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 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. Four Corners. On June 15, 2016, in NMPRC Case No. 15-00109-UT, the NMPRC issued its final order approving the Company's sale and abandonment of its ownership interest in Four Corners to APS pursuant to a February 17, 2015 Purchase and Sale Agreement between the Company and APS. See Part II, Item 8, Financial Statements and Supplementary Data, Note E for further details on the sale of Four Corners. 5 MW Holloman Air Force Base ("HAFB") Facility CCN. On October 7, 2015, in NMPRC Case No. 15-00185-UT, the NMPRC issued a final order approving a CCN for a 5 MW solar power generation facility located on HAFB in the Company's service territory in New Mexico. The Company and HAFB negotiated a special retail contract, which includes power sales agreement for the facility, to replace the existing load retention agreement which was approved by final order issued October 5, 2016 in NMPRC Case No. 16-00224-UT. Construction of the solar generation facility is expected to be completed in the 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 $310.0 million of new long-term debt and to guarantee the issuance of up to $65.0 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 $150.0 million 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 $150.0 million was previously issued on December 1, 2014 , for a total principal amount outstanding of $300.0 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 sale of the Company's interest in Four Corners closed on July 6, 2016 . See Part II, Item 8, Financial Statements and Supplementary Data, Note E for further details on the sale of Four Corners. 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 the revolving credit facility (" RCF ") up to $400.0 million outstanding at any time, to issue up to $310.0 million in long-term debt, and to guarantee the issuance of up to $65.0 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 $150.0 million aggregate principal amount of 5.00% Senior Notes due December 1, 2044 . Additionally under this authorization, on January 9, 2017, the Company exercised its option to extend the maturity of the RCF by one year to January 14, 2020 and to increase the size of the facility by $50.0 million to $350.0 million . The Company still has the option to extend the facility by one additional year to January 2021 and to increase the RCF by up to $50.0 million (up to a total of $400.0 million ) upon the satisfaction of certain conditions, more fully set forth in the agreement, including obtaining commitments from lenders or third party financial institutions. Additionally, the Company agreed to reduce the letters of credit commitment to $50.0 million from a total commitment, under the RCF, of $350.0 million . Other Required Approvals. The Company has obtained required approvals for rates and tariffs, securities transactions and other approvals as required by the FERC. United States Department of Energy ("DOE"). The DOE regulates the Company's exports of power to the Comisión Federal de Electricidad in Mexico pursuant to a license and two presidential permits issued by the DOE. The DOE is authorized to assess operators of nuclear generating facilities a share of the costs of decommissioning the DOE's uranium enrichment facilities and for the ultimate costs of disposal of spent nuclear fuel. See Part II, Item 8, Financial Statements and Supplementary Data, Note E for discussion of spent fuel storage and disposal costs. Sales for Resale The Company provides firm capacity and associated energy to the Rio Grande Electric Cooperative ("RGEC") pursuant to an ongoing contract with a two-year notice to terminate provision. The Company also provides network integrated transmission service to the RGEC pursuant to the Company's Open Access Transmission Tariff ("OATT"). The contract includes a formula-based rate that is updated annually to recover non-fuel generation costs and a fuel adjustment clause designed to recover all eligible fuel and purchased power costs allocable to the RGEC.

Regulatory Assets and Liabiliti

Regulatory Assets and Liabilities	12 Months Ended
	Dec. 31, 2016
Regulatory Assets and Liabilities Disclosure [Abstract]
Schedule of Regulatory Assets and Liabilities	Regulatory Assets and Liabilities The Company's operations are regulated by the PUCT, the NMPRC and the FERC. Regulatory assets represent probable future recovery of previously incurred costs, which will be collected from customers through the ratemaking process. Regulatory liabilities represent probable future reductions in revenues associated with amounts that are to be credited to customers through the ratemaking process. Regulatory assets and liabilities reflected in the Company's balance sheet are presented below (in thousands): Amortization Period Ends December 31, 2016 December 31, 2015 Regulatory assets Regulatory tax assets (a) (b) $ 66,670 $ 69,359 Loss on reacquired debt (c) May 2035 15,780 16,632 Final coal reclamation (d) (e) 9,581 9,520 Nuclear fuel postload daily financing charge (e) 3,831 4,195 Unrecovered issuance costs due to reissuance of PCBs (c) August 2042 794 827 Texas energy efficiency (f) — 25 Texas 2015 rate case costs September 2018 2,670 1,882 Texas 2017 rate case costs (g) 246 — Texas relate back surcharge (h) 6,455 — New Mexico renewable energy credits and related costs (i) June 2022 6,937 6,397 New Mexico 2010 FPPCAC audit June 2019 398 434 New Mexico Palo Verde deferred depreciation (b) 4,415 4,568 New Mexico 2015 rate case costs June 2019 1,074 1,288 New Mexico 2017 rate case costs (g) 10 — Total regulatory assets $ 118,861 $ 115,127 Regulatory liabilities Regulatory tax liabilities (a) (b) $ 10,648 $ 17,266 Accumulated deferred investment tax credit (j) (b) 3,328 4,011 Texas energy efficiency (f) 1,288 — New Mexico energy efficiency (f) 2,159 2,238 Texas military base discount and recovery factor (k) 184 788 New Mexico gain on sale of assets (l) June 2019 828 — Total regulatory liabilities $ 18,435 $ 24,303 ______________________________ (a) We do not earn a return on these items since the related accumulated deferred income tax assets and liabilities offset. (b) The amortization periods for these assets and liabilities are based upon the life of the associated assets or liabilities. (c) This item is recovered as a component of the weighted cost of debt and amortized over the life of the related debt issuance. (d) This item relates to coal reclamation costs associated with Four Corners. See Part II, Item 8, Financial Statements and Supplementary Data, Note C. (e) This item is recovered through fuel recovery mechanisms established by tariffs. (f) This item is recovered or credited through a recovery factor that is set annually. (g) Amortization period is anticipated to be established in next general rate case. (h) This item relates to the recovery of revenues through a separate surcharge beginning October 1, 2016 and ending September 30, 2017. See Part II, Item 8, Financial Statements and Supplementary Data, Note C. (i) This item relates to renewable energy credits and procurement plan costs, components approved for recovery in the New Mexico 2015 rate case. (j) This item is excluded from rate base. (k) This item represents the net asset/net liability related to the military discount which is recovered from non-military customers through a recovery factor that is set annually. (l) This item relates to the gains on the sales of assets the Company shares with its New Mexico customers over a three year period.

Utility Plant, Palo Verde and O

Utility Plant, Palo Verde and Other Jointly-Owned Utility Plant	12 Months Ended
	Dec. 31, 2016
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Schedule of Public Utility Property, Plant, and Equipment	Utility Plant, Palo Verde and Other Jointly-Owned Utility Plant The table below presents the balance of each major class of depreciable assets at December 31, 2016 (in thousands): Gross Plant Accumulated Depreciation Net Plant Nuclear production $ 948,382 $ (320,000 ) $ 628,382 Steam and other 926,419 (186,539 ) 739,880 Total production 1,874,801 (506,539 ) 1,368,262 Transmission 498,660 (259,488 ) 239,172 Distribution 1,127,897 (365,601 ) 762,296 General 205,866 (57,240 ) 148,626 Intangible 84,342 (55,464 ) 28,878 Total $ 3,791,566 $ (1,244,332 ) $ 2,547,234 During 2016, depreciation decreased due to changes in rates approved in the PUCT Final Order and the NMPRC Final Order. The change, effective in January 2016 for Texas and July 2016 for New Mexico, reduced depreciation expense in 2016 by $10.9 million . Amortization of intangible plant (software) is provided on a straight-line basis over the estimated useful life of the asset (ranging from 3 to 15 years). Effective July 2015, the Company changed the estimated useful life of certain large intangible software systems which decreased depreciation during 2015 by $1.8 million . The table below presents the actual and estimated amortization expense for intangible plant for the previous three years and for the next five years (in thousands): 2014 $ 8,051 2015 6,482 2016 5,302 2017 (estimated) 5,148 2018 (estimated) 4,631 2019 (estimated) 4,242 2020 (estimated) 3,808 2021 (estimated) 3,227 The Company owns a 15.8% interest in each of the three nuclear generating units and common facilities at Palo Verde, in Wintersburg, Arizona. The Palo Verde Participants include the Company and six other utilities: APS, Southern California Edison Company ("SCE"), PNM, Southern California Public Power Authority, Salt River Project Agricultural Improvement and Power District ("SRP") and the Los Angeles Department of Water and Power. A summary of the Company’s investment in jointly-owned utility plant, excluding fuel inventories, at December 31, 2016 and 2015 is as follows (in thousands): December 31, 2016 December 31, 2015 Palo Verde Other (a) Palo Verde Other (a) Electric plant in service $ 948,382 $ 67,621 $ 917,483 $ 229,627 Accumulated depreciation (320,000 ) (44,377 ) (304,060 ) (181,886 ) Construction work in progress 50,598 1,895 48,938 9,528 Total $ 678,980 $ 25,139 $ 662,361 $ 57,269 _______________ (a) 2015 other jointly-owned utility plant includes a 7% interest in Units 4 and 5 at Four Corners and certain other transmission facilities which the Company sold on July 6, 2016. Palo Verde The operation of Palo Verde and the relationship among the Palo Verde Participants is governed by the Arizona Nuclear Power Project Participation Agreement (the "ANPP Participation Agreement"). APS serves as operating agent for Palo Verde, and under the ANPP Participation Agreement, the Company has limited ability to influence operations and costs at Palo Verde. Pursuant to the ANPP Participation Agreement, the Palo Verde Participants share costs and generating entitlements in the same proportion as their percentage interests in the generating units, and each participant is required to fund its share of fuel, other operations, maintenance and capital costs. The Company’s share of direct expenses in Palo Verde and other jointly-owned utility plants is reflected in fuel expense, other operations expense, maintenance expense, miscellaneous other deductions, and taxes other than income taxes in the Company’s statements of operations. The ANPP Participation Agreement provides that if a participant fails to meet its payment obligations, each non-defaulting participant shall pay its proportionate share of the payments owed by the defaulting participant. Because it is impracticable to predict defaulting participants, the Company cannot estimate the maximum potential amount of future payment, if any, which could be required under this provision. Nuclear Regulatory Commission . The Nuclear Regulatory Commission ("NRC") regulates the operation of all commercial nuclear power reactors in the United States, including Palo Verde. The NRC periodically conducts inspections of nuclear facilities and monitors performance indicators to enable the agency to arrive at objective conclusions about a licensee’s safety performance. Palo Verde Operating Licenses. Operation of each of the three Palo Verde Units requires an operating license from the NRC. The NRC issued full power operating licenses for Unit 1 in June 1985, Unit 2 in April 1986 and Unit 3 in November 1987 and issued renewed operating licenses for each of the three units in April 2011, which extended the licenses for Units 1, 2 and 3 to June 2045, April 2046 and November 2047, respectively. Decommissioning . Pursuant to the ANPP Participation Agreement and federal law, the Company funds its share of the estimated costs to decommission Palo Verde Units 1, 2 and 3, including the Common Facilities, through the term of their respective operating licenses and is required to maintain a minimum accumulation and funding level in its decommissioning account at the end of each annual reporting period during the life of the plant. The Company has established external trusts with an independent trustee, which enables the Company to record a current deduction for federal income tax purposes for most of the amounts funded. At December 31, 2016 , the Company’s decommissioning trust fund had a balance of $255.7 million , which is above its minimum funding level. The Company monitors the status of its decommissioning funds and adjusts its deposits, if necessary. Decommissioning costs are estimated every three years based upon engineering cost studies performed by outside engineers retained by APS. In December 2013, the Palo Verde Participants approved the 2013 Palo Verde decommissioning study (the "2013 Study"). The 2013 Study estimated that the Company must fund approximately $380.7 million (stated in 2013 dollars) to cover its share of decommissioning costs which was an increase in decommissioning costs of $23.3 million (stated in 2013 dollars) from the 2010 Palo Verde decommissioning study. However, because the cash flows from the 2013 Study were less than the inflated amounts from the 2010 Study, the effect of this change lowered the ARO by $1.9 million which lowered annual expenses starting in January 2014. Although the 2013 Study was based on the latest available information, there can be no assurance that decommissioning cost estimates will not increase in the future or that regulatory requirements will not change. In addition, until a new low-level radioactive waste repository opens and operates for a number of years, estimates of the cost to dispose of low-level radioactive waste are subject to uncertainty. As provided in the ANPP Participation Agreement, the participants are required to conduct a new decommissioning study every three years . A 2016 Palo Verde decommissioning study (the "2016 Study") is underway and is expected to be finalized in the second quarter of 2017 at which time the Company will record its effects. If the expected cash flows as identified in the 2016 Study exceed the expected cash flows identified in the 2013 Study (stated in 2016 dollars), the ARO will increase with a corresponding increase in the ARO asset. Under such circumstances, increases in Palo Verde accretion expense and depreciation expense will occur. While the Company attempts to seek amounts in rates to meet its decommissioning obligations, it is not able to conclude given the evidence available to it now that it is probable these costs will continue to be collected over the period until decommissioning begins in 2044. The Company is ultimately responsible for these costs and its future actions combined with future decisions from regulators will determine how successful the Company is in this effort. Spent Nuclear Fuel and Waste Disposal . Pursuant to the Nuclear Waste Policy Act of 1982, as amended in 1987 (the "NWPA"), 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 refunded 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. After June 2015, APS will file annual claims for the period July 1 of the then-previous year to June 30 of the then-current year. On November 2, 2015, APS filed a $12.0 million claim for the period July 1, 2014 through June 30, 2015. In February 2016, the DOE notified APS of the approval of the claim. 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 . On February 1, 2017, the DOE notified APS of the approval of the claim. Any reimbursement is anticipated to be received in the second quarter of 2017, and the majority of the award received by the Company will be credited to customers through applicable fuel adjustment clauses. DOE’s Construction Authorization Application for Yucca Mountain. The DOE had planned to meet its disposal obligations by designing, licensing, constructing and operating a permanent geologic repository in Yucca Mountain, Nevada. In March 2010, the DOE filed a motion to dismiss with prejudice its Yucca Mountain construction authorization application that was pending before the NRC. Several interested parties have intervened in the NRC proceeding, and the proceeding has not been conclusively decided by the NRC or the courts. The Company cannot predict when spent fuel shipments to the DOE will commence. Palo Verde has sufficient capacity at its on-site independent spent fuel storage installation (“ISFSI”) to store all of the nuclear fuel that will be irradiated during the initial operating license period, which ends in December 2027. Additionally, Palo Verde has sufficient capacity at its on-site ISFSI to store a portion of the fuel that will be irradiated during the period of extended operation, which ends in November 2047. If uncertainties regarding the United States government’s obligation to accept and store spent fuel are not favorably resolved, APS will evaluate alternative storage solutions that may obviate the need to expand the ISFSI to accommodate all of the fuel that will be irradiated during the period of extended operation. Liability and Insurance Matters . The Palo Verde Participants have insurance for public liability resulting from nuclear energy hazards to the full limit of liability under federal law, which is currently at $13.4 billion . This potential liability is covered by primary liability insurance provided by commercial insurance carriers in the amount of $450.0 million , and the balance is covered by an industry-wide retrospective assessment program. If a loss at a nuclear power plant covered by the programs exceeds the accumulated funds in the primary level of protection, the Company could be assessed retrospective premium adjustments on a per incident basis. Under federal law, the maximum assessment per reactor under the program for each nuclear incident is approximately $127.3 million , subject to an annual limit of $19.0 million . Based upon the Company's 15.8% interest in the three Palo Verde units, the Company's maximum potential assessment per incident for all three units is approximately $60.4 million , with an annual payment limitation of approximately $9.0 million . The Palo Verde Participants maintain $2.75 billion of "all risk" nuclear property insurance. The insurance provides coverage for property damage and decontamination at Palo Verde. For covered incidents involving property damage not accompanied by a release of radioactive material, the policy's coverage limit is $2.25 billion . The Company has also secured insurance against portions of any increased cost of generation or purchased power and business interruption resulting from a sudden and unforeseen outage of any of the three units. The insurance coverage discussed in this and the previous paragraph is subject to certain policy conditions and exclusions. A mutual insurance company whose members are utilities with nuclear facilities issues these policies. If losses at any nuclear facility covered by this mutual insurance company were to exceed the accumulated funds for these insurance programs, the Company could be assessed retrospective premium adjustments of up to $12.9 million for the current policy period. Four Corners On February 17, 2015, the Company and APS entered into the Purchase and Sale Agreement providing for the sale of the Company’s interests in Four Corners to APS. Four Corners continued to provide energy to serve the Company's native load up to the closing date of the sale on July 6, 2016 . Also on July 6, 2016, prior to the closing of the transaction, the Company and APS entered into an amendment to the Purchase and Sale Agreement pursuant to which APS assigned its right, title and interest in the Purchase and Sale Agreement to its affiliate 4C Acquisition, LLC ("APS's affiliate"), and Pinnacle West Capital Corporation, the parent company of APS and APS's affiliate ("Pinnacle West"), guaranteed APS's affiliate's obligations under the Purchase and Sale Agreement. The sales price was $32.0 million , which was 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 the assumption by APS's affiliate 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's affiliate. At the closing, the Company received approximately $4.2 million in cash, subject to post-closing adjustments. No significant gain or loss was recorded after the closing date. APS's affiliate assumed responsibility for all Four Corners capital expenditures made after July 6, 2016, which assumption is guaranteed by Pinnacle West. In addition, APS's affiliate will indemnify the Company against certain liabilities and costs related to the future operation of Four Corners, which indemnification is guaranteed by Pinnacle West. See Part II, Item 8, Financial Statements and Supplementary Data, Note C for a discussion of regulatory filings associated with Four Corners.

Accounting for Asset Retirement

Accounting for Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2016
Accounting for Asset Retirement Obligations
Asset Retirement Obligation Disclosure	Accounting for Asset Retirement Obligation The Company complies with the FASB guidance for ARO. This guidance affects the accounting for the decommissioning of Palo Verde and the method used to report the decommissioning obligation. The Company also complies with the FASB guidance for conditional ARO which primarily affects the accounting for the disposal obligations of the Company’s fuel oil storage tanks, water wells, evaporative ponds and asbestos found at the Company’s gas-fired generating plants. The Company’s ARO are subject to various assumptions and determinations such as: (i) whether a legal obligation exists to remove assets; (ii) estimation of the fair value of the costs of removal; (iii) when final removal will occur; (iv) future changes in decommissioning cost escalation rates; and (v) the credit-adjusted interest rates to be utilized in discounting future liabilities. Changes that may arise over time with regard to these assumptions and determinations will change amounts recorded in the future as an expense for ARO. The Company records the increase in the ARO due to the passage of time as an operating expense (accretion expense). If the Company incurs or assumes any liability in retiring any asset at the end of its useful life without a legal obligation to do so, it will record such retirement costs as incurred. The ARO liability for Palo Verde is based upon the estimated cost of decommissioning the plant from the 2013 Palo Verde decommissioning study. See Part II, Item 8, Financial Statements and Supplementary Data, Note E. The ARO liability is calculated by adjusting the estimated decommissioning costs for spent fuel storage and a profit margin and market-risk premium factor. The resulting costs are escalated over the remaining life of the plant and finally discounted using a credit-risk adjusted discount rate. As Palo Verde approaches the end of its estimated useful life, the difference between the ARO liability and future current cost estimates will narrow over time due to the accretion of the ARO liability. Because the DOE is obligated to assume responsibility for the permanent disposal of spent fuel, spent fuel costs have not been included in the ARO calculation. The Company maintains six external trust funds with an independent trustee that are legally restricted to settling its ARO at Palo Verde. The fair value of the funds at December 31, 2016 is $255.7 million . The FASB guidance requires the Company to revise its previously recorded ARO for any changes in estimated cash flows including changes in estimated probabilities related to timing of settlements. Any changes that result in an upward revision to estimated cash flows shall be treated as a new liability. Any downward revisions to the estimated cash flows result in a reduction to the previously recorded ARO. In December 2013, the Company implemented the 2013 Palo Verde decommissioning study, and as a result, revised its ARO related to Palo Verde to decrease its estimated cash flows from the 2010 Study to the 2013 Study (see Part II, Item 8, Financial Statements and Supplementary Data, Note E). The assumptions used to calculate the Palo Verde ARO liability are as follows: Escalation Rate Credit-Risk Adjusted Discount Rate Original ARO liability 3.60 % 9.50 % Incremental ARO liability 3.60 % 6.20 % An analysis of the activity of the Company’s total ARO liability from January 1, 2014 through December 31, 2016 , including the effects of each year’s estimate revisions, is presented below. In 2016, the settled liabilities reflect the sale of the Company's interest in Four Corners including the related ARO. In 2014, the estimate revision includes an adjustment to Four Corners due to the early recognition of the obligation resulting from the Purchase and Sale Agreement with APS. 2016 2015 2014 ARO liability at beginning of year $ 81,621 $ 74,577 $ 65,214 Liabilities incurred — 189 — Liabilities settled (6,993 ) — — Revisions to estimate — — 3,561 Accretion expense 7,172 6,855 5,802 ARO liability at end of year $ 81,800 $ 81,621 $ 74,577 The Company has transmission and distribution lines which are operated under various property easement agreements. If the easements were to be released, the Company may have a legal obligation to remove the lines; however, the Company has assessed the likelihood of this occurring as remote. The majority of these easements include renewal options which the Company routinely exercises. The amount of cost of removal collected in rates for non-legal liabilities has not been material.

Common Stock (Notes)

Common Stock (Notes)	12 Months Ended
	Dec. 31, 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 Overview The Company’s common stock has a stated value of $1 per share, with no cumulative voting rights or preemptive rights. Holders of the common stock have the right to elect the Company’s directors and to vote on other matters. Long-Term Incentive Plan On May 29, 2014 , the Company’s shareholders approved an amended and restated stock-based long-term incentive plan (the "Amended and Restated 2007 LTIP") and authorized the issuance of up to 1.7 million shares of the Company's common stock for the benefit of directors and employees. Under the Amended and Restated 2007 LTIP, shares of the Company's common stock may be issued through the award or grant of non-statutory stock options, incentive stock options, stock appreciation rights, restricted stock, bonus stock, performance stock, cash-based awards and other stock-based awards. The Company may issue new shares, purchase shares on the open market, or issue shares from shares of the Company's common stock the Company has repurchased to meet the share requirements of the Amended and Restated 2007 LTIP. Beginning in 2015, shares of the Company's common stock issued for employee benefit and stock incentive plans have been issued from the shares repurchased and held in treasury stock. As discussed in Part II, Item 8, Financial Statements and Supplementary Data, Note A, the Company accounts for its stock-based long-term incentive plan under the FASB guidance for stock-based compensation. Restricted Stock with Service Condition and Other Stock-Based Awards . The Company has awarded restricted stock and other stock-based awards under its long-term incentive plan. Restrictions from resale on restricted stock awards generally lapse and awards vest over periods of one to three years. The market value of the unvested restricted stock at the date of grant is amortized to expense over the restriction period net of anticipated forfeitures. Other stock-based awards are fully vested and are expensed at fair value on the date of grant. Previously directors could elect to receive retainers and meeting fees in cash, restricted stock, or a combination of cash and stock. On May 29, 2014 , the Board of Directors voted to revise the terms of the restricted stock awards granted to directors in lieu of cash for retainers and meeting fees. Stock elections by directors in lieu of cash for retainer and meeting fees are now fully vested and are expensed at fair value on the date of grant. The modification to 13,863 outstanding restricted stock awards granted to directors resulted in forfeiture of those awards and the granting of new awards which were fully vested and expensed at $37.81 per share, the fair value on the date of grant. Effective fiscal year ended December 31, 2015, other stock-based awards are not included in the tables below. The expense, deferred tax benefit, and current tax expense recognized related to restricted stock and other stock-based awards in 2016 , 2015 and 2014 is presented below (in thousands): 2016 2015 2014 Expense (a) $ 2,594 $ 2,755 $ 3,471 Deferred tax benefit 908 964 1,215 Current tax benefit recognized 183 43 39 _____________________ (a) Any capitalized costs related to these expenses is less than $0.3 million for all years. The aggregate intrinsic value and fair value at grant date of restricted stock and other stock-based awards which vested in 2016 , 2015 and 2014 is presented below (in thousands): 2016 2015 2014 Aggregated intrinsic value $ 2,515 $ 3,451 $ 3,441 Fair value at grant date 1,993 3,327 3,330 The unvested restricted stock transactions for 2016 are presented below: Total Shares Weighted Average Grant Date Fair Value Unrecognized Compensation Expense (a) Aggregate Intrinsic Value (In thousands) (In thousands) Restricted shares outstanding at December 31, 2015 91,210 $ 36.61 Stock awards 74,181 40.95 Vested (55,503 ) 35.91 Forfeitures (495 ) 36.88 Restricted shares outstanding at December 31, 2016 109,393 39.90 $ 1,767 $ 5,087 _______________________ (a) The unrecognized compensation expense is expected to be recognized over the weighted average remaining contractual term of the outstanding restricted stock of approximately one year. The weighted average fair value per share at grant date for restricted stock and other stock-base awards granted during 2016 , 2015 and 2014 were: 2016 2015 2014 Weighted average fair value per share $ 40.95 $ 37.17 $ 36.95 The holder of a restricted stock award has rights as a shareholder of the Company, including the right to vote and receive cash dividends on restricted stock. Restricted Stock with a Market Condition (Performance Shares) . The Company has granted performance share awards to certain officers under the Company’s Amended and Restated 2007 LTIP, which provides for issuance of Company stock based on the achievement of certain performance criteria over a three -year period. The payout varies between 0% to 200% of performance share awards. Detail of performance shares vested follows: Date Vested Payout Ratio Performance Shares Awarded Compensation Costs Expensed Period Compensation Costs Expensed Aggregated Intrinsic Value (In thousands) (In thousands) January 25, 2017 32 % 11,314 $ 932 2014-2016 $ 512 January 27, 2016 0 % 0 851 2013-2015 — February 20, 2015 0 % 0 1,502 2012-2014 — February 18, 2014 0 % 0 954 2011-2013 — In 2017, 2018 and 2019, subject to meeting certain performance criteria, additional performance shares could be awarded. In accordance with the FASB guidance related to stock-based compensation, the Company recognizes the related compensation expense by ratably amortizing the grant date fair value of awards over the requisite service period and the compensation expense is only adjusted for forfeitures. Excluding the 2014 award, the maximum number of shares that can be issued under the plan are 206,898 shares. The fair value at the date of each separate grant of performance shares was based upon a Monte Carlo simulation . The Monte Carlo simulation reflected the structure of the performance plan which calculates the share payout on performance of the Company relative to a defined peer group over a three -year performance period based upon total return to shareholders. The fair value was determined as the average payout of one million simulation paths discounted to the grant date using a risk-free interest rate based upon the constant maturity treasury rate yield curve at the grant date. The expected volatility of total return to shareholders is calculated in accordance with the plan’s term structure and includes the volatilities of all members of the defined peer group. The outstanding performance share awards at the 100% performance level is summarized below: Number Outstanding Weighted Average Grant Date Fair Value Unrecognized Compensation Expense (b) Aggregate Intrinsic Value (In thousands) (In thousands) Performance shares outstanding at December 31, 2015 (a) 130,136 $ 32.72 Performance share awards 60,835 38.11 Performance shares expired (24,527 ) 34.69 Performance shares outstanding at December 31, 2016 (a) 166,444 34.40 $ 2,189 $ 7,740 _______________________ (a) On December 15, 2015, the Company issued a stock based retention grant to the Chief Executive Officer (CEO) of 27,624 shares in accordance with the Amended and Restated 2007 LTIP that is eligible for vesting based on the achievement of certain performance conditions and a five year service period, as stated in the CEO's employment agreement. The performance condition was met as of November 2016 as determined by the Compensation Committee, and has been included in the beginning and ending balance in the table above. (b) The unrecognized compensation expense is expected to be recognized over the weighted average remaining contractual term of the awards of approximately one year, except for the CEO retention grant. A summary of information related to performance shares for 2016 , 2015 and 2014 is presented below: 2016 2015 2014 Weighted average per share grant date fair value per share of performance shares awarded $ 38.11 $ 35.72 $ 26.36 Compensation expense (in thousands) (a) (b) 1,655 1,042 1,181 Deferred tax benefit related to compensation expense (in thousands) (b) 579 365 413 _____________________ (a) Includes adjustments for estimated forfeitures. (b) Includes CEO retention grant. Repurchase Program No shares of the Company's common stock were repurchased during the twelve months ended December 31, 2016 . Detail regarding the Company's stock repurchase program are presented below: Since 1999 Authorized Shares repurchased (b) 25,406,184 Cost, including commission (in thousands) $ 423,647 Total remaining shares available for repurchase at December 31, 2016 393,816 ______________________ (a) Represents repurchased shares and cost since inception of the stock repurchase program in 1999. (b) Shares repurchased does not include 86,735 treasury shares related to employee compensation arrangements outside of the Company's repurchase programs. Beginning in 2015, shares of the Company's common stock issued for employee benefit and stock incentive plans have been issued from the shares repurchased and held in treasury stock. The Company awarded 188,005 shares out of treasury stock during 2016. The Company may in the future make purchases of shares of its common stock pursuant to its authorized program in open market transactions at prevailing prices and may engage in private transactions where appropriate. The repurchased shares will be available for issuance under employee benefit and stock incentive plans, or may be retired. Dividend Policy On December 30, 2016, the Company paid $12.6 million in quarterly cash dividends to shareholders. The Company paid a total of $49.6 million , $47.1 million and $44.6 million in cash dividends during the twelve months ended December 31, 2016 , 2015 and 2014 , respectively. On January 26, 2017 , the Board of Directors declared a quarterly cash dividend of $0.31 per share payable on March 31, 2017 to shareholders of record as of the close of business on March 17, 2017 . Basic and Diluted Earnings Per Share The FASB guidance requires the Company to include share-based compensation awards that qualify as participating securities in both basic and diluted earnings per share to the extent they are dilutive. A share-based compensation award is considered a participating security if it receives non-forfeitable dividends or may participate in undistributed earnings with common stock. The Company awards unvested restricted stock which qualifies as a participating security. The basic and diluted earnings per share are presented below: Years Ended December 31, 2016 2015 2014 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,350,688 40,274,986 40,190,991 Dilutive effect of unvested performance awards 57,345 33,576 20,726 Diluted number of common shares outstanding 40,408,033 40,308,562 40,211,717 Basic net income per common share: Net income $ 96,768 $ 81,918 $ 91,428 Income allocated to participating restricted stock (321 ) (243 ) (301 ) Net income available to common shareholders $ 96,447 $ 81,675 $ 91,127 Diluted net income per common share: Net income $ 96,768 $ 81,918 $ 91,428 Income reallocated to participating restricted stock (321 ) (243 ) (301 ) Net income available to common shareholders $ 96,447 $ 81,675 $ 91,127 Basic net income per common share: Distributed earnings $ 1.225 $ 1.165 $ 1.105 Undistributed earnings 1.165 0.865 1.165 Basic net income per common share $ 2.390 $ 2.030 $ 2.270 Diluted net income per common share: Distributed earnings $ 1.225 $ 1.165 $ 1.105 Undistributed earnings 1.165 0.865 1.165 Diluted net income per common share $ 2.390 $ 2.030 $ 2.270 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: Year Ended December 31, 2016 2015 2014 Restricted stock awards 53,703 56,375 60,455 Performance shares (a) 47,246 66,804 96,208 _____________________ (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.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Notes)	12 Months Ended
	Dec. 31, 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): 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 December 31, 2013 $ (21,330 ) $ 36,240 $ (12,298 ) $ 2,612 Other comprehensive income (loss) before reclassifications (12,628 ) 8,694 — (3,934 ) Amounts reclassified from accumulated other comprehensive income (loss) (926 ) (5,977 ) 224 (6,679 ) Balance at December 31, 2014 (34,884 ) 38,957 (12,074 ) (8,001 ) Other comprehensive income (loss) before reclassifications 3,777 (2,255 ) — 1,522 Amounts reclassified from accumulated other comprehensive income (loss) 1,238 (8,937 ) 264 (7,435 ) Balance at December 31, 2015 (29,869 ) 27,765 (11,810 ) (13,914 ) Other comprehensive income before reclassifications 7,363 6,904 — 14,267 Amounts reclassified from accumulated other comprehensive income (loss) (1,422 ) (6,206 ) 159 (7,469 ) Balance at December 31, 2016 $ (23,928 ) $ 28,463 $ (11,651 ) $ (7,116 ) Amounts reclassified from Accumulated Other Comprehensive Income (Loss) for the twelve months ended December 31, 2016 , 2015 and 2014 are as follows (in thousands): Details about Accumulated Other Comprehensive Income (Loss) Components 2016 2015 2014 Affected Line Item in the Statements of Operations Amortization of pension and post-retirement benefit costs: Prior service benefit $ 7,407 $ 6,574 $ 7,659 (a) Net loss (4,965 ) (8,622 ) (6,182 ) (a) 2,442 (2,048 ) 1,477 (a) Income tax effect (1,020 ) 810 (551 ) Income tax expense 1,422 (1,238 ) 926 Net income Marketable securities: Net realized gain on sale of securities 7,640 11,114 7,350 Investment and interest income, net 7,640 11,114 7,350 Income before income taxes Income tax effect (1,434 ) (2,177 ) (1,373 ) Income tax expense 6,206 8,937 5,977 Net income Loss on cash flow hedge: Amortization of loss (498 ) (467 ) (438 ) Interest on long-term debt and revolving credit facility (498 ) (467 ) (438 ) Income before income taxes Income tax effect 339 203 214 Income tax expense (159 ) (264 ) (224 ) Net income Total reclassifications $ 7,469 $ 7,435 $ 6,679 (a) These items are included in the computation of net periodic benefit cost. See Part II, Item 8, Financial Statements and Supplementary Data, Note M for additional information.

Long-Term Debt and Financing Ob

Long-Term Debt and Financing Obligations (Notes)	12 Months Ended
	Dec. 31, 2016
Long-Term Debt and Financing Obligations [Abstract]
Long-term Debt	Long-Term Debt and Financing Obligations Outstanding long-term debt and financing obligations are as follows: December 31, 2016 2015 (1) (In thousands) Long-Term Debt: Pollution Control Bonds (2): 7.25% 2009 Series A refunding bonds, due 2040 (7.46% effective interest rate) $ 62,619 $ 62,582 4.50% 2012 Series A refunding bonds, due 2042 (4.63% effective interest rate) 58,471 58,441 7.25% 2009 Series B refunding bonds, due 2040 (7.49% effective interest rate) 36,492 36,465 1.875% 2012 Series A refunding bonds, due 2032 (2.35% effective interest rate) 33,193 33,011 Total Pollution Control Bonds 190,775 190,499 Senior Notes (3): 6.00% Senior Notes, net of discount, due 2035 (7.12% effective interest rate) 393,861 393,693 7.50% Senior Notes, net of discount, due 2038 (7.67% effective interest rate) 147,331 147,282 3.30% Senior Notes, net of discount, due 2022 (3.43% effective interest rate) 148,939 148,783 5.00% Senior Notes, net of discount, due 2044 (4.93% effective interest rate) 302,955 147,717 Total Senior Notes 993,086 837,475 RGRT Senior Notes (4): 4.47% Senior Notes, Series B, due 2017 (4.62% effective interest rate) 49,950 49,883 5.04% Senior Notes, Series C, due 2020 (5.16% effective interest rate) 44,845 44,803 Total RGRT Senior Notes 94,795 94,686 Total long-term debt 1,278,656 1,122,660 Financing Obligations: Revolving Credit Facility ($81,574 due in 2017) (5) 81,574 141,738 Total long-term debt and financing obligations 1,360,230 1,264,398 Current Portion (amount due within one year): Current maturities of long term debt (83,143 ) — Short-term borrowings under the revolving credit facility (81,574 ) (141,738 ) $ 1,195,513 $ 1,122,660 _____________________ (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) Pollution Control Bonds ("PCBs") The Company has four series of tax exempt unsecured PCBs in aggregate principal amount of $193.1 million . The 1.875% 2012 Series A (El Paso Electric Company Four Corners Project) Pollution Control Refunding Revenue Bonds with an aggregate principal amount of $33.3 million are subject to mandatory tender for purchase in September 2017 at which time the Company will either repay or remarket these bonds. (3) Senior Notes The Senior Notes are unsecured obligations of the Company. They were issued pursuant to bond covenants that provide limitations on the Company’s ability to enter into certain transactions. The 6.00% Senior Notes have an aggregate principal amount of $400.0 million and were issued in May 2005 . The proceeds, net of a $2.3 million discount, were used to fund the retirement of the Company's first mortgage bonds. The Company amortizes the loss associated with a cash flow hedge recorded in accumulated other comprehensive income to earnings as interest expense over the life of the 6.00% Senior Notes. See Part II, Item 8, Financial Statements and Supplementary Data, Note O. This amortization is included in the effective interest rate of the 6.00% Senior Notes. The 7.50% Senior Notes have an aggregate principal amount of $150.0 million and were issued in June 2008 . The proceeds, net of a $1.3 million discount, were used to repay short-term borrowings of $44.0 million , fund capital expenditures and for other general corporate purposes. The 3.30% Senior Notes have an aggregate principal amount of $150.0 million were issued in December 2012 . The proceeds, net of a $0.3 million discount, were used to fund construction expenditures and for working capital and general corporate purposes. In December 2014 , the Company issued 5.00% Senior Notes with an aggregate principal amount of $150.0 million . The proceeds, net of a $0.5 million discount, were used to fund construction expenditures and for working capital and general corporate purposes. In March 2016 , the Company issued additional 5.00% Senior Notes with an aggregate principal amount of $150.0 million . The proceeds from this issuance, after deducting the underwriters' commission, were $158.1 million . These proceeds included accrued interest of $2.4 million and a $7.1 million premium before expenses. The net proceeds, from the sale of these senior notes were used to repay outstanding short-term borrowings under the RCF. After the March 2016 issuance, the Company's 5.00% Senior Notes due 2044 had a total principal amount outstanding of $300.0 million . (4) RGRT Senior Notes In 2010, the Company and RGRT, a Texas grantor trust through which the Company finances its portion of fuel for Palo Verde, entered into a note purchase agreement with various institutional purchasers. Under the terms of the agreement, RGRT sold to the purchasers $110 million aggregate principal amount of Senior Notes (the "Notes"). In August 2015 , $15.0 million of these Notes matured and were paid with borrowings from the RCF. In August 2017 , $50.0 million of these Senior Notes will mature. The Company will either repay or refinance this $50.0 million of Notes upon maturity. The Company guarantees the payment of principal and interest on the Notes. In the Company’s financial statements, the assets and liabilities of RGRT are reported as assets and liabilities of the Company. RGRT pays interest on the Notes on February 15, and August 15 of each year until maturity. RGRT may redeem the Notes, in whole or in part, at any time at a redemption price equal to 100% of the principal amount to be redeemed together with the interest on such principal amount accrued to the date of redemption, plus a make-whole amount based on the prevailing market interest rates. The agreement requires compliance with certain covenants, including a total debt to capitalization ratio. The Company was in compliance with these requirements throughout 2016. The sale of the Notes was made by RGRT in reliance on a private placement exemption from registration under the Securities Act of 1933, as amended. The proceeds of $109.4 million , net of issuance costs, from the sale of the Notes was used by RGRT to repay amounts borrowed under the RCF and will enable future nuclear fuel financing requirements of RGRT to be met with a combination of the Notes and amounts borrowed from the RCF. (5) Revolving Credit Facility On January 14, 2014, the Company and RGRT entered into a second amended and restated credit agreement related to the RCF with JP Morgan Chase Bank, N.A., as administrative agent and issuing bank, and Union Bank, N.A., as syndication agent, and various lending banks party thereto. As of December 31, 2016, the Company had available $300 million and the ability to increase the RCF by up to $100 million with a term ending January 2019 . On January 9, 2017, the Company exercised its option to extend the maturity of the RCF by one year to January 14, 2020 and to increase the size of the facility by $50 million to $350 million . The Company still has the option to extend the facility by one additional year to January 2021 and to increase the RCF by up to $50 million (up to a total of $400 million ) upon the satisfaction of certain conditions, more fully set forth in the agreement, including obtaining commitments from lenders or third party financial institutions. The RCF provides that amounts borrowed by the Company may be used for, among other things, working capital and general corporate purposes. Any amounts borrowed by RGRT may be used, among other things, to finance the acquisition and processing of nuclear fuel. Amounts borrowed by RGRT are guaranteed by the Company and the balance borrowed under the RCF is recorded as short-term borrowings on the balance sheet. The RCF is unsecured. The RCF requires compliance with certain covenants, including a total debt to capitalization ratio. The Company was in compliance with these requirements throughout 2016. In August 2015 , $15.0 million aggregate principal amount of Series A 3.67% Senior Notes of RGRT matured and were paid utilizing borrowings under the RCF. As of December 31, 2016 , the total amount borrowed by RGRT was $37.6 million for nuclear fuel under the RCF. As of December 31, 2016 , $44.0 million of borrowings were outstanding under this facility for working capital and general corporate purposes. The weighted average interest rate on the RCF was 2.0% as of December 31, 2016 . As of December 31, 2016 , the principal amount of scheduled maturities for the next five years of long-term debt are as follows (in thousands): 2017 $ 83,300 2018 — 2019 — 2020 45,000 2021 — The $37.6 million of borrowings outstanding on the RCF for nuclear fuel financing purposes is anticipated to be paid in 2017.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Taxes [Abstract]
Income Tax Disclosure	Income Taxes The tax effects of temporary differences that give rise to significant portions of the deferred tax assets and liabilities at December 31, 2016 and 2015 are presented below (in thousands): December 31, 2016 2015 Deferred tax assets: Benefit of tax loss carryforwards $ 60,749 $ 35,153 Alternative minimum tax credit carryforward 16,620 16,620 Pensions and benefits 57,756 61,673 Asset retirement obligation 26,929 28,042 Deferred fuel — 1,488 Other (200 ) 15,421 Total gross deferred tax assets 161,854 158,397 Deferred tax liabilities: Plant, principally due to depreciation and basis differences (668,303 ) (608,738 ) Decommissioning (43,463 ) (41,100 ) Deferred fuel (3,962 ) — Other (1,192 ) (3,796 ) Total gross deferred tax liabilities (716,920 ) (653,634 ) Net accumulated deferred income taxes $ (555,066 ) $ (495,237 ) Based on the average annual book income before taxes for the prior three years , excluding the effects of unusual or infrequent items, the Company believes that the deferred tax assets will be fully realized at current levels of book and taxable income. The Company recognized income tax expense for 2016 , 2015 and 2014 as follows (in thousands): Years Ended December 31, 2016 2015 2014 Income tax expense: Federal: Current $ 2,642 $ 2,319 $ (1,250 ) Deferred 47,909 32,819 38,810 Total federal income tax 50,551 35,138 37,560 State: Current 766 1,730 3,209 Deferred 3,285 (1,650 ) 641 Total state income tax 4,051 80 3,850 Generation (amortization) of accumulated investment tax credits (684 ) (323 ) (322 ) Total income tax expense $ 53,918 $ 34,895 $ 41,088 As of December 31, 2016 , the Company had $16.6 million of AMT credit carryforwards that have an unlimited life. As of December 31, 2016 , the Company had $59.3 million of federal and $2.2 million of state tax loss carryforwards. If unused, both the federal and state tax loss carryforwards have lives of 20 years and 5 years respectively. As of December 31, 2016 , the Company had $0.2 million of unrecognized tax benefits related to stock compensation which cannot be recognized until federal tax loss carryforwards are fully utilized. Income tax provisions differ from amounts computed by applying the statutory federal income tax rate of 35% to book income before federal income tax as follows (in thousands): Years Ended December 31, 2016 2015 2014 Federal income tax expense computed on income at statutory rate $ 52,740 $ 40,885 $ 46,381 Difference due to: State taxes, net of federal benefit 2,633 52 1,902 AEFUDC (475 ) (2,345 ) (3,757 ) Permanent tax differences (2,369 ) (2,898 ) (2,921 ) Other 1,389 (799 ) (517 ) Total income tax expense $ 53,918 $ 34,895 $ 41,088 Effective income tax rate 35.8 % 29.9 % 31.0 % The Company files income tax returns in the United States 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 2012. 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. 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 final orders from the PUCT and the NMPRC in its 2015 rate cases, effective January 1, 2016. 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 income tax expense of $5.1 million for the year ended December 31, 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. The 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 decrease of $0.4 million (net of an increase of $0.5 million ), an unrecognized tax position of $0.8 million , and $2.1 million , in 2016 , 2015 , and 2014 respectively, related to transmission and distribution costs and other amounts deducted in current and prior year Texas franchise tax returns. The Company recorded a decrease of $0.3 million in 2016 and a decrease of $1.3 million (net of an increase of $0.4 million ) in 2014 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 December 31, 2016 , 2015 and 2014 amounts of unrecognized tax benefits are as follows (in thousands): 2016 2015 2014 Balance at January 1 $ 6,000 $ 5,200 $ 7,200 Additions for tax positions related to the current year 400 500 300 Reductions for tax positions related to the current year — — — Additions for tax positions of prior years 100 300 2,200 Reductions for tax positions of prior years (1,200 ) — (4,500 ) Balance at December 31 $ 5,300 $ 6,000 $ 5,200 If recognized, $2.6 million of the unrecognized tax position at December 31, 2016 , would reduce the effective tax rate. The Company recognized an income tax benefit for the decrease in unrecognized tax positions of $0.7 million for the year ended December 31, 2016 . The Company recognizes in tax expense interest and penalties related to tax benefits that have not been recognized. For the years ended December 31, 2016 , 2015 , and 2014 the Company recognized interest expense of $0.1 million , $0.2 million , and $0.1 million , respectively. The Company had approximately $0.8 million and $0.7 million accrued for the payment of interest and penalties at December 31, 2016 and 2015 , respectively.

Commitments, Contingencies and

Commitments, Contingencies and Uncertainties	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments, Contingencies And Uncertainties	Commitments, Contingencies and Uncertainties 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 that 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. The Company has entered into the following significant agreements with various counterparties for the purchase and sale of electricity: Commercial Operation Type of Contract Counterparty Quantity Term Date Power Purchase and Sale Agreement Freeport 25 MW December 2008 through December 2018 N/A Power Purchase and Sale Agreement Freeport 100 MW June 2006 through December 2021 N/A Power Purchase Agreement Hatch Solar Energy Center I, LLC 5 MW July 2011 through June 2036 July 2011 Power Purchase Agreement NRG 20 MW August 2011 through August 2031 August 2011 Power Purchase Agreement SunE EPE1, LLC 10 MW June 2012 through June 2037 June 2012 Power Purchase Agreement SunE EPE2, LLC 12 MW May 2012 through May 2037 May 2012 Power Purchase Agreement Macho Springs Solar, LLC 50 MW May 2014 through April 2034 May 2014 Power Purchase Agreement Newman Solar LLC 10 MW December 2014 through November 2044 December 2014 The Company has a firm Power Purchase and Sale Agreement with Freeport-McMoran Copper & Gold Energy Services LLC ("Freeport") that provides for Freeport to deliver energy to the Company from the Luna Energy Facility (a natural gas-fired combined cycle generation facility located in Luna County, New Mexico) and for the Company to deliver a like amount of energy at Greenlee, Arizona. The Company may purchase the quantities noted in the table above at a specified price at times when energy is not exchanged under the Power Purchase and Sale Agreement. The agreement was approved by the FERC and will continue through an initial term ending December 31, 2021, with subsequent rollovers until terminated. Upon mutual agreement, the Power Purchase and Sale Agreement allows the parties to increase the amount of energy that is purchased and sold under the agreement. The parties have agreed to increase the amount up to 125 MW through December 2018. The Company has entered into several power purchase agreements to help meet its renewable portfolio requirements. Namely, the Company has a 25 -year purchase power agreement with Hatch Solar Energy Center I, LLC to purchase all of the output from a solar photovoltaic plant located in southern New Mexico which began commercial operation in July 2011 . In June 2015, the Company entered into a consent agreement with Hatch Solar Energy Center 1, LLC to provide for additional or replacement photovoltaic modules. The Company also entered into a 20 -year contract with NRG Solar Roadrunner LLC ("NRG") to purchase all of the output of a solar photovoltaic plant built in southern New Mexico which began commercial operation in August 2011 . In addition, the Company has 25 -year purchase power agreements to purchase all of the output of two additional solar photovoltaic plants located in southern New Mexico, SunE EPE1, LLC and SunE EPE2, LLC which began commercial operation in June 2012 and May 2012 , respectively. Furthermore, the Company has a 20 -year purchase power agreement with Macho Springs Solar, LLC to purchase the entire generation output delivered from the 50 MW Macho Springs solar photovoltaic plant located in Luna County, New Mexico which began commercial operation in May 2014 . Finally, the Company has a 30 -year purchase power agreement with Newman Solar LLC to purchase the total output of approximately 10 MW from a solar photovoltaic plant on land subleased from the Company in proximity to its Newman Power Station ("Newman"). This solar photovoltaic plant began commercial operation in December 2014 . Environmental Matters General. The Company is subject to extensive laws, regulations and permit requirements with respect to air and greenhouse gas ("GHG") emissions, water discharges, soil and water quality, waste management and disposal, natural resources and other environmental matters by federal, state, regional, tribal and local authorities. Failure to comply with such laws, regulations and requirements can result in actions by authorities or other third parties that might seek to impose on the Company administrative, civil and/or criminal penalties or other sanctions. In addition, releases of pollutants or contaminants into the environment can result in costly cleanup liabilities. These laws, regulations and requirements are subject to change through modification or reinterpretation, or the introduction of new laws and regulations and, as a result, the Company may face additional capital and operating costs to comply. Environmental Litigation and Investigations . Since July 2011, the U.S. Department of Justice (the "DOJ"), on behalf of the EPA, and APS have been engaged in substantive settlement negotiations in an effort to resolve certain of the pending matters. The allegations being addressed through settlement negotiations are that APS failed to obtain the necessary permits and install the controls necessary under the CAA to reduce sulfur dioxide ("SO2"), nitrogen oxides ("NOx"), and particulate matter ("PM"), and that defendants failed to obtain an operating permit under Title V of the CAA that reflects applicable requirements imposed by law. On June 24, 2015, the parties filed with the U.S. District Court for New Mexico a settlement agreement ("CAA Settlement Agreement") resolving this matter. On August 17, 2015, the U.S. District Court for New Mexico entered the CAA Settlement Agreement. The agreement imposes a total civil penalty payable by the co-owners of Four Corners collectively in the amount of $1.5 million , and it requires the co-owners to pay $6.7 million for environmental mitigation projects. At December 31, 2016, the Company has accrued its remaining unpaid share of approximately $0.2 million related to this matter. New Mexico Tax Matter Related to Coal Supplied to Four Corners On May 23, 2013, the New Mexico Taxation and Revenue Department ("NMTRD") issued a notice of assessment for coal severance surtax, penalty, and interest totaling approximately $30.0 million related to coal supplied under the coal supply agreement for Four Corners (the "Assessment"). The Company's share of the Assessment is approximately $1.5 million . On behalf of the Four Corners participants, the coal supplier made a partial payment of the Assessment and immediately filed a refund claim with respect to that partial payment in August 2013. The NMTRD denied the refund claim. On December 19, 2013, the coal supplier and APS, on its own behalf and as operating agent for Four Corners, filed complaints with the New Mexico District Court contesting both the validity of the Assessment and the refund claim denial. On June 30, 2015, the court ruled that the Assessment was not valid and further ruled that APS and the other Four Corners co-owners receive a refund of all of the contested amounts previously paid under the applicable tax statute. The NMTRD filed a Notice of Appeal on August 31, 2015 with respect to the decision. Thereafter, APS and the coal supplier entered into a final settlement agreement with the NMTRD with respect to the Assessment. Pursuant to the final settlement agreement, the NMTRD agreed to release the Assessment, dismiss its filed appeal, and release its rights to any other surtax claims with respect to the coal supply agreement. APS and the other Four Corners participants agreed to forgo refund rights with respect to all the contested amounts previously paid under the applicable tax statute, in addition to a $1.0 million settlement payment. The Company paid its share of this settlement, approximately $47,000 , in April 2016. Lease Agreements The Company leases land in El Paso, Texas, adjacent to Newman under a lease which expires in June 2033 with a renewal option of 25 years . The Company also has several other leases for office, parking facilities and equipment which expire within the next 4 years . The Company has transmission and distribution lines which are operated under various property easement agreements. The majority of these easements include renewal options which the Company routinely exercises. These lease agreements do not impose any restrictions relating to issuance of additional debt, payment of dividends or entering into other lease arrangements. The Company has no significant capital lease agreements. The Company's total annual rental expense related to operating leases was $1.7 million , $1.9 million , and $1.8 million for 2016 , 2015 and 2014 , respectively. As of December 31, 2016 , the Company’s minimum future rental payments for the next five years are as follows (in thousands): 2017 $ 808 2018 662 2019 666 2020 664 2021 562 Union Matters The Company has approximately 1,100 employees, about 38% of whom are covered by a collective bargaining agreement. The International Brotherhood of Electrical Workers Local 960 ("Local 960") represents the Company’s employees working primarily in the power plants, substations, line crews, meter reading and collection, facilities services, and customer service. The Company entered into a new collective bargaining agreement effective September 3, 2016 , with Local 960 for a three -year term ending September 3, 2019 . The agreement provides for pay increases of 3% on September 3, 2016, September 3, 2017 and on September 3, 2018, respectively.

Litigation

Litigation	12 Months Ended
	Dec. 31, 2016
Litigation [Abstract]
Legal Matters and Contingencies	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 Part II, Item 8, Financial Statements and Supplementary Data, Note C and Note K for discussion of the effects of government legislation and regulation on the Company as well as certain pending legal proceedings.

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Pension and Other Postretirement Benefits Disclosure	Employee Benefits Retirement Plans The Company’s Retirement Income Plan (the "Retirement Plan") is a qualified noncontributory defined benefit plan. Upon retirement or death of a vested plan participant, assets of the Retirement Plan are used to pay benefit obligations under the Retirement Plan. Contributions from the Company are based on various factors such as the minimum funding amounts required by the Internal Revenue Service ("IRS"), state and federal regulatory requirements, amounts collected from customers in the Company's Texas and New Mexico jurisdictions and the annual cost of the Retirement Plan, as actuarially calculated. The assets of the Retirement Plan are primarily invested in common collective trusts which hold equity securities, debt securities and cash equivalents and are managed by a professional investment manager appointed by the Company. The Company has two non-qualified retirement plans that are non-funded defined benefit plans. The Company's Supplemental Retirement Plan covers certain former employees and directors of the Company. The Excess Benefit Plan, was adopted in 2004 and covers certain active and former employees of the Company. The benefit cost for the non-qualified retirement plans are based on substantially the same actuarial methods and economic assumptions as those used for the Retirement Plan. During the quarter ended March 31, 2014 , the Company implemented certain amendments to the Retirement Plan and Excess Benefit Plan. In the first quarter of 2014 , the Company offered a cash balance pension plan as an alternative to its current final average pay pension plan for employees hired prior to January 1, 2014 . The cash balance pension plan also included an enhanced employer matching contribution to the employee’s respective 401(k) Defined Contribution Plan (discussed below). For employees that elected the new cash balance feature of the plans, the pension benefit earned under the existing final average pay feature of the plans was frozen as of March 31, 2014 . Employees hired after January 1, 2014 were automatically enrolled in the cash balance pension plan. The amendments to the plans were effective April 1, 2014 . As a result of these actions, the Company remeasured the assets and liabilities of the plans, based on actuarially determined estimates, using the close of the alternative choice election period of February 28, 2014 , as the remeasurement date. Prior to December 31, 2013 , employees who completed one year of service with the Company and worked at least a minimum number of hours each year were covered by the final average pay formula of the plan. For participants that continue to be covered by the final average pay formula, retirement benefits are based on the employee’s final average pay and years of service. The cash balance pension plan covers employees beginning on their employment commencement date or re-employment commencement date in any plan year in which the employee completes at least a minimum number of hours of service. Retirement benefits under the cash balance pension plan are based on the employee’s cash balance account, consisting of pay credits and interest credits. The Company complies with the FASB guidance on disclosure for pension and other post-retirement plans that requires disclosure of investment policies and strategies, categories of investment and fair value measurements of plan assets, and significant concentrations of risk. The obligations and funded status of the plans are presented below (in thousands): December 31, 2016 2015 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Change in projected benefit obligation: Benefit obligation at end of prior year $ 325,706 $ 26,958 $ 341,133 $ 28,397 Service cost 7,705 296 8,530 262 Interest cost 12,161 878 13,477 1,018 Actuarial (gain) loss 7,988 1,267 (19,290 ) (810 ) Benefits paid (15,792 ) (1,937 ) (18,144 ) (1,909 ) Benefit obligation at end of year 337,768 27,462 325,706 26,958 Change in plan assets: Fair value of plan assets at end of prior year 260,035 — 272,939 — Actual return (loss) on plan assets 18,223 — (3,760 ) — Employer contribution 7,300 1,937 9,000 1,909 Benefits paid (15,792 ) (1,937 ) (18,144 ) (1,909 ) Fair value of plan assets at end of year 269,766 — 260,035 — Funded status at end of year $ (68,002 ) $ (27,462 ) $ (65,671 ) $ (26,958 ) Amounts recognized in the Company's balance sheets consist of the following (in thousands): December 31, 2016 2015 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Current liabilities $ — $ (2,696 ) $ — $ (2,102 ) Noncurrent liabilities (68,002 ) (24,766 ) (65,671 ) (24,856 ) Total $ (68,002 ) $ (27,462 ) $ (65,671 ) $ (26,958 ) The accumulated benefit obligation in excess of plan assets is as follows (in thousands): December 31, 2016 2015 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Projected benefit obligation $ (337,768 ) $ (27,462 ) $ (325,706 ) $ (26,958 ) Accumulated benefit obligation (314,071 ) (25,550 ) (302,446 ) (25,785 ) Fair value of plan assets 269,766 — 260,035 — Pre-tax amounts recognized in accumulated other comprehensive income consist of the following (in thousands): Years Ended December 31, 2016 2015 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Net loss $ 121,052 $ 10,073 $ 118,963 $ 9,592 Prior service benefit (23,877 ) (185 ) (27,344 ) (224 ) Total $ 97,175 $ 9,888 $ 91,619 $ 9,368 The following are the weighted-average actuarial assumptions used to determine the benefit obligations: December 31, 2016 2015 Non-Qualified Non-Qualified Retirement Income Plan Supplemental Retirement Plan Excess Benefit Plan Retirement Income Plan Supplemental Retirement Plan Excess Benefit Plan Discount rate 4.29 % 3.76 % 4.34 % 4.57 % 3.99 % 4.59 % Rate of compensation increase 4.5 % N/A 4.5 % 4.5 % N/A 4.5 % The Company reassesses various actuarial assumptions at least on an annual basis. The discount rate is reviewed at each measurement date. The discount rate used to measure the fiscal year end obligation is based on a segmented spot rate yield curve that matches projected future payments with the appropriate interest rate applicable to the timing of the projected future benefit payments. A 1% increase in the discount rate would decrease the December 31, 2016 retirement plans' projected benefit obligation by 11.5% . A 1% decrease in the discount rate would increase the December 31, 2016 retirement plans' projected benefit obligation by 14.1% . The components of net periodic benefit cost are presented below (in thousands): Years Ended December 31, 2016 2015 2014 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Service cost $ 7,705 $ 296 $ 8,530 $ 262 $ 8,284 $ 303 Interest cost 12,161 878 13,477 1,018 14,001 1,041 Expected return on plan assets (18,879 ) — (19,795 ) — (18,699 ) — Amortization of: Net loss 6,554 785 9,710 937 8,178 675 Prior service benefit (3,467 ) (39 ) (3,467 ) (39 ) (2,889 ) (17 ) Net periodic benefit cost $ 4,074 $ 1,920 $ 8,455 $ 2,178 $ 8,875 $ 2,002 In 2016, the Company changed the method used to estimate the service and interest components of net periodic benefit cost for pension benefits . This change, compared to the previous method, resulted in a decrease in the service cost and interest cost components in 2016, and is expected to result in a decrease in the service cost and interest cost components in future periods. Historically, the Company estimated service and interest costs utilizing a single weighted-average discount rate derived from the yield curve used to measure the benefit obligation at the beginning of the period. In 2016, the Company elected to utilize a full yield curve approach to estimate these components by applying the specific spot rates along the yield curve used in the determination of the benefit obligation to the relevant projected cash flows. The Company believes the new approach provides a more precise measurement of service and interest costs by aligning the timing of the plan’s liability cash flows to the corresponding spot rates on the yield curve. The Company accounted for this change as a change in accounting estimate and accordingly, accounted for this prospectively. The change in estimate decreased the service and interest components of net periodic benefit cost in 2016 by approximately $2.9 million . The changes in benefit obligations recognized in other comprehensive income are presented below (in thousands): Years Ended December 31, 2016 2015 2014 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Net (gain) loss $ 8,644 $ 1,266 $ 4,266 $ (811 ) $ 47,324 $ 3,508 Prior service benefit — — — — (33,700 ) (500 ) Amortization of: Net loss (6,554 ) (785 ) (9,710 ) (937 ) (8,178 ) (675 ) Prior service benefit 3,467 39 3,467 39 2,889 17 Total recognized in other comprehensive income $ 5,557 $ 520 $ (1,977 ) $ (1,709 ) $ 8,335 $ 2,350 The total amount recognized in net periodic benefit costs and other comprehensive income are presented below (in thousands): Years Ended December 31, 2016 2015 2014 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Total recognized in net periodic benefit cost and other comprehensive income $ 9,631 $ 2,440 $ 6,478 $ 469 $ 17,210 $ 4,352 The following are amounts in accumulated other comprehensive income that are expected to be recognized as components of net periodic benefit cost during 2017 (in thousands): Retirement Income Plan Non-Qualified Retirement Plans Net loss $ 7,530 $ 825 Prior service benefit (3,470 ) (40 ) The following are the weighted-average actuarial assumptions used to determine the net periodic benefit cost for the twelve months ended December 31 : 2016 2015 2014 (a) Non-Qualified Non-Qualified Non-Qualified Retirement Income Plan Supplemental Retirement Plan Excess Benefit Plan Retirement Income Plan Supplemental Retirement Plan Excess Benefit Plan Retirement Income Plan Supplemental Retirement Plan Excess Benefit Plan Discount rate Benefit obligation 4.57 % 3.99 % 4.63 % 4.0 % 3.4 % 4.1 % 4.9 % 3.9 % 4.9 % Service cost 4.83 % N/A 4.87 % 4.0 % N/A 4.1 % 4.9 % N/A 4.9 % Interest cost 3.86 % 3.04 % 3.9 % 4.0 % 3.4 % 4.1 % 4.9 % 3.9 % 4.9 % Expected long-term return on plan assets 7.0 % N/A N/A 7.5 % N/A N/A 7.5 % N/A N/A Rate of compensation increase 4.5 % N/A 4.5 % 4.5 % N/A 4.5 % 4.75 % N/A 4.75 % _____________________ (a) The Retirement Plan and the Excess Benefit Plan were remeasured on February 28, 2014 due to the above mentioned plan amendment. The discount rate used to remeasure the benefit obligation was 4.6% for the Retirement Plan and 4.5% for the Excess Benefit Plan, compared to 4.9% for both plans as of January 1, 2014 . All other assumptions remained consistent with assumptions used at January 1, 2014 . The Company’s overall expected long-term rate of return on assets is 7.0% effective January 1, 2016 and January 1, 2017, which is both a pre-tax and after-tax rate as pension funds are generally not subject to income tax. The expected long-term rate of return is based on the weighted average of the expected returns on investments based upon the target asset allocation of the pension fund. The Company’s target allocations for the plan’s assets are presented below: December 31, 2016 Equity securities 50 % Fixed income 40 % Alternative investments 10 % Total 100 % The Retirement Plan invests the majority of its plan assets in common collective trusts which includes a diversified portfolio of domestic and international equity securities and fixed income securities. Alternative investments of the Retirement Plan are comprised of a real estate limited partnership and equity securities of real estate companies. The expected rate of returns for the funds are assessed annually and are based on long-term relationships among major asset classes and the level of incremental returns that can be earned by the successful implementation of different active investment management strategies. Equity and real estate equity returns are based on estimates of long-term inflation rate, real rate of return, 10-year Treasury bond premium over cash, an expected equity risk premium, as well as other economic factors. Fixed income returns are based on maturity, long-term inflation, real rate of return and credit spreads. These assumptions also capture the expected correlation of returns between these asset classes over the long term. The FASB guidance on disclosure for pension plans requires disclosure of fair value measurements of plan assets. To increase consistency and comparability in fair value measurements, the FASB guidance on fair value measurements established 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. Prices of securities held in the mutual funds and underlying portfolios of the Retirement Plan are primarily obtained from independent pricing services. These prices are based on observable market data. The Common Collective Trusts 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 concluded that the NAV used for determining the fair value of the investments in the Common Collective Trusts have readily determinable fair values. Accordingly, such fund values have been re-categorized from Level 2 to Level 1 hierarchy. Level 2 – Inputs other than quoted market prices included in Level 1 that are observable for the asset or liability either directly or indirectly. The fair value of these investments are 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. The fair value of the Company’s Retirement Plan assets at December 31, 2016 and 2015 , and the level within the three levels of the fair value hierarchy defined by the FASB guidance on fair value measurements are presented in the table below (in thousands): Description of Securities Fair Value as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and Cash Equivalents $ 932 $ 932 $ — $ — Common Collective Trusts (a) Equity funds 144,081 144,081 — — Fixed income funds 109,356 109,356 — — Real Estate Funds 8,406 8,406 — — Total Common Collective Trusts 261,843 261,843 — — Limited Partnership Interest in Real Estate (b)(c) 6,991 Total Plan Investments $ 269,766 $ 262,775 $ — $ — 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) Cash and Cash Equivalents $ 1,266 $ 1,266 $ — $ — Common Collective Trusts (a) Equity funds 144,279 144,279 — — Fixed income funds 103,877 103,877 — — Real Estate Funds 2,025 2,025 — — Total Common Collective Trusts 250,181 250,181 — — Limited Partnership Interest in Real Estate (b)(c) 8,588 Total Plan Investments $ 260,035 $ 251,447 $ — $ — _____________________ (a) The Common Collective Trusts are invested in equity and fixed income securities, or a combination thereof. The investment objective of each fund is to produce returns in excess of, or commensurate with, its predefined index. (b) This investment is a commercial real estate partnership that purchases land, develops limited infrastructure, and sells it for commercial development. The Company was restricted from selling its partnership interest during the life of the partnership, which spanned 7 years. Return on investment is realized as land is sold. The fair value of the limited partnership interest in real estate is based on the NAV of the partnership which reflects the appraised value of the land. The partnership term expired on June 30, 2016 . Upon expiration, dissolution of the partnership commenced and, as a result, the general partner of the partnership is attempting to sell the remaining inventory as soon as possible at the highest pricing possible. (c) In the first quarter of 2016, the Company implemented ASU 2015-07, Fair Value Measurement (Topic 820) which eliminates the requirement to categorize investments in the fair value hierarchy if the fair value is measured at NAV per share (or its equivalent) using the practical expedient in the FASB’s fair value measurement gui dance . The fair value amounts presented in the table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the statement of financial position. ASU 2015-07 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. The table below reflects the changes in the fair value of investments in the real estate limited partnership during the period (in thousands): Fair Value of Investments in Real Estate Balances at December 31, 2014 $ 8,748 Unrealized loss in fair value (160 ) Balances at December 31, 2015 8,588 Sale of land (775 ) Unrealized loss in fair value (822 ) Balances at December 31, 2016 $ 6,991 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 twelve month periods ending December 31, 2016 and 2015 . There were no purchases, issuances, and settlements related to the assets in the Level 3 fair value measurement category during the twelve month periods ending December 31, 2016 and 2015 . The Company adheres to the traditional capital market pricing theory which maintains that over the long term, the risk of owning equities should be rewarded with a greater return than available from fixed income investments. The Company seeks to minimize the risk of owning equity securities by investing in funds that pursue risk minimization strategies and by diversifying its investments to limit its risks during falling markets. The investment manager has full discretionary authority to direct the investment of plan assets held in trust within the guidelines prescribed by the Company through the plan’s investment policy statement including the ability to hold cash equivalents. The investment guidelines of the investment policy statement are in accordance with the Employee Retirement Income Security Act of 1974 ("ERISA") and Department of Labor ("DOL") regulations. The Company contributes at least the minimum funding amounts required by the IRS for the Retirement Plan, as actuarially calculated. The Company expects to contribute at least $10.0 million to its retirement plans in 2017 . The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid (in thousands): Retirement Income Plan Non-Qualified Retirement Plans 2017 $ 16,113 $ 2,698 2018 19,080 2,060 2019 18,771 2,025 2020 18,923 1,957 2021 19,755 1,907 2022-2026 107,916 8,949 401(k) Defined Contribution Plans The Company sponsors 401(k) defined contribution plans covering substantially all employees. Annual matching contributions made to the savings plans for the years 2016 , 2015 and 2014 were $4.1 million , $3.9 million , and $3.0 million , respectively. Historically, the Company had provided a 50 percent matching contribution up to 6 percent of the employee’s compensation subject to certain other limits and exclusions. Effective April 1, 2014 , for employees who enrolled in the cash balance pension plan (discussed above), the Company provided a 100 percent matching contribution up to 6 percent of the employee's compensation subject to certain other limits and exclusions. Other Post-retirement Benefits The Company provides certain health care benefits for retired employees and their eligible dependents and life insurance benefits for retired employees only. Substantially all of the Company’s employees may become eligible for those benefits if they retire while working for the Company. Contributions from the Company are based on various factors such as the Plan's funded status, the IRS tax deductible limit, state and federal regulatory requirements, amounts collected from customers in the Company's Texas and New Mexico jurisdictions and the annual cost of the Plan, as actuarially calculated. The assets of the plan are primarily invested in institutional funds which hold equity securities, debt securities, and cash equivalents and are managed by a professional investment manager appointed by the Company. The following table contains a reconciliation of the change in the benefit obligation, the fair value of plan assets, and the funded status of the plan (in thousands): December 31, 2016 2015 Change in benefit obligation: Benefit obligation at end of prior year $ 92,643 $ 100,700 Service cost 2,769 3,454 Interest cost 3,167 4,035 Actuarial loss (gain) 10,751 (11,423 ) Amendment (a) (b) (32,697 ) (824 ) Benefits paid (4,428 ) (4,544 ) Retiree contributions 1,310 1,245 Benefit obligation at end of year 73,515 92,643 Change in plan assets: Fair value of plan assets at end of prior year 38,090 41,358 Actual return (loss) on plan assets 2,443 (469 ) Employer contribution 1,700 500 Benefits paid (4,428 ) (4,544 ) Retiree contributions 1,310 1,245 Fair value of plan assets at end of year 39,115 38,090 Funded status at end of year $ (34,400 ) $ (54,553 ) _____________________ (a) During October 2016, the Company approved and communicated a plan amendment that resulted in a remeasurement of the Company's Other Post-retirement Benefit Plan. Effective January 1, 2017, retirees and dependents that are less than 65 years of age are offered a choice between a $1,000 and $2,250 deductible plan. Additionally, retirees and dependents that are 65 years of age or greater were covered by a fully insured Medicare advantage plan. (b) Amendment relates to modification of the Company's Other Post-retirement Benefit Plan which increased mail order co-payments for post age 65. The amendment was approved in 2015 and became effective January 1, 2016 . Amounts recognized in the Company's balance sheets consist of the following (in thousands): December 31, 2016 2015 Current liabilities $ — $ — Noncurrent liabilities (34,400 ) (54,553 ) Total $ (34,400 ) $ (54,553 ) Pre-tax amounts recognized in accumulated other comprehensive income consist of the following (in thousands): December 31, 2016 2015 Net gain $ (26,285 ) $ (38,802 ) Prior service benefit (41,009 ) (12,213 ) Total $ (67,294 ) $ (51,015 ) The following are the weighted-average actuarial assumptions used to determine the accrued post-retirement benefit obligations: December 31, 2016 2015 Discount rate at end of year 4.36 % 4.59 % Health care cost trend rates: Initial Pre-65 medical 6.50 % 7.00 % Post-65 medical 4.50 % 7.00 % Pre-65 drug 7.50 % 7.00 % Post-65 drug 10.50 % 7.00 % Ultimate 4.50 % 4.50 % Year ultimate reached (a) 2026 2026 _____________________ (a) Pre-65 medical reaches the ultimate trend rate in 2025. Additionally, the Post-65 medical trend is assumed to be 4.50% for all years into the future. The discount rate is reviewed at each measurement date. The discount rate used to measure the fiscal year end obligation is based on a segmented spot rate yield curve that matches projected future payments with the appropriate interest rate applicable to the timing of the projected future benefit payments. A 1% increase in the discount rate would decrease the December 31, 2016 accumulated post-retirement benefit obligation by 13.1% . A 1% decrease in the discount rate would increase the December 31, 2016 accumulated post-retirement benefit obligation by 16.7% . Net periodic benefit cost is made up of the components listed below (in thousands): Years Ended December 31, 2016 2015 2014 Service cost $ 2,769 $ 3,454 $ 2,845 Interest cost 3,167 4,035 4,463 Expected return on plan assets (1,835 ) (2,070 ) (2,116 ) Amortization of: Prior service benefit (3,901 ) (3,068 ) (4,753 ) Net gain (2,374 ) (2,025 ) (2,671 ) Net periodic benefit cost $ (2,174 ) $ 326 $ (2,232 ) In 2016, the Company changed the method used to estimate the service and interest components of net periodic benefit cost for other post-retirement benefits . This change, compared to the previous method, resulted in a decrease in the service cost and interest cost components in 2016, and is expected to result in a decrease in the service cost and interest cost components in future periods. Historically, the Company estimated service and interest costs utilizing a single weighted-average discount rate derived from the yield curve used to measure the benefit obligation at the beginning of the period. In 2016, the Company elected to utilize a full yield curve approach to estimate these components by applying the specific spot rates along the yield curve used in the determination of the benefit obligation to the relevant projected cash flows. The Company believes the new approach provides a more precise measurement of service and interest costs by aligning the timing of the plan’s liability cash flows to the corresponding spot rates on the yield curve. The Company accounted for this change as a change in accounting estimate and accordingly, accounted for this prospectively. The change in estimate decreased the service and interest components of net periodic benefit cost in 2016 by approximately $0.8 million . The changes in benefit obligations recognized in other comprehensive income are presented below (in thousands): Years Ended December 31, 2016 2015 2014 Net (gain) loss $ 10,143 $ (8,884 ) $ 3,496 Prior service benefit (32,697 ) (824 ) — Amortization of: Prior service benefit 3,901 3,068 4,753 Net gain 2,374 2,025 2,671 Total recognized in other comprehensive income $ (16,279 ) $ (4,615 ) $ 10,920 The total amount recognized in net periodic benefit cost and other comprehensive income are presented below (in thousands): Years Ended December 31, 2016 2015 2014 Total recognized in net periodic benefit cost and other comprehensive income $ (18,453 ) $ (4,289 ) $ 8,688 The amount in accumulated other comprehensive income that is expected to be recognized as a component of net periodic benefit cost during 2017 is a prior service benefit of $6.2 million and a net gain of $1.6 million . The following are the weighted-average actuarial assumptions used to determine the net periodic benefit cost for the twelve months ended December 31 : 2016 (a) 2015 2014 Discount rate: January 1 - September 30 October 1 - December 31 Benefit obligation 4.59 % 3.75 % 4.1 % 4.9 % Service cost 4.91 % 4.03 % 4.1 % 4.9 % Interest cost 3.86 % 3.15 % 4.1 % 4.9 % Expected long-term return on plan assets 4.875% 5.2 % 5.2 % Health care cost trend rates: Initial 7.00% 7.25 % 7.5 % Ultimate 4.5% 4.5 % 4.5 % Year ultimate reached 2026 2026 2026 _____________________ (a) The actuarial assumptions are evaluated by the Company at each measurement date. The Other Post-retirement Benefits Plan was remeasured at October 1, 2016 due to a plan amendment. For measurement purposes, a 7.0% annual rate of increase in the per capita cost of covered health care benefits was assumed for 2016 . The rate was assumed to decrease gradually to 4.5% for 2026 and remain at that level thereafter. Assumed health care cost trend rates have a significant effect on the amounts reported for the health care plan. The effect of a 1% change in these assumed health care cost trend rates would increase or decrease the December 31, 2016 benefit obligation by $11.2 million or $9.0 million , respectively. In addition, a 1% change in said rate would increase or decrease the aggregate 2016 service and interest cost components of the net periodic benefit cost by $1.3 million or $1.0 million , respectively. The Company’s overall expected long-term rate of return on assets, on an after-tax basis, is 4.875% effective January 1, 2016 and January 1, 2017. The expected long-term rate of return is based on the after-tax weighted average of the expected returns on investments based upon the target asset allocation. The Company’s target allocations for the plan’s assets are presented below: December 31, 2016 Equity securities 65 % Fixed income 30 % Alternative investments 5 % Total 100 % The Other Post-retirement Benefit Plan invests the majority of its plan assets in institutional funds which includes a diversified portfolio of domestic and international equity securities and fixed income securities. The asset portfolio also includes cash equivalents and a real estate limited partnership. The expected rates of return for the funds are assessed annually and are based on long-term relationships among major asset classes and the level of incremental returns that can be earned by the successful implementation of different active investment management strategies. Equity returns are based on estimates of long-term inflation rate, real rate of return, 10-year Treasury bond premium over cash, an expected equity risk premium, as well as other economic factors. Fixed income returns are based on maturity, long-term inflation, real rate of return and credit spreads. These assumptions also capture the expected correlation of returns between these asset classes over the long term. The FASB guidance on disclosure for other post-retirement benefit plans requires disclosure of fair value measurements of plan assets. To increase consistency and comparability in fair value measurements, the FASB guidance on fair value measurements established 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. Prices of securities held in the mutual funds and underlying portfolios of the Other Post-retirement Benefits Plan are primarily obtained from independent pricing services. These prices are based on observable market data. 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 concluded that the NAV used for determining the fair value of the investments in the institutional funds have readily determinable fair values. Accordingly, such fund values have been re-categorized from Level 2 to Level 1 hierarchy. • Level 2 – Inputs other than quoted market prices included in Level 1 that are observable for the asset or liability either directly or indirectly. The fair value of these investments are 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. The fair value of the Company’s Other Post-retirement Benefits Plan assets at December 31, 2016 and 2015 , and the level within the three levels of the fair value hierarchy defined by the FASB guidance on fair value measurements are presented in the table below (in thousands): Description of Securities Fair Value as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Institutional Funds (a) Equity funds $ 26,133 $ 26,133 $ — $ — Fixed income funds 11,671 11,671 — — Total Institutional Funds 37,804 37,804 — — Limited Partnership Interest in Real Estate (b) (c) 1,311 Total Plan Investments $ 39,115 $ 37,804 $ — $ — 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) Institutional Funds (a) Equity funds $ 24,881 $ 24,881 $ — $ — Fixed income funds 11,599 11,599 — — Total Ins

Franchises and Significant Cust

Franchises and Significant Customers	12 Months Ended
	Dec. 31, 2016
Franchises and Significant Customers [Abstract]
Franchises And Significant Customers	Franchises and Significant Customers Franchises The Company operates under franchise agreements with several cities in its service territory, including one with El Paso, Texas, the largest city it serves. The franchise agreement allows the Company to utilize public rights-of-way necessary to serve its customers within El Paso. Pursuant to the El Paso franchise agreement, which was amended in 2010, the Company pays to the City of El Paso, on a quarterly basis, a fee equal to 4.00% of gross revenues the Company receives for the generation, transmission and distribution of electrical energy and other services within the city. The 2005 El Paso franchise agreement set the franchise fee at 3.25% of gross revenues, but the 2010 amendment added an incremental fee equal to 0.75% of gross revenues to be placed in a restricted fund to be used by the city solely for economic development and renewable energy purposes. Any assignment of the franchise agreement, including a deemed assignment as a result of a change in control of the Company, requires the consent of the City of El Paso. The El Paso franchise agreement is set to expire on July 31, 2030 . The Company does not have a written franchise agreement with the City of Las Cruces, the second largest city in its service territory. The Company provides electric distribution service to the City of Las Cruces under an implied franchise by satisfying all obligations under the franchise agreement that expired on April 30, 2009 . The Company pays the City of Las Cruces a franchise fee of 2.00% of gross revenues the Company receives from services within the City of Las Cruces. Military Installations The Company serves HAFB, White Sands Missile Range (" White Sands ") and Fort Bliss. These military installations represent approximately 2.8% of the Company's annual retail revenues. In July 2014, the Company signed an agreement with Fort Bliss under which Fort Bliss takes retail electric service from the Company under the applicable Texas tariffs . The Company serves White Sands under the applicable New Mexico tariffs. In August 2016, the Company signed a contract with HAFB under which the Company provides retail electric service and limited wheeling services to HAFB under the applicable New Mexico tariffs. As stated in the contract, HAFB will purchase the full output of a Company-owned 5 MW solar facility upon its completed construction, with HAFB's other power requirements provided under the applicable New Mexico tariffs.

Financial Instruments and Inves

Financial Instruments and Investments (Notes)	12 Months Ended
	Dec. 31, 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 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): December 31, 2016 2015 Carrying Amount (1) Estimated Fair Value Carrying Amount (1) Estimated Fair Value Pollution Control Bonds $ 190,775 $ 206,818 $ 190,499 $ 212,624 Senior Notes 993,086 1,112,285 837,475 829,864 RGRT Senior Notes (2) 94,795 98,855 94,686 100,345 RCF (2) 81,574 81,574 141,738 141,738 Total $ 1,360,230 $ 1,499,532 $ 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 December 31, 2016 and December 31, 2015 , is funded through the $95 million RGRT Senior Notes and $37.6 million and $33.7 million , respectively under the RCF. As of December 31, 2016 , $44.0 million was outstanding under the RCF for working capital or general corporate purposes. As of December 31, 2015 , $108.0 million amount 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 period reflecting current market rates. Consequently, the carrying value approximates fair value. Treasury Rate Locks. The Company entered into treasury rate lock agreements in 2005 to hedge against potential movements in the treasury reference interest rate pending the issuance of the 6% Senior Notes. The treasury rate lock agreements met the criteria for hedge accounting and were designated as a cash flow hedge. In accordance with cash flow hedge accounting, the Company recorded the loss associated with the fair value of the cash flow hedge, net of tax, as a component of accumulated other comprehensive loss and amortizes the accumulated comprehensive loss to earnings as interest expense over the life of the 6% Senior Notes. In 2017, approximately $0.5 million of this accumulated other comprehensive loss item will be reclassified to interest expense. Contracts and Derivative Accounting. The Company uses commodity contracts to manage its exposure to price and availability risks for fuel purchases and power sales and purchases and these contracts generally have the characteristics of derivatives. The Company does not trade or use these instruments with the objective of earning financial gains on the commodity price fluctuations. The Company has determined that all such contracts outstanding at December 31, 2016 , except for certain natural gas commodity contracts with optionality features, that had the characteristics of derivatives met the "normal purchases and normal sales" exception provided in the FASB guidance for accounting for derivative instruments and hedging activities, and, as such, were not required to be accounted for as derivatives. Marketable Securities. The Company’s marketable securities, included in decommissioning trust funds in the balance sheets, are reported at fair value which was $255.7 million and $239.0 million at December 31, 2016 and 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): December 31, 2016 Less than 12 Months 12 Months or Longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Description of Securities (1) : Federal Agency Mortgage Backed Securities $ 11,582 $ (239 ) $ 436 $ (22 ) $ 12,018 $ (261 ) U.S. Government Bonds 31,655 (762 ) 17,976 (835 ) 49,631 (1,597 ) Municipal Obligations 9,596 (394 ) 4,067 (372 ) 13,663 (766 ) Corporate Obligations 7,971 (172 ) 2,092 (172 ) 10,063 (344 ) Total Debt Securities 60,804 (1,567 ) 24,571 (1,401 ) 85,375 (2,968 ) Common Stock 2,760 (167 ) — — 2,760 (167 ) Institutional Funds-International Equity 22,945 (110 ) — — 22,945 (110 ) Total Temporarily Impaired Securities $ 86,509 $ (1,844 ) $ 24,571 $ (1,401 ) $ 111,080 $ (3,245 ) ____________________ (1) Includes approximately 152 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 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 approximately 133 securities. The Company monitors the length of time specific securities trade below its 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 twelve months ended December 31, 2016 , 2015 , and 2014 , the Company recognized other than temporary impairment losses on its available-for-sale securities as follows (in thousands): 2016 2015 2014 Unrealized holding losses included in pre-tax income $ (352 ) $ (338 ) $ — 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): December 31, 2016 December 31, 2015 Fair Value Unrealized Gains Fair Value Unrealized Gains Description of Securities: Federal Agency Mortgage Backed Securities $ 7,430 $ 319 $ 9,589 $ 438 U.S. Government Bonds 12,237 138 12,033 136 Municipal Obligations 2,481 144 8,671 332 Corporate Obligations 12,350 655 10,110 368 Total Debt Securities 34,498 1,256 40,403 1,274 Common Stock 61,884 34,066 72,636 37,001 Equity Mutual Funds 42,244 3,345 18,853 91 Cash and Cash Equivalents 6,002 — 8,204 — Total $ 144,628 $ 38,667 $ 140,096 $ 38,366 The Company’s marketable securities include investments in mortgage backed securities, municipal, corporate and federal debt obligations. The contractual year for maturity for these available-for-sale securities as of December 31, 2016 is as follows (in thousands): Total 2017 2018 through 2022 through 2026 2027 and Beyond Municipal Debt Obligations $ 16,144 $ 990 $ 6,253 $ 8,139 $ 762 Corporate Debt Obligations 22,413 — 8,664 6,090 7,659 U.S. Government Bonds 61,868 14,272 22,495 14,786 10,315 Federal Agency Mortgage Backed Securities 19,448 — 5 390 19,053 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 out of accumulated other comprehensive income and into net income. The proceeds from the sale of these securities during the twelve months ended December 31, 2016 , 2015 , and 2014 and the related effects on pre-tax income are as follows (in thousands): 2016 2015 2014 Proceeds from sales of available-for-sale securities $ 91,268 $ 102,567 $ 108,311 Gross realized gains included in pre-tax income $ 9,212 $ 12,379 $ 7,858 Gross realized losses included in pre-tax income (1,220 ) (927 ) (508 ) Gross unrealized losses included in pre-tax income (352 ) (338 ) — Net gains in pre-tax income $ 7,640 $ 11,114 $ 7,350 Net unrealized holding gains (losses) included in accumulated other comprehensive income $ 8,444 $ (2,906 ) $ 10,827 Net (gains) losses reclassified out of accumulated other comprehensive income (7,640 ) (11,114 ) (7,350 ) Net gains (losses) in other comprehensive income $ 804 $ (14,020 ) $ 3,477 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 concluded that the NAV used for determining the fair value of the Institutional Funds- International Equity investments have readily determinable fair values. Accordingly, such fund values have been re-categorized from Level 2 to Level 1 hierarchy. • Level 2 - Inputs other than quoted market prices included in Level 1 that are observable for the asset or liability either directly or indirectly. Financial assets utilizing Level 2 inputs include the nuclear decommissioning trust investments in fixed income securities. The fair value of these financial instruments is based on evaluated prices that reflect observable market information, such as actual trade information of similar securities, adjusted for observable differences. • Level 3 - Unobservable inputs using data that is not corroborated by market data and primarily based on internal Company analysis using models and various other analysis. Financial assets utilizing Level 3 inputs are the Company's investment in debt securities. The securities in the Company's decommissioning trust funds are valued using prices and other relevant information generated by market transactions involving identical or comparable securities. The FASB guidance identifies this valuation technique as the "market approach" with observable inputs. The Company analyzes available-for-sale securities to determine if losses are other than temporary. The fair value of the Company’s decommissioning trust funds and investments in debt securities at December 31, 2016 and 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 December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Trading Securities: Investments in Debt Securities $ 1,421 $ — $ — $ 1,421 Available for sale: U.S. Government Bonds $ 61,868 $ 61,868 $ — $ — Federal Agency Mortgage Backed Securities 19,448 — 19,448 — Municipal Obligations 16,144 — 16,144 — Corporate Obligations 22,413 — 22,413 — Subtotal, Debt Securities 119,873 61,868 58,005 — Common Stock 64,644 64,644 — — Equity Mutual Funds 42,244 42,244 — — Institutional Funds-International Equity 22,945 22,945 — — Cash and Cash Equivalents 6,002 6,002 — — Total available for sale $ 255,708 $ 197,703 $ 58,005 $ — 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 Obligations 24,345 — 24,345 — Corporate 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 $ — Below is a reconciliation of the beginning and ending balance of the fair value of the investment in debt securities (in thousands): 2016 2015 Balance at January 1 $ 1,543 $ 1,653 Net unrealized gains (losses) in fair value recognized in income (a) (122 ) (110 ) Balance at December 31 $ 1,421 $ 1,543 _____________________ (a) These amounts are reflected in the Company's statements of operations as investment and interest income. 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 twelve month periods ending December 31, 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 twelve month periods ending December 31, 2016 and 2015 .

Supplemental Statements of Cash

Supplemental Statements of Cash Flows Disclosures	12 Months Ended
	Dec. 31, 2016
Supplemental Cash Flow Information [Abstract]
Cash Flow, Supplemental Disclosures	Supplemental Statements of Cash Flows Disclosures Years Ended December 31, 2016 2015 2014 (In thousands) Cash paid for: Interest on long-term debt and borrowing under the revolving credit facility $ 69,990 $ 62,297 $ 54,792 Income taxes, net of refund 2,328 1,000 6,876 Non-cash investing and financing activities: Sale of Interest in Four Corners Generating Station (a) 27,720 — — Changes in accrued plant additions 4,789 (6,660 ) 7,314 Grants of restricted shares of common stock 1,236 1,567 3,025 (a) The Company sold its interest in Four Corners for approximately $32.0 million based on the book value as defined in the Purchase and Sale Agreement. The sales price was adjusted downward by $7.0 million and $19.5 million to reflect APS's affiliate assumption of the Company's obligation to pay for future plant decommissioning and mine reclamation expense, respectively. The sales price was also adjusted downward by approximately $1.3 million for closing adjustments and other assets and liabilities assumed by APS's affiliate. At the closing of the sale, the Company received approximately $4.2 million in cash, subject to post-closing adjustments.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2016
Selected Quarterly Financial Data
Quarterly Financial Information	Selected Quarterly Financial Data (Unaudited) The following table summarizes the Company’s unaudited results of operations on a quarterly basis. The quarterly earnings per share amounts for a year will not add to the earnings per share for that year due to the weighting of shares used in calculating per share data. 2016 Quarters 2015 Quarters 4th 3rd (2) 2nd 1st 4th 3rd 2nd 1st (In thousands except for share data) Operating revenues (1) $ 188,037 $ 323,225 $ 217,865 $ 157,809 $ 176,902 $ 289,713 $ 219,508 $ 163,746 Operating income (loss) 20,470 129,857 44,697 (163 ) 8,312 88,047 41,872 7,960 Net income (loss) 5,656 74,636 22,284 (5,808 ) 648 56,740 21,072 3,458 Basic earnings per share: Net income (loss) 0.14 1.84 0.55 (0.14 ) 0.02 1.40 0.52 0.09 Diluted earnings per share: Net income (loss) 0.14 1.84 0.55 (0.14 ) 0.02 1.40 0.52 0.09 Dividends declared per share of common stock 0.310 0.310 0.310 0.295 0.295 0.295 0.295 0.280 ________________ (1) Operating revenues are seasonal in nature, with the peak sales periods generally occurring during the summer months. Comparisons among quarters of a year may not represent overall trends and changes in operations. (2) For financial reporting purposes, the Company deferred any recognition of the Company's request in its 2015 Texas Retail Rate Case until it received the PUCT Final Order on August 25, 2016. Accordingly, it reported in the third quarter of 2016 the cumulative effect of the PUCT Final Order which related back to January 12, 2016. See Part II, Item 8, Financial Statements and Supplementary Data, Note C.

Summary of Significant Accoun26

Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Basis of Accounting, Policy	Basis of Presentation . The Company maintains its accounts in accordance with the Uniform System of Accounts prescribed by the Federal Energy Regulatory Commission (the "FERC").
Use of Estimates	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.
Application of FASB Guidance for Regulated Operations	Application of the Financial Accounting Standards Board (the "FASB" ) Guidance for Regulated Operations. Regulated electric utilities typically prepare their financial statements in accordance with the FASB guidance for regulated operations. The FASB guidance for regulated operations requires the Company to include an allowance for equity and borrowed funds used during construction ("AEFUDC" and "ABFUDC") as a cost of construction of electric plant in service. AEFUDC is recognized as income and ABFUDC is shown as capitalized interest charges in the Company’s statements of operations. The FASB guidance for regulated operations also requires the Company to show certain recoverable costs as either assets or liabilities on a utility’s balance sheet if the regulator provides assurance that these costs will be charged to and collected from the utility’s customers (or has already permitted such cost recovery) or will be credited or refunded to the utility’s customers. The resulting regulatory assets or liabilities are amortized in subsequent periods based upon the respective amortization periods reflected in a utility’s regulated rates. See Part II, Item 8, Financial Statements and Supplementary Data, Note D. The Company applies the FASB guidance for regulated operations for all three of the jurisdictions in which it operates.
Comprehensive Income	Comprehensive Income. Certain gains and losses that are not recognized currently in the statements of operations are reported as other comprehensive income in accordance with the FASB guidance for reporting comprehensive income.
Utility plant	Utility Plant. Utility plant is generally reported at cost. The cost of renewals and betterments are capitalized and the costs of repairs and minor replacements are charged to the appropriate operating expense accounts. Depreciation is provided on a straight-line basis over the estimated remaining lives of the assets (ranging in average from 5 to 48 years). The average composite depreciation rate utilized in 2016 , 2015 and 2014 was 2.28% , 2.64% , and 2.60% , respectively. When property subject to composite depreciation is retired or otherwise disposed of in the normal course of business, its cost together with the cost of removal, less salvage is charged to accumulated depreciation. For other property dispositions, the applicable cost and accumulated depreciation is removed from the balance sheet accounts and a gain or loss is recognized. During 2016, depreciation and amortization decreased due to changes in depreciation rates approved in the most recent final orders from the Public Utility Commission of Texas ("PUCT") and the New Mexico Public Regulation Commission ("NMPRC") and changes in the estimated life of certain intangible software assets. See Part II, Item 8, Financial Statements and Supplementary Data, Note C and Note E. Previously, the Company recorded gains and losses on the disposition of vehicles in earnings when realized. However, beginning in 2016, the Company began crediting the proceeds (salvage) on the disposition of vehicles to accumulated depreciation. The cost of nuclear fuel is amortized to fuel expense on a units-of-production basis. The Company is also amortizing its share of costs associated with on-site spent fuel storage casks at Palo Verde Nuclear Generating Station ("Palo Verde") over the burn period of the fuel that will necessitate the use of the storage casks. See Part II, Item 8, Financial Statements and Supplementary Data, Note E.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets. Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated undiscounted future cash flows, an impairment charge is recognized for the amount by which the carrying amount of the asset exceeds the fair value of the asset.
AFUDC and Capitalized Interest	AFUDC and Capitalized Interest . The Company capitalizes interest ("ABFUDC") and common equity ("AEFUDC") costs to construction work in progress and capitalizes interest to nuclear fuel in process in accordance with the FERC Uniform System of Accounts as provided for in the FASB guidance. AFUDC is a non-cash component of income and is calculated monthly and charged to all new eligible construction and capital improvement projects. AFUDC is compounded on a semi-annual basis. The average AFUDC rates used in 2016 , 2015 and 2014 were 6.43% , 7.18% and 8.15% , respectively.
Asset Retirement Obligation	Asset Retirement Obligation. The FASB guidance sets forth accounting requirements for the recognition and measurement of liabilities associated with the retirement of tangible long-lived assets. An ARO associated with long-lived assets included within the scope of the FASB guidance is that for which a legal obligation exists under enacted laws, statutes, written or oral contracts, including obligations arising under the doctrine of promissory estoppel and legal obligations to perform an asset retirement activity even if the timing and/or settlement are conditioned on a future event that may or may not be within the control of an entity. See Part II, Item 8, Financial Statements and Supplementary Data, Note F. Under the FASB guidance, these liabilities are recognized as incurred if a reasonable estimate of fair value can be established and are capitalized as part of the cost of the related tangible long-lived assets. The Company records the increase in the ARO due to the passage of time as an operating expense (accretion expense).
Cash and Cash Equivalents	Cash and Cash Equivalents . All temporary cash investments with an original maturity of three months or less are considered cash equivalents.
Investments	Investments . The Company’s marketable securities, included in decommissioning trust funds in the balance sheet, are reported at fair value and consist of cash, equity securities and municipal, federal and corporate bonds in trust funds established for decommissioning of its interest in Palo Verde. Such marketable securities are classified as "available-for-sale" securities and, as such, unrealized gains and losses are included in accumulated other comprehensive loss as a separate component of common stock equity. However, if declines in the fair value of marketable securities below original cost basis are determined to be other than temporary, the declines are reported as losses in the statements of operations and a new cost basis is established for the affected securities at fair value. Gains and losses are determined using the cost of the security based on the specific identification basis. See Part II, Item 8, Financial Statements and Supplementary Data, Note O.
Derivative Accounting	Derivative Accounting. Accounting for derivative instruments and hedging activities requires the recognition of derivatives as either assets or liabilities in the balance sheet with measurement of those instruments at fair value. Any changes in the fair value of these instruments are recorded in earnings or other comprehensive income. See Part II, Item 8, Financial Statements and Supplementary Data, Note O.
Inventories	Inventories . Inventories, primarily parts, materials, supplies, fuel oil and natural gas are stated at average cost, which is not to exceed recoverable cost.
Operating Revenues Net of Energy Expenses	Operating Revenues Net of Energy Expenses . The Company accrues revenues for services rendered, including unbilled electric service revenues. Energy expenses are stated at actual cost incurred. The Company’s Texas retail customers are billed under base rates and a fixed fuel factor approved by the PUCT. The Company’s New Mexico retail customers are billed under base rates and a fuel adjustment clause which is adjusted monthly, as approved by the NMPRC. The Company's FERC sales for resale customers are billed under formula base rates and fuel factors and a fuel adjustment clause which is adjusted monthly. The Company’s recovery of energy expenses is subject to periodic reconciliations of actual energy expenses incurred to actual fuel revenues collected. The difference between energy expenses incurred and fuel revenues charged to customers is reflected as over/under-collection of fuel revenues in the balance sheets. See Part II, Item 8, Financial Statements and Supplementary Data, Note C. Revenues. Revenues related to the sale of electricity are 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 customers 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 $21.0 million and $21.7 million as of December 31, 2016 and 2015 , respectively. The Company presents revenues net of sales taxes in its statements of operations.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts. The allowance for doubtful accounts represents the Company’s estimate of existing accounts receivable that will ultimately be uncollectible. The allowance is calculated by applying estimated write-off factors to various classes of outstanding receivables. The write-off factors used to estimate uncollectible accounts are based upon consideration of both historical collections experience and management’s best estimate of future collections success given the existing collections environment. Additions, deductions and balances for allowance for doubtful accounts for 2016 , 2015 and 2014 are as follows (in thousands): 2016 2015 2014 Balance at beginning of year $ 2,046 $ 2,253 $ 2,261 Additions: Charged to costs and expense 2,427 2,057 2,755 Recovery of previous write-offs 1,395 1,613 1,516 Uncollectible receivables written off 3,712 3,877 4,279 Balance at end of year $ 2,156 $ 2,046 $ 2,253
Income Taxes	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 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 final orders from the PUCT and the NMPRC in its 2015 rate cases, effective January 1, 2016. See Part II, Item 8, Financial Statements and Supplementary Data, Note C 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 Part II, Item 8, Financial Statements and Supplementary Data, Note J.
Earnings per Share	Earnings per Share . The Company’s restricted stock awards are participating securities and earnings per share must be calculated using the two-class method in both the basic and diluted earnings per share calculations. For the basic earnings per share calculation, net income is allocated to the weighted average number of restricted stock awards and to the weighted average number of shares outstanding. The net income allocated to the weighted average number of shares outstanding is then divided by the weighted average number of shares outstanding to derive the basic earnings per share. For the diluted earnings per share, net income is allocated to the weighted average number of restricted stock awards and to the weighted average number of shares and dilutive potential shares outstanding. The Company’s dilutive potential shares outstanding amount is calculated using the treasury stock method for the unvested performance shares. Net income allocated to the weighted average number of shares and dilutive potential shares is then divided by the weighted average number of shares and dilutive potential shares outstanding to derive the diluted earnings per share. See Part II, Item 8, Financial Statements and Supplementary Data, Note G.
Stock-Based Compensation	Stock-Based Compensation . The Company has a stock-based long-term incentive plan. The Company is required under the FASB guidance to measure the cost of employee services received in exchange for an award of equity instruments based on the grant-date fair value of the award. Such costs are recognized over the period during which an employee is required to provide service in exchange for the award (the "requisite service period") which typically is the vesting period. Compensation cost is not recognized for anticipated forfeitures prior to vesting of equity instruments. See Part II, Item 8, Financial Statements and Supplementary Data, Note G.
Reclassification	Reclassification. Certain amounts in the Company's financial statements for 2015 have been reclassified to conform to the 2016 presentation. The Company implemented Accounting Standards Update ("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 Part II, Item 8, Financial Statements and Supplementary Data, Note I and Note O for impact of ASU 2015-03, and Note J for impact of ASU 2015-17

Utility Plant, Palo Verde and27

Utility Plant, Palo Verde and Other Jointly-Owned Utility Plant Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Depreciation, Depletion, and Amortization	Amortization of intangible plant (software) is provided on a straight-line basis over the estimated useful life of the asset (ranging from 3 to 15 years).

Employee Benefits Pension and O

Employee Benefits Pension and Other Postretirement Benefit Plans Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Pension and Other Postretirement Plans, Pensions, Policy	The Company’s Retirement Income Plan (the "Retirement Plan") is a qualified noncontributory defined benefit plan. Upon retirement or death of a vested plan participant, assets of the Retirement Plan are used to pay benefit obligations under the Retirement Plan. Contributions from the Company are based on various factors such as the minimum funding amounts required by the Internal Revenue Service ("IRS"), state and federal regulatory requirements, amounts collected from customers in the Company's Texas and New Mexico jurisdictions and the annual cost of the Retirement Plan, as actuarially calculated. The assets of the Retirement Plan are primarily invested in common collective trusts which hold equity securities, debt securities and cash equivalents and are managed by a professional investment manager appointed by the Company. The Company has two non-qualified retirement plans that are non-funded defined benefit plans. The Company's Supplemental Retirement Plan covers certain former employees and directors of the Company. The Excess Benefit Plan, was adopted in 2004 and covers certain active and former employees of the Company. The benefit cost for the non-qualified retirement plans are based on substantially the same actuarial methods and economic assumptions as those used for the Retirement Plan. During the quarter ended March 31, 2014 , the Company implemented certain amendments to the Retirement Plan and Excess Benefit Plan. In the first quarter of 2014 , the Company offered a cash balance pension plan as an alternative to its current final average pay pension plan for employees hired prior to January 1, 2014 . The cash balance pension plan also included an enhanced employer matching contribution to the employee’s respective 401(k) Defined Contribution Plan (discussed below). For employees that elected the new cash balance feature of the plans, the pension benefit earned under the existing final average pay feature of the plans was frozen as of March 31, 2014 . Employees hired after January 1, 2014 were automatically enrolled in the cash balance pension plan. The amendments to the plans were effective April 1, 2014 . As a result of these actions, the Company remeasured the assets and liabilities of the plans, based on actuarially determined estimates, using the close of the alternative choice election period of February 28, 2014 , as the remeasurement date. Prior to December 31, 2013 , employees who completed one year of service with the Company and worked at least a minimum number of hours each year were covered by the final average pay formula of the plan. For participants that continue to be covered by the final average pay formula, retirement benefits are based on the employee’s final average pay and years of service. The cash balance pension plan covers employees beginning on their employment commencement date or re-employment commencement date in any plan year in which the employee completes at least a minimum number of hours of service. Retirement benefits under the cash balance pension plan are based on the employee’s cash balance account, consisting of pay credits and interest credits.
Pension and Other Postretirement Plans, Nonpension Benefits, Policy	The Company provides certain health care benefits for retired employees and their eligible dependents and life insurance benefits for retired employees only. Substantially all of the Company’s employees may become eligible for those benefits if they retire while working for the Company.

Summary of Significant Accoun29

Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Allowance for Doubtful Accounts Receivable	Additions, deductions and balances for allowance for doubtful accounts for 2016 , 2015 and 2014 are as follows (in thousands): 2016 2015 2014 Balance at beginning of year $ 2,046 $ 2,253 $ 2,261 Additions: Charged to costs and expense 2,427 2,057 2,755 Recovery of previous write-offs 1,395 1,613 1,516 Uncollectible receivables written off 3,712 3,877 4,279 Balance at end of year $ 2,156 $ 2,046 $ 2,253

Regulatory Assets and Liabili30

Regulatory Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2016
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets and Liabilities	Regulatory assets and liabilities reflected in the Company's balance sheet are presented below (in thousands): Amortization Period Ends December 31, 2016 December 31, 2015 Regulatory assets Regulatory tax assets (a) (b) $ 66,670 $ 69,359 Loss on reacquired debt (c) May 2035 15,780 16,632 Final coal reclamation (d) (e) 9,581 9,520 Nuclear fuel postload daily financing charge (e) 3,831 4,195 Unrecovered issuance costs due to reissuance of PCBs (c) August 2042 794 827 Texas energy efficiency (f) — 25 Texas 2015 rate case costs September 2018 2,670 1,882 Texas 2017 rate case costs (g) 246 — Texas relate back surcharge (h) 6,455 — New Mexico renewable energy credits and related costs (i) June 2022 6,937 6,397 New Mexico 2010 FPPCAC audit June 2019 398 434 New Mexico Palo Verde deferred depreciation (b) 4,415 4,568 New Mexico 2015 rate case costs June 2019 1,074 1,288 New Mexico 2017 rate case costs (g) 10 — Total regulatory assets $ 118,861 $ 115,127 Regulatory liabilities Regulatory tax liabilities (a) (b) $ 10,648 $ 17,266 Accumulated deferred investment tax credit (j) (b) 3,328 4,011 Texas energy efficiency (f) 1,288 — New Mexico energy efficiency (f) 2,159 2,238 Texas military base discount and recovery factor (k) 184 788 New Mexico gain on sale of assets (l) June 2019 828 — Total regulatory liabilities $ 18,435 $ 24,303 ______________________________ (a) We do not earn a return on these items since the related accumulated deferred income tax assets and liabilities offset. (b) The amortization periods for these assets and liabilities are based upon the life of the associated assets or liabilities. (c) This item is recovered as a component of the weighted cost of debt and amortized over the life of the related debt issuance. (d) This item relates to coal reclamation costs associated with Four Corners. See Part II, Item 8, Financial Statements and Supplementary Data, Note C. (e) This item is recovered through fuel recovery mechanisms established by tariffs. (f) This item is recovered or credited through a recovery factor that is set annually. (g) Amortization period is anticipated to be established in next general rate case. (h) This item relates to the recovery of revenues through a separate surcharge beginning October 1, 2016 and ending September 30, 2017. See Part II, Item 8, Financial Statements and Supplementary Data, Note C. (i) This item relates to renewable energy credits and procurement plan costs, components approved for recovery in the New Mexico 2015 rate case. (j) This item is excluded from rate base. (k) This item represents the net asset/net liability related to the military discount which is recovered from non-military customers through a recovery factor that is set annually. (l) This item relates to the gains on the sales of assets the Company shares with its New Mexico customers over a three year period.

Utility Plant, Palo Verde and31

Utility Plant, Palo Verde and Other Jointly-Owned Utility Plant (Tables)	12 Months Ended
	Dec. 31, 2016
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Schedule of Property, Plant and Equipment and Finite-Lived Intangible Assets By Major Class	The table below presents the balance of each major class of depreciable assets at December 31, 2016 (in thousands): Gross Plant Accumulated Depreciation Net Plant Nuclear production $ 948,382 $ (320,000 ) $ 628,382 Steam and other 926,419 (186,539 ) 739,880 Total production 1,874,801 (506,539 ) 1,368,262 Transmission 498,660 (259,488 ) 239,172 Distribution 1,127,897 (365,601 ) 762,296 General 205,866 (57,240 ) 148,626 Intangible 84,342 (55,464 ) 28,878 Total $ 3,791,566 $ (1,244,332 ) $ 2,547,234
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	The table below presents the actual and estimated amortization expense for intangible plant for the previous three years and for the next five years (in thousands): 2014 $ 8,051 2015 6,482 2016 5,302 2017 (estimated) 5,148 2018 (estimated) 4,631 2019 (estimated) 4,242 2020 (estimated) 3,808 2021 (estimated) 3,227
Schedule of Jointly Owned Utility Plants	A summary of the Company’s investment in jointly-owned utility plant, excluding fuel inventories, at December 31, 2016 and 2015 is as follows (in thousands): December 31, 2016 December 31, 2015 Palo Verde Other (a) Palo Verde Other (a) Electric plant in service $ 948,382 $ 67,621 $ 917,483 $ 229,627 Accumulated depreciation (320,000 ) (44,377 ) (304,060 ) (181,886 ) Construction work in progress 50,598 1,895 48,938 9,528 Total $ 678,980 $ 25,139 $ 662,361 $ 57,269 _______________ (a) 2015 other jointly-owned utility plant includes a 7% interest in Units 4 and 5 at Four Corners and certain other transmission facilities which the Company sold on July 6, 2016.

Accounting for Asset Retireme32

Accounting for Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2016
Accounting for Asset Retirement Obligations
Changes In Estimated Probabilities Assumptions	The assumptions used to calculate the Palo Verde ARO liability are as follows: Escalation Rate Credit-Risk Adjusted Discount Rate Original ARO liability 3.60 % 9.50 % Incremental ARO liability 3.60 % 6.20 %
Schedule of Asset Retirement Obligations	2016 2015 2014 ARO liability at beginning of year $ 81,621 $ 74,577 $ 65,214 Liabilities incurred — 189 — Liabilities settled (6,993 ) — — Revisions to estimate — — 3,561 Accretion expense 7,172 6,855 5,802 ARO liability at end of year $ 81,800 $ 81,621 $ 74,577

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Treasury Stock by Class	Detail regarding the Company's stock repurchase program are presented below: Since 1999 Authorized Shares repurchased (b) 25,406,184 Cost, including commission (in thousands) $ 423,647 Total remaining shares available for repurchase at December 31, 2016 393,816 ______________________ (a) Represents repurchased shares and cost since inception of the stock repurchase program in 1999. (b) Shares repurchased does not include 86,735 treasury shares related to employee compensation arrangements outside of the Company's repurchase programs. Beginning in 2015, shares of the Company's common stock issued for employee benefit and stock incentive plans have been issued from the shares repurchased and held in treasury stock. The Company awarded 188,005 shares out of treasury stock during 2016.
Schedule of Earnings Per Share, Basic and Diluted	The basic and diluted earnings per share are presented below: Years Ended December 31, 2016 2015 2014 Weighted average number of common shares outstanding: Basic number of common shares outstanding 40,350,688 40,274,986 40,190,991 Dilutive effect of unvested performance awards 57,345 33,576 20,726 Diluted number of common shares outstanding 40,408,033 40,308,562 40,211,717 Basic net income per common share: Net income $ 96,768 $ 81,918 $ 91,428 Income allocated to participating restricted stock (321 ) (243 ) (301 ) Net income available to common shareholders $ 96,447 $ 81,675 $ 91,127 Diluted net income per common share: Net income $ 96,768 $ 81,918 $ 91,428 Income reallocated to participating restricted stock (321 ) (243 ) (301 ) Net income available to common shareholders $ 96,447 $ 81,675 $ 91,127 Basic net income per common share: Distributed earnings $ 1.225 $ 1.165 $ 1.105 Undistributed earnings 1.165 0.865 1.165 Basic net income per common share $ 2.390 $ 2.030 $ 2.270 Diluted net income per common share: Distributed earnings $ 1.225 $ 1.165 $ 1.105 Undistributed earnings 1.165 0.865 1.165 Diluted net income per common share $ 2.390 $ 2.030 $ 2.270
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: Year Ended December 31, 2016 2015 2014 Restricted stock awards 53,703 56,375 60,455 Performance shares (a) 47,246 66,804 96,208 _____________________ (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.
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Expense, Deferred Tax Benefit, and Current Tax Expense Related to Restricted Stock Awards	The expense, deferred tax benefit, and current tax expense recognized related to restricted stock and other stock-based awards in 2016 , 2015 and 2014 is presented below (in thousands): 2016 2015 2014 Expense (a) $ 2,594 $ 2,755 $ 3,471 Deferred tax benefit 908 964 1,215 Current tax benefit recognized 183 43 39 _____________________ (a) Any capitalized costs related to these expenses is less than $0.3 million for all years.
Schedule of Restricted Stock Activity	The unvested restricted stock transactions for 2016 are presented below: Total Shares Weighted Average Grant Date Fair Value Unrecognized Compensation Expense (a) Aggregate Intrinsic Value (In thousands) (In thousands) Restricted shares outstanding at December 31, 2015 91,210 $ 36.61 Stock awards 74,181 40.95 Vested (55,503 ) 35.91 Forfeitures (495 ) 36.88 Restricted shares outstanding at December 31, 2016 109,393 39.90 $ 1,767 $ 5,087 _______________________ (a) The unrecognized compensation expense is expected to be recognized over the weighted average remaining contractual term of the outstanding restricted stock of approximately one year.
Schedule of Share-based Compensation Award, Restricted Stock, Grants in Period, Weighted Average Grant Date Fair Value	The weighted average fair value per share at grant date for restricted stock and other stock-base awards granted during 2016 , 2015 and 2014 were: 2016 2015 2014 Weighted average fair value per share $ 40.95 $ 37.17 $ 36.95
Schedule of Share-based Compensation, Activity	The aggregate intrinsic value and fair value at grant date of restricted stock and other stock-based awards which vested in 2016 , 2015 and 2014 is presented below (in thousands): 2016 2015 2014 Aggregated intrinsic value $ 2,515 $ 3,451 $ 3,441 Fair value at grant date 1,993 3,327 3,330
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Share-based Compensation Award, Performance-Based Units, Vested and Expected to Vest	Detail of performance shares vested follows: Date Vested Payout Ratio Performance Shares Awarded Compensation Costs Expensed Period Compensation Costs Expensed Aggregated Intrinsic Value (In thousands) (In thousands) January 25, 2017 32 % 11,314 $ 932 2014-2016 $ 512 January 27, 2016 0 % 0 851 2013-2015 — February 20, 2015 0 % 0 1,502 2012-2014 — February 18, 2014 0 % 0 954 2011-2013 —
Schedule of Performance Stock Activity	The outstanding performance share awards at the 100% performance level is summarized below: Number Outstanding Weighted Average Grant Date Fair Value Unrecognized Compensation Expense (b) Aggregate Intrinsic Value (In thousands) (In thousands) Performance shares outstanding at December 31, 2015 (a) 130,136 $ 32.72 Performance share awards 60,835 38.11 Performance shares expired (24,527 ) 34.69 Performance shares outstanding at December 31, 2016 (a) 166,444 34.40 $ 2,189 $ 7,740 _______________________ (a) On December 15, 2015, the Company issued a stock based retention grant to the Chief Executive Officer (CEO) of 27,624 shares in accordance with the Amended and Restated 2007 LTIP that is eligible for vesting based on the achievement of certain performance conditions and a five year service period, as stated in the CEO's employment agreement. The performance condition was met as of November 2016 as determined by the Compensation Committee, and has been included in the beginning and ending balance in the table above. (b) The unrecognized compensation expense is expected to be recognized over the weighted average remaining contractual term of the awards of approximately one year, except for the CEO retention grant.
Schedule of Share-based Compensation, Activity	A summary of information related to performance shares for 2016 , 2015 and 2014 is presented below: 2016 2015 2014 Weighted average per share grant date fair value per share of performance shares awarded $ 38.11 $ 35.72 $ 26.36 Compensation expense (in thousands) (a) (b) 1,655 1,042 1,181 Deferred tax benefit related to compensation expense (in thousands) (b) 579 365 413 _____________________ (a) Includes adjustments for estimated forfeitures. (b) Includes CEO retention grant.

Accumulated Other Comprehensi34

Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 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): 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 December 31, 2013 $ (21,330 ) $ 36,240 $ (12,298 ) $ 2,612 Other comprehensive income (loss) before reclassifications (12,628 ) 8,694 — (3,934 ) Amounts reclassified from accumulated other comprehensive income (loss) (926 ) (5,977 ) 224 (6,679 ) Balance at December 31, 2014 (34,884 ) 38,957 (12,074 ) (8,001 ) Other comprehensive income (loss) before reclassifications 3,777 (2,255 ) — 1,522 Amounts reclassified from accumulated other comprehensive income (loss) 1,238 (8,937 ) 264 (7,435 ) Balance at December 31, 2015 (29,869 ) 27,765 (11,810 ) (13,914 ) Other comprehensive income before reclassifications 7,363 6,904 — 14,267 Amounts reclassified from accumulated other comprehensive income (loss) (1,422 ) (6,206 ) 159 (7,469 ) Balance at December 31, 2016 $ (23,928 ) $ 28,463 $ (11,651 ) $ (7,116 )
Reclassification out of Accumulated Other Comprehensive Income	Amounts reclassified from Accumulated Other Comprehensive Income (Loss) for the twelve months ended December 31, 2016 , 2015 and 2014 are as follows (in thousands): Details about Accumulated Other Comprehensive Income (Loss) Components 2016 2015 2014 Affected Line Item in the Statements of Operations Amortization of pension and post-retirement benefit costs: Prior service benefit $ 7,407 $ 6,574 $ 7,659 (a) Net loss (4,965 ) (8,622 ) (6,182 ) (a) 2,442 (2,048 ) 1,477 (a) Income tax effect (1,020 ) 810 (551 ) Income tax expense 1,422 (1,238 ) 926 Net income Marketable securities: Net realized gain on sale of securities 7,640 11,114 7,350 Investment and interest income, net 7,640 11,114 7,350 Income before income taxes Income tax effect (1,434 ) (2,177 ) (1,373 ) Income tax expense 6,206 8,937 5,977 Net income Loss on cash flow hedge: Amortization of loss (498 ) (467 ) (438 ) Interest on long-term debt and revolving credit facility (498 ) (467 ) (438 ) Income before income taxes Income tax effect 339 203 214 Income tax expense (159 ) (264 ) (224 ) Net income Total reclassifications $ 7,469 $ 7,435 $ 6,679 (a) These items are included in the computation of net periodic benefit cost. See Part II, Item 8, Financial Statements and Supplementary Data, Note M for additional information.

Long-Term Debt and Financing 35

Long-Term Debt and Financing Obligations (Tables)	12 Months Ended
	Dec. 31, 2016
Long-Term Debt and Financing Obligations [Abstract]
Schedule of Debt	Outstanding long-term debt and financing obligations are as follows: December 31, 2016 2015 (1) (In thousands) Long-Term Debt: Pollution Control Bonds (2): 7.25% 2009 Series A refunding bonds, due 2040 (7.46% effective interest rate) $ 62,619 $ 62,582 4.50% 2012 Series A refunding bonds, due 2042 (4.63% effective interest rate) 58,471 58,441 7.25% 2009 Series B refunding bonds, due 2040 (7.49% effective interest rate) 36,492 36,465 1.875% 2012 Series A refunding bonds, due 2032 (2.35% effective interest rate) 33,193 33,011 Total Pollution Control Bonds 190,775 190,499 Senior Notes (3): 6.00% Senior Notes, net of discount, due 2035 (7.12% effective interest rate) 393,861 393,693 7.50% Senior Notes, net of discount, due 2038 (7.67% effective interest rate) 147,331 147,282 3.30% Senior Notes, net of discount, due 2022 (3.43% effective interest rate) 148,939 148,783 5.00% Senior Notes, net of discount, due 2044 (4.93% effective interest rate) 302,955 147,717 Total Senior Notes 993,086 837,475 RGRT Senior Notes (4): 4.47% Senior Notes, Series B, due 2017 (4.62% effective interest rate) 49,950 49,883 5.04% Senior Notes, Series C, due 2020 (5.16% effective interest rate) 44,845 44,803 Total RGRT Senior Notes 94,795 94,686 Total long-term debt 1,278,656 1,122,660 Financing Obligations: Revolving Credit Facility ($81,574 due in 2017) (5) 81,574 141,738 Total long-term debt and financing obligations 1,360,230 1,264,398 Current Portion (amount due within one year): Current maturities of long term debt (83,143 ) — Short-term borrowings under the revolving credit facility (81,574 ) (141,738 ) $ 1,195,513 $ 1,122,660 _____________________ (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) Pollution Control Bonds ("PCBs") The Company has four series of tax exempt unsecured PCBs in aggregate principal amount of $193.1 million . The 1.875% 2012 Series A (El Paso Electric Company Four Corners Project) Pollution Control Refunding Revenue Bonds with an aggregate principal amount of $33.3 million are subject to mandatory tender for purchase in September 2017 at which time the Company will either repay or remarket these bonds. (3) Senior Notes The Senior Notes are unsecured obligations of the Company. They were issued pursuant to bond covenants that provide limitations on the Company’s ability to enter into certain transactions. The 6.00% Senior Notes have an aggregate principal amount of $400.0 million and were issued in May 2005 . The proceeds, net of a $2.3 million discount, were used to fund the retirement of the Company's first mortgage bonds. The Company amortizes the loss associated with a cash flow hedge recorded in accumulated other comprehensive income to earnings as interest expense over the life of the 6.00% Senior Notes. See Part II, Item 8, Financial Statements and Supplementary Data, Note O. This amortization is included in the effective interest rate of the 6.00% Senior Notes. The 7.50% Senior Notes have an aggregate principal amount of $150.0 million and were issued in June 2008 . The proceeds, net of a $1.3 million discount, were used to repay short-term borrowings of $44.0 million , fund capital expenditures and for other general corporate purposes. The 3.30% Senior Notes have an aggregate principal amount of $150.0 million were issued in December 2012 . The proceeds, net of a $0.3 million discount, were used to fund construction expenditures and for working capital and general corporate purposes. In December 2014 , the Company issued 5.00% Senior Notes with an aggregate principal amount of $150.0 million . The proceeds, net of a $0.5 million discount, were used to fund construction expenditures and for working capital and general corporate purposes. In March 2016 , the Company issued additional 5.00% Senior Notes with an aggregate principal amount of $150.0 million . The proceeds from this issuance, after deducting the underwriters' commission, were $158.1 million . These proceeds included accrued interest of $2.4 million and a $7.1 million premium before expenses. The net proceeds, from the sale of these senior notes were used to repay outstanding short-term borrowings under the RCF. After the March 2016 issuance, the Company's 5.00% Senior Notes due 2044 had a total principal amount outstanding of $300.0 million . (4) RGRT Senior Notes In 2010, the Company and RGRT, a Texas grantor trust through which the Company finances its portion of fuel for Palo Verde, entered into a note purchase agreement with various institutional purchasers. Under the terms of the agreement, RGRT sold to the purchasers $110 million aggregate principal amount of Senior Notes (the "Notes"). In August 2015 , $15.0 million of these Notes matured and were paid with borrowings from the RCF. In August 2017 , $50.0 million of these Senior Notes will mature. The Company will either repay or refinance this $50.0 million of Notes upon maturity. The Company guarantees the payment of principal and interest on the Notes. In the Company’s financial statements, the assets and liabilities of RGRT are reported as assets and liabilities of the Company. RGRT pays interest on the Notes on February 15, and August 15 of each year until maturity. RGRT may redeem the Notes, in whole or in part, at any time at a redemption price equal to 100% of the principal amount to be redeemed together with the interest on such principal amount accrued to the date of redemption, plus a make-whole amount based on the prevailing market interest rates. The agreement requires compliance with certain covenants, including a total debt to capitalization ratio. The Company was in compliance with these requirements throughout 2016. The sale of the Notes was made by RGRT in reliance on a private placement exemption from registration under the Securities Act of 1933, as amended. The proceeds of $109.4 million , net of issuance costs, from the sale of the Notes was used by RGRT to repay amounts borrowed under the RCF and will enable future nuclear fuel financing requirements of RGRT to be met with a combination of the Notes and amounts borrowed from the RCF. (5) Revolving Credit Facility On January 14, 2014, the Company and RGRT entered into a second amended and restated credit agreement related to the RCF with JP Morgan Chase Bank, N.A., as administrative agent and issuing bank, and Union Bank, N.A., as syndication agent, and various lending banks party thereto. As of December 31, 2016, the Company had available $300 million and the ability to increase the RCF by up to $100 million with a term ending January 2019 . On January 9, 2017, the Company exercised its option to extend the maturity of the RCF by one year to January 14, 2020 and to increase the size of the facility by $50 million to $350 million . The Company still has the option to extend the facility by one additional year to January 2021 and to increase the RCF by up to $50 million (up to a total of $400 million ) upon the satisfaction of certain conditions, more fully set forth in the agreement, including obtaining commitments from lenders or third party financial institutions. The RCF provides that amounts borrowed by the Company may be used for, among other things, working capital and general corporate purposes. Any amounts borrowed by RGRT may be used, among other things, to finance the acquisition and processing of nuclear fuel. Amounts borrowed by RGRT are guaranteed by the Company and the balance borrowed under the RCF is recorded as short-term borrowings on the balance sheet. The RCF is unsecured. The RCF requires compliance with certain covenants, including a total debt to capitalization ratio. The Company was in compliance with these requirements throughout 2016. In August 2015 , $15.0 million aggregate principal amount of Series A 3.67% Senior Notes of RGRT matured and were paid utilizing borrowings under the RCF. As of December 31, 2016 , the total amount borrowed by RGRT was $37.6 million for nuclear fuel under the RCF. As of December 31, 2016 , $44.0 million of borrowings were outstanding under this facility for working capital and general corporate purposes. The weighted average interest rate on the RCF was 2.0% as of December 31, 2016 .
Schedule of Maturities of Long-term Debt	As of December 31, 2016 , the principal amount of scheduled maturities for the next five years of long-term debt are as follows (in thousands): 2017 $ 83,300 2018 — 2019 — 2020 45,000 2021 —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Taxes [Abstract]
Schedule of Deferred Tax Assets and Liabilities	The tax effects of temporary differences that give rise to significant portions of the deferred tax assets and liabilities at December 31, 2016 and 2015 are presented below (in thousands): December 31, 2016 2015 Deferred tax assets: Benefit of tax loss carryforwards $ 60,749 $ 35,153 Alternative minimum tax credit carryforward 16,620 16,620 Pensions and benefits 57,756 61,673 Asset retirement obligation 26,929 28,042 Deferred fuel — 1,488 Other (200 ) 15,421 Total gross deferred tax assets 161,854 158,397 Deferred tax liabilities: Plant, principally due to depreciation and basis differences (668,303 ) (608,738 ) Decommissioning (43,463 ) (41,100 ) Deferred fuel (3,962 ) — Other (1,192 ) (3,796 ) Total gross deferred tax liabilities (716,920 ) (653,634 ) Net accumulated deferred income taxes $ (555,066 ) $ (495,237 )
Schedule of Components of Income Tax Expense (Benefit)	The Company recognized income tax expense for 2016 , 2015 and 2014 as follows (in thousands): Years Ended December 31, 2016 2015 2014 Income tax expense: Federal: Current $ 2,642 $ 2,319 $ (1,250 ) Deferred 47,909 32,819 38,810 Total federal income tax 50,551 35,138 37,560 State: Current 766 1,730 3,209 Deferred 3,285 (1,650 ) 641 Total state income tax 4,051 80 3,850 Generation (amortization) of accumulated investment tax credits (684 ) (323 ) (322 ) Total income tax expense $ 53,918 $ 34,895 $ 41,088
Schedule of Effective Income Tax Rate Reconciliation	Income tax provisions differ from amounts computed by applying the statutory federal income tax rate of 35% to book income before federal income tax as follows (in thousands): Years Ended December 31, 2016 2015 2014 Federal income tax expense computed on income at statutory rate $ 52,740 $ 40,885 $ 46,381 Difference due to: State taxes, net of federal benefit 2,633 52 1,902 AEFUDC (475 ) (2,345 ) (3,757 ) Permanent tax differences (2,369 ) (2,898 ) (2,921 ) Other 1,389 (799 ) (517 ) Total income tax expense $ 53,918 $ 34,895 $ 41,088 Effective income tax rate 35.8 % 29.9 % 31.0 %
Summary of Income Tax Contingencies	A reconciliation of the December 31, 2016 , 2015 and 2014 amounts of unrecognized tax benefits are as follows (in thousands): 2016 2015 2014 Balance at January 1 $ 6,000 $ 5,200 $ 7,200 Additions for tax positions related to the current year 400 500 300 Reductions for tax positions related to the current year — — — Additions for tax positions of prior years 100 300 2,200 Reductions for tax positions of prior years (1,200 ) — (4,500 ) Balance at December 31 $ 5,300 $ 6,000 $ 5,200

Commitments, Contingencies an37

Commitments, Contingencies and Uncertainties (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Long-term Purchase and Sale Commitment	The Company has entered into the following significant agreements with various counterparties for the purchase and sale of electricity: Commercial Operation Type of Contract Counterparty Quantity Term Date Power Purchase and Sale Agreement Freeport 25 MW December 2008 through December 2018 N/A Power Purchase and Sale Agreement Freeport 100 MW June 2006 through December 2021 N/A Power Purchase Agreement Hatch Solar Energy Center I, LLC 5 MW July 2011 through June 2036 July 2011 Power Purchase Agreement NRG 20 MW August 2011 through August 2031 August 2011 Power Purchase Agreement SunE EPE1, LLC 10 MW June 2012 through June 2037 June 2012 Power Purchase Agreement SunE EPE2, LLC 12 MW May 2012 through May 2037 May 2012 Power Purchase Agreement Macho Springs Solar, LLC 50 MW May 2014 through April 2034 May 2014 Power Purchase Agreement Newman Solar LLC 10 MW December 2014 through November 2044 December 2014
Schedule of Future Minimum Rental Payments for Operating Leases	As of December 31, 2016 , the Company’s minimum future rental payments for the next five years are as follows (in thousands): 2017 $ 808 2018 662 2019 666 2020 664 2021 562

Employee Benefits (Tables)

Employee Benefits (Tables)	12 Months Ended
	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Schedule of Amount Recognized in Accumulated Other Comprehensive Income (Loss)	Changes in Accumulated Other Comprehensive Income (Loss) (net of tax) by component are presented below (in thousands): 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 December 31, 2013 $ (21,330 ) $ 36,240 $ (12,298 ) $ 2,612 Other comprehensive income (loss) before reclassifications (12,628 ) 8,694 — (3,934 ) Amounts reclassified from accumulated other comprehensive income (loss) (926 ) (5,977 ) 224 (6,679 ) Balance at December 31, 2014 (34,884 ) 38,957 (12,074 ) (8,001 ) Other comprehensive income (loss) before reclassifications 3,777 (2,255 ) — 1,522 Amounts reclassified from accumulated other comprehensive income (loss) 1,238 (8,937 ) 264 (7,435 ) Balance at December 31, 2015 (29,869 ) 27,765 (11,810 ) (13,914 ) Other comprehensive income before reclassifications 7,363 6,904 — 14,267 Amounts reclassified from accumulated other comprehensive income (loss) (1,422 ) (6,206 ) 159 (7,469 ) Balance at December 31, 2016 $ (23,928 ) $ 28,463 $ (11,651 ) $ (7,116 )
Retirement Income Plan
Defined Benefit Plan Disclosure [Line Items]
Schedule of Net Funded Status	The obligations and funded status of the plans are presented below (in thousands): December 31, 2016 2015 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Change in projected benefit obligation: Benefit obligation at end of prior year $ 325,706 $ 26,958 $ 341,133 $ 28,397 Service cost 7,705 296 8,530 262 Interest cost 12,161 878 13,477 1,018 Actuarial (gain) loss 7,988 1,267 (19,290 ) (810 ) Benefits paid (15,792 ) (1,937 ) (18,144 ) (1,909 ) Benefit obligation at end of year 337,768 27,462 325,706 26,958 Change in plan assets: Fair value of plan assets at end of prior year 260,035 — 272,939 — Actual return (loss) on plan assets 18,223 — (3,760 ) — Employer contribution 7,300 1,937 9,000 1,909 Benefits paid (15,792 ) (1,937 ) (18,144 ) (1,909 ) Fair value of plan assets at end of year 269,766 — 260,035 — Funded status at end of year $ (68,002 ) $ (27,462 ) $ (65,671 ) $ (26,958 )
Schedule of Amounts Recognized in Balance Sheet	Amounts recognized in the Company's balance sheets consist of the following (in thousands): December 31, 2016 2015 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Current liabilities $ — $ (2,696 ) $ — $ (2,102 ) Noncurrent liabilities (68,002 ) (24,766 ) (65,671 ) (24,856 ) Total $ (68,002 ) $ (27,462 ) $ (65,671 ) $ (26,958 )
Schedule of Accumulated Benefit Obligations in Excess of Fair Value of Plan Assets	The accumulated benefit obligation in excess of plan assets is as follows (in thousands): December 31, 2016 2015 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Projected benefit obligation $ (337,768 ) $ (27,462 ) $ (325,706 ) $ (26,958 ) Accumulated benefit obligation (314,071 ) (25,550 ) (302,446 ) (25,785 ) Fair value of plan assets 269,766 — 260,035 —
Schedule of Amounts Recognized in Accumulated Other Comprehensive Income (Loss)	Pre-tax amounts recognized in accumulated other comprehensive income consist of the following (in thousands): Years Ended December 31, 2016 2015 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Net loss $ 121,052 $ 10,073 $ 118,963 $ 9,592 Prior service benefit (23,877 ) (185 ) (27,344 ) (224 ) Total $ 97,175 $ 9,888 $ 91,619 $ 9,368
Schedule of Net Periodic Benefit Costs	The components of net periodic benefit cost are presented below (in thousands): Years Ended December 31, 2016 2015 2014 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Service cost $ 7,705 $ 296 $ 8,530 $ 262 $ 8,284 $ 303 Interest cost 12,161 878 13,477 1,018 14,001 1,041 Expected return on plan assets (18,879 ) — (19,795 ) — (18,699 ) — Amortization of: Net loss 6,554 785 9,710 937 8,178 675 Prior service benefit (3,467 ) (39 ) (3,467 ) (39 ) (2,889 ) (17 ) Net periodic benefit cost $ 4,074 $ 1,920 $ 8,455 $ 2,178 $ 8,875 $ 2,002
Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income (Loss)	The changes in benefit obligations recognized in other comprehensive income are presented below (in thousands): Years Ended December 31, 2016 2015 2014 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Net (gain) loss $ 8,644 $ 1,266 $ 4,266 $ (811 ) $ 47,324 $ 3,508 Prior service benefit — — — — (33,700 ) (500 ) Amortization of: Net loss (6,554 ) (785 ) (9,710 ) (937 ) (8,178 ) (675 ) Prior service benefit 3,467 39 3,467 39 2,889 17 Total recognized in other comprehensive income $ 5,557 $ 520 $ (1,977 ) $ (1,709 ) $ 8,335 $ 2,350
Schedule of Recognized Net Periodic Benefit Obligation and Other Comprehensive Income	The total amount recognized in net periodic benefit costs and other comprehensive income are presented below (in thousands): Years Ended December 31, 2016 2015 2014 Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Retirement Income Plan Non-Qualified Retirement Plans Total recognized in net periodic benefit cost and other comprehensive income $ 9,631 $ 2,440 $ 6,478 $ 469 $ 17,210 $ 4,352
Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year	The following are amounts in accumulated other comprehensive income that are expected to be recognized as components of net periodic benefit cost during 2017 (in thousands): Retirement Income Plan Non-Qualified Retirement Plans Net loss $ 7,530 $ 825 Prior service benefit (3,470 ) (40 )
Schedule of Allocation of Plan Assets	The Company’s target allocations for the plan’s assets are presented below: December 31, 2016 Equity securities 50 % Fixed income 40 % Alternative investments 10 % Total 100 %
Fair Value, Measurement Inputs, Disclosure	The fair value of the Company’s Retirement Plan assets at December 31, 2016 and 2015 , and the level within the three levels of the fair value hierarchy defined by the FASB guidance on fair value measurements are presented in the table below (in thousands): Description of Securities Fair Value as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and Cash Equivalents $ 932 $ 932 $ — $ — Common Collective Trusts (a) Equity funds 144,081 144,081 — — Fixed income funds 109,356 109,356 — — Real Estate Funds 8,406 8,406 — — Total Common Collective Trusts 261,843 261,843 — — Limited Partnership Interest in Real Estate (b)(c) 6,991 Total Plan Investments $ 269,766 $ 262,775 $ — $ — 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) Cash and Cash Equivalents $ 1,266 $ 1,266 $ — $ — Common Collective Trusts (a) Equity funds 144,279 144,279 — — Fixed income funds 103,877 103,877 — — Real Estate Funds 2,025 2,025 — — Total Common Collective Trusts 250,181 250,181 — — Limited Partnership Interest in Real Estate (b)(c) 8,588 Total Plan Investments $ 260,035 $ 251,447 $ — $ — _____________________ (a) The Common Collective Trusts are invested in equity and fixed income securities, or a combination thereof. The investment objective of each fund is to produce returns in excess of, or commensurate with, its predefined index. (b) This investment is a commercial real estate partnership that purchases land, develops limited infrastructure, and sells it for commercial development. The Company was restricted from selling its partnership interest during the life of the partnership, which spanned 7 years. Return on investment is realized as land is sold. The fair value of the limited partnership interest in real estate is based on the NAV of the partnership which reflects the appraised value of the land. The partnership term expired on June 30, 2016 . Upon expiration, dissolution of the partnership commenced and, as a result, the general partner of the partnership is attempting to sell the remaining inventory as soon as possible at the highest pricing possible. (c) In the first quarter of 2016, the Company implemented ASU 2015-07, Fair Value Measurement (Topic 820) which eliminates the requirement to categorize investments in the fair value hierarchy if the fair value is measured at NAV per share (or its equivalent) using the practical expedient in the FASB’s fair value measurement gui dance . The fair value amounts presented in the table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the statement of financial position. ASU 2015-07 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years.
Changes in Fair Value of Investments in Real Estate	The table below reflects the changes in the fair value of investments in the real estate limited partnership during the period (in thousands): Fair Value of Investments in Real Estate Balances at December 31, 2014 $ 8,748 Unrealized loss in fair value (160 ) Balances at December 31, 2015 8,588 Sale of land (775 ) Unrealized loss in fair value (822 ) Balances at December 31, 2016 $ 6,991
Schedule of Expected Benefit Payments	The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid (in thousands): Retirement Income Plan Non-Qualified Retirement Plans 2017 $ 16,113 $ 2,698 2018 19,080 2,060 2019 18,771 2,025 2020 18,923 1,957 2021 19,755 1,907 2022-2026 107,916 8,949
Retirement Income Plan | Benefit Obligations
Defined Benefit Plan Disclosure [Line Items]
Schedule of Assumptions Used	The following are the weighted-average actuarial assumptions used to determine the benefit obligations: December 31, 2016 2015 Non-Qualified Non-Qualified Retirement Income Plan Supplemental Retirement Plan Excess Benefit Plan Retirement Income Plan Supplemental Retirement Plan Excess Benefit Plan Discount rate 4.29 % 3.76 % 4.34 % 4.57 % 3.99 % 4.59 % Rate of compensation increase 4.5 % N/A 4.5 % 4.5 % N/A 4.5 %
Retirement Income Plan | Net Periodic Benefit Costs
Defined Benefit Plan Disclosure [Line Items]
Schedule of Assumptions Used	The following are the weighted-average actuarial assumptions used to determine the net periodic benefit cost for the twelve months ended December 31 : 2016 2015 2014 (a) Non-Qualified Non-Qualified Non-Qualified Retirement Income Plan Supplemental Retirement Plan Excess Benefit Plan Retirement Income Plan Supplemental Retirement Plan Excess Benefit Plan Retirement Income Plan Supplemental Retirement Plan Excess Benefit Plan Discount rate Benefit obligation 4.57 % 3.99 % 4.63 % 4.0 % 3.4 % 4.1 % 4.9 % 3.9 % 4.9 % Service cost 4.83 % N/A 4.87 % 4.0 % N/A 4.1 % 4.9 % N/A 4.9 % Interest cost 3.86 % 3.04 % 3.9 % 4.0 % 3.4 % 4.1 % 4.9 % 3.9 % 4.9 % Expected long-term return on plan assets 7.0 % N/A N/A 7.5 % N/A N/A 7.5 % N/A N/A Rate of compensation increase 4.5 % N/A 4.5 % 4.5 % N/A 4.5 % 4.75 % N/A 4.75 % _____________________ (a) The Retirement Plan and the Excess Benefit Plan were remeasured on February 28, 2014 due to the above mentioned plan amendment. The discount rate used to remeasure the benefit obligation was 4.6% for the Retirement Plan and 4.5% for the Excess Benefit Plan, compared to 4.9% for both plans as of January 1, 2014 . All other assumptions remained consistent with assumptions used at January 1, 2014 .
Other Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Schedule of Net Funded Status	The following table contains a reconciliation of the change in the benefit obligation, the fair value of plan assets, and the funded status of the plan (in thousands): December 31, 2016 2015 Change in benefit obligation: Benefit obligation at end of prior year $ 92,643 $ 100,700 Service cost 2,769 3,454 Interest cost 3,167 4,035 Actuarial loss (gain) 10,751 (11,423 ) Amendment (a) (b) (32,697 ) (824 ) Benefits paid (4,428 ) (4,544 ) Retiree contributions 1,310 1,245 Benefit obligation at end of year 73,515 92,643 Change in plan assets: Fair value of plan assets at end of prior year 38,090 41,358 Actual return (loss) on plan assets 2,443 (469 ) Employer contribution 1,700 500 Benefits paid (4,428 ) (4,544 ) Retiree contributions 1,310 1,245 Fair value of plan assets at end of year 39,115 38,090 Funded status at end of year $ (34,400 ) $ (54,553 ) _____________________ (a) During October 2016, the Company approved and communicated a plan amendment that resulted in a remeasurement of the Company's Other Post-retirement Benefit Plan. Effective January 1, 2017, retirees and dependents that are less than 65 years of age are offered a choice between a $1,000 and $2,250 deductible plan. Additionally, retirees and dependents that are 65 years of age or greater were covered by a fully insured Medicare advantage plan. (b) Amendment relates to modification of the Company's Other Post-retirement Benefit Plan which increased mail order co-payments for post age 65. The amendment was approved in 2015 and became effective January 1, 2016 .
Schedule of Amounts Recognized in Balance Sheet	Amounts recognized in the Company's balance sheets consist of the following (in thousands): December 31, 2016 2015 Current liabilities $ — $ — Noncurrent liabilities (34,400 ) (54,553 ) Total $ (34,400 ) $ (54,553 )
Schedule of Amount Recognized in Accumulated Other Comprehensive Income (Loss)	Pre-tax amounts recognized in accumulated other comprehensive income consist of the following (in thousands): December 31, 2016 2015 Net gain $ (26,285 ) $ (38,802 ) Prior service benefit (41,009 ) (12,213 ) Total $ (67,294 ) $ (51,015 )
Schedule of Net Periodic Benefit Costs	Net periodic benefit cost is made up of the components listed below (in thousands): Years Ended December 31, 2016 2015 2014 Service cost $ 2,769 $ 3,454 $ 2,845 Interest cost 3,167 4,035 4,463 Expected return on plan assets (1,835 ) (2,070 ) (2,116 ) Amortization of: Prior service benefit (3,901 ) (3,068 ) (4,753 ) Net gain (2,374 ) (2,025 ) (2,671 ) Net periodic benefit cost $ (2,174 ) $ 326 $ (2,232 )
Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income (Loss)	The changes in benefit obligations recognized in other comprehensive income are presented below (in thousands): Years Ended December 31, 2016 2015 2014 Net (gain) loss $ 10,143 $ (8,884 ) $ 3,496 Prior service benefit (32,697 ) (824 ) — Amortization of: Prior service benefit 3,901 3,068 4,753 Net gain 2,374 2,025 2,671 Total recognized in other comprehensive income $ (16,279 ) $ (4,615 ) $ 10,920
Schedule of Recognized Net Periodic Benefit Obligation and Other Comprehensive Income	The total amount recognized in net periodic benefit cost and other comprehensive income are presented below (in thousands): Years Ended December 31, 2016 2015 2014 Total recognized in net periodic benefit cost and other comprehensive income $ (18,453 ) $ (4,289 ) $ 8,688
Schedule of Allocation of Plan Assets	The Company’s target allocations for the plan’s assets are presented below: December 31, 2016 Equity securities 65 % Fixed income 30 % Alternative investments 5 % Total 100 %
Fair Value, Measurement Inputs, Disclosure	The fair value of the Company’s Other Post-retirement Benefits Plan assets at December 31, 2016 and 2015 , and the level within the three levels of the fair value hierarchy defined by the FASB guidance on fair value measurements are presented in the table below (in thousands): Description of Securities Fair Value as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Institutional Funds (a) Equity funds $ 26,133 $ 26,133 $ — $ — Fixed income funds 11,671 11,671 — — Total Institutional Funds 37,804 37,804 — — Limited Partnership Interest in Real Estate (b) (c) 1,311 Total Plan Investments $ 39,115 $ 37,804 $ — $ — 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) Institutional Funds (a) Equity funds $ 24,881 $ 24,881 $ — $ — Fixed income funds 11,599 11,599 — — Total Institutional Funds 36,480 36,480 — — Limited Partnership Interest in Real Estate (b) (c) 1,610 Total Plan Investments $ 38,090 $ 36,480 $ — $ — ___________________ (a) The institutional funds are invested in equity or fixed income securities, or a combination thereof. The investment objective of each fund is to produce returns in excess of, or commensurate with, its predefined index. (b) This investment is a commercial real estate partnership that purchases land, develops limited infrastructure, and sells it for commercial development. The Company was restricted from selling its partnership interest during the life of the partnership, which spanned 7 years. Return of investment is realized as land is sold. The fair value of the limited partnership interest in real estate is based on the NAV of the partnership which reflects the appraised value of the land. The partnership term expired on June 30, 2016 . Upon expiration, dissolution of the partnership commenced and, as a result, the general partner of the partnership is attempting to sell the remaining inventory as soon as possible at the highest pricing possible. (c) In the first quarter of 2016, the Company implemented ASU 2015-07, Fair Value Measurement (Topic 820) which eliminates the requirement to categorize investments in the fair value hierarchy if the fair value is measured at NAV per share (or its equivalent) using the practical expedient in the FASB’s fair value measurement gui dance . The fair value amounts presented in the table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the statement of financial position. ASU 2015-07 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years.
Changes in Fair Value of Investments in Real Estate	The table below reflects the changes in the fair value of the investments in real estate during the period (in thousands): Fair Value of Investments in Real Estate Balance at December 31, 2014 $ 1,640 Unrealized loss in fair value (30 ) Balance at December 31, 2015 1,610 Sale of land (145 ) Unrealized loss in fair value (154 ) Balance at December 31, 2016 $ 1,311
Schedule of Expected Benefit Payments	The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid (in thousands): 2017 $ 2,622 2018 2,880 2019 3,057 2020 3,320 2021 3,510 2022-2026 20,084
Other Postretirement Benefit Plan | Accrued Postretirement Benefit
Defined Benefit Plan Disclosure [Line Items]
Schedule of Assumptions Used	The following are the weighted-average actuarial assumptions used to determine the accrued post-retirement benefit obligations: December 31, 2016 2015 Discount rate at end of year 4.36 % 4.59 % Health care cost trend rates: Initial Pre-65 medical 6.50 % 7.00 % Post-65 medical 4.50 % 7.00 % Pre-65 drug 7.50 % 7.00 % Post-65 drug 10.50 % 7.00 % Ultimate 4.50 % 4.50 % Year ultimate reached (a) 2026 2026 _____________________ (a) Pre-65 medical reaches the ultimate trend rate in 2025. Additionally, the Post-65 medical trend is assumed to be 4.50% for all years into the future.
Other Postretirement Benefit Plan | Net Periodic Benefit Costs
Defined Benefit Plan Disclosure [Line Items]
Schedule of Assumptions Used	The following are the weighted-average actuarial assumptions used to determine the net periodic benefit cost for the twelve months ended December 31 : 2016 (a) 2015 2014 Discount rate: January 1 - September 30 October 1 - December 31 Benefit obligation 4.59 % 3.75 % 4.1 % 4.9 % Service cost 4.91 % 4.03 % 4.1 % 4.9 % Interest cost 3.86 % 3.15 % 4.1 % 4.9 % Expected long-term return on plan assets 4.875% 5.2 % 5.2 % Health care cost trend rates: Initial 7.00% 7.25 % 7.5 % Ultimate 4.5% 4.5 % 4.5 % Year ultimate reached 2026 2026 2026 _____________________ (a) The actuarial assumptions are evaluated by the Company at each measurement date. The Other Post-retirement Benefits Plan was remeasured at October 1, 2016 due to a plan amendment.

Financial Instruments And Inv39

Financial Instruments And Investments (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Values Of Long-Term Debt And Short-Term Borrowings Under the RCF	The fair values of the Company's long-term debt and short-term borrowings under the RCF are based on estimated market prices for similar issues and are presented below (in thousands): December 31, 2016 2015 Carrying Amount (1) Estimated Fair Value Carrying Amount (1) Estimated Fair Value Pollution Control Bonds $ 190,775 $ 206,818 $ 190,499 $ 212,624 Senior Notes 993,086 1,112,285 837,475 829,864 RGRT Senior Notes (2) 94,795 98,855 94,686 100,345 RCF (2) 81,574 81,574 141,738 141,738 Total $ 1,360,230 $ 1,499,532 $ 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 December 31, 2016 and December 31, 2015 , is funded through the $95 million RGRT Senior Notes and $37.6 million and $33.7 million , respectively under the RCF. As of December 31, 2016 , $44.0 million was outstanding under the RCF for working capital or general corporate purposes. As of December 31, 2015 , $108.0 million amount 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 period reflecting current 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): December 31, 2016 Less than 12 Months 12 Months or Longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Description of Securities (1) : Federal Agency Mortgage Backed Securities $ 11,582 $ (239 ) $ 436 $ (22 ) $ 12,018 $ (261 ) U.S. Government Bonds 31,655 (762 ) 17,976 (835 ) 49,631 (1,597 ) Municipal Obligations 9,596 (394 ) 4,067 (372 ) 13,663 (766 ) Corporate Obligations 7,971 (172 ) 2,092 (172 ) 10,063 (344 ) Total Debt Securities 60,804 (1,567 ) 24,571 (1,401 ) 85,375 (2,968 ) Common Stock 2,760 (167 ) — — 2,760 (167 ) Institutional Funds-International Equity 22,945 (110 ) — — 22,945 (110 ) Total Temporarily Impaired Securities $ 86,509 $ (1,844 ) $ 24,571 $ (1,401 ) $ 111,080 $ (3,245 ) ____________________ (1) Includes approximately 152 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 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 approximately 133 securities.
Unrealized Holding Losses Included In Pre-Tax Income	For the twelve months ended December 31, 2016 , 2015 , and 2014 , the Company recognized other than temporary impairment losses on its available-for-sale securities as follows (in thousands): 2016 2015 2014 Unrealized holding losses included in pre-tax income $ (352 ) $ (338 ) $ —
Marketable Securities Fair Value and Unrecognized Gross Unrealized Gain	The table below presents the unrecognized gross unrealized gains and the fair value of these securities, aggregated by investment category (in thousands): December 31, 2016 December 31, 2015 Fair Value Unrealized Gains Fair Value Unrealized Gains Description of Securities: Federal Agency Mortgage Backed Securities $ 7,430 $ 319 $ 9,589 $ 438 U.S. Government Bonds 12,237 138 12,033 136 Municipal Obligations 2,481 144 8,671 332 Corporate Obligations 12,350 655 10,110 368 Total Debt Securities 34,498 1,256 40,403 1,274 Common Stock 61,884 34,066 72,636 37,001 Equity Mutual Funds 42,244 3,345 18,853 91 Cash and Cash Equivalents 6,002 — 8,204 — Total $ 144,628 $ 38,667 $ 140,096 $ 38,366
Contractual Year For Maturity Of Available-For-Sale Securities	The contractual year for maturity for these available-for-sale securities as of December 31, 2016 is as follows (in thousands): Total 2017 2018 through 2022 through 2026 2027 and Beyond Municipal Debt Obligations $ 16,144 $ 990 $ 6,253 $ 8,139 $ 762 Corporate Debt Obligations 22,413 — 8,664 6,090 7,659 U.S. Government Bonds 61,868 14,272 22,495 14,786 10,315 Federal Agency Mortgage Backed Securities 19,448 — 5 390 19,053
Sale of Securities And The Related Effects On Pre-Tax Income	The proceeds from the sale of these securities during the twelve months ended December 31, 2016 , 2015 , and 2014 and the related effects on pre-tax income are as follows (in thousands): 2016 2015 2014 Proceeds from sales of available-for-sale securities $ 91,268 $ 102,567 $ 108,311 Gross realized gains included in pre-tax income $ 9,212 $ 12,379 $ 7,858 Gross realized losses included in pre-tax income (1,220 ) (927 ) (508 ) Gross unrealized losses included in pre-tax income (352 ) (338 ) — Net gains in pre-tax income $ 7,640 $ 11,114 $ 7,350 Net unrealized holding gains (losses) included in accumulated other comprehensive income $ 8,444 $ (2,906 ) $ 10,827 Net (gains) losses reclassified out of accumulated other comprehensive income (7,640 ) (11,114 ) (7,350 ) Net gains (losses) in other comprehensive income $ 804 $ (14,020 ) $ 3,477
Fair Value, Measurement Inputs, Disclosure	The fair value of the Company’s decommissioning trust funds and investments in debt securities at December 31, 2016 and 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 December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Trading Securities: Investments in Debt Securities $ 1,421 $ — $ — $ 1,421 Available for sale: U.S. Government Bonds $ 61,868 $ 61,868 $ — $ — Federal Agency Mortgage Backed Securities 19,448 — 19,448 — Municipal Obligations 16,144 — 16,144 — Corporate Obligations 22,413 — 22,413 — Subtotal, Debt Securities 119,873 61,868 58,005 — Common Stock 64,644 64,644 — — Equity Mutual Funds 42,244 42,244 — — Institutional Funds-International Equity 22,945 22,945 — — Cash and Cash Equivalents 6,002 6,002 — — Total available for sale $ 255,708 $ 197,703 $ 58,005 $ — 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 Obligations 24,345 — 24,345 — Corporate 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 $ —
Trading Securities (and Certain Trading Assets)	Below is a reconciliation of the beginning and ending balance of the fair value of the investment in debt securities (in thousands): 2016 2015 Balance at January 1 $ 1,543 $ 1,653 Net unrealized gains (losses) in fair value recognized in income (a) (122 ) (110 ) Balance at December 31 $ 1,421 $ 1,543 _____________________ (a) These amounts are reflected in the Company's statements of operations as investment and interest income.

Supplemental Statements of Ca40

Supplemental Statements of Cash Flows Disclosures (Tables)	12 Months Ended
	Dec. 31, 2016
Supplemental Cash Flow Information [Abstract]
Schedule of Cash Flow, Supplemental Disclosures	Years Ended December 31, 2016 2015 2014 (In thousands) Cash paid for: Interest on long-term debt and borrowing under the revolving credit facility $ 69,990 $ 62,297 $ 54,792 Income taxes, net of refund 2,328 1,000 6,876 Non-cash investing and financing activities: Sale of Interest in Four Corners Generating Station (a) 27,720 — — Changes in accrued plant additions 4,789 (6,660 ) 7,314 Grants of restricted shares of common stock 1,236 1,567 3,025 (a) The Company sold its interest in Four Corners for approximately $32.0 million based on the book value as defined in the Purchase and Sale Agreement. The sales price was adjusted downward by $7.0 million and $19.5 million to reflect APS's affiliate assumption of the Company's obligation to pay for future plant decommissioning and mine reclamation expense, respectively. The sales price was also adjusted downward by approximately $1.3 million for closing adjustments and other assets and liabilities assumed by APS's affiliate. At the closing of the sale, the Company received approximately $4.2 million in cash, subject to post-closing adjustments.

Selected Quarterly Financial 41

Selected Quarterly Financial Data (Unaudited) Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	The quarterly earnings per share amounts for a year will not add to the earnings per share for that year due to the weighting of shares used in calculating per share data. 2016 Quarters 2015 Quarters 4th 3rd (2) 2nd 1st 4th 3rd 2nd 1st (In thousands except for share data) Operating revenues (1) $ 188,037 $ 323,225 $ 217,865 $ 157,809 $ 176,902 $ 289,713 $ 219,508 $ 163,746 Operating income (loss) 20,470 129,857 44,697 (163 ) 8,312 88,047 41,872 7,960 Net income (loss) 5,656 74,636 22,284 (5,808 ) 648 56,740 21,072 3,458 Basic earnings per share: Net income (loss) 0.14 1.84 0.55 (0.14 ) 0.02 1.40 0.52 0.09 Diluted earnings per share: Net income (loss) 0.14 1.84 0.55 (0.14 ) 0.02 1.40 0.52 0.09 Dividends declared per share of common stock 0.310 0.310 0.310 0.295 0.295 0.295 0.295 0.280 ________________ (1) Operating revenues are seasonal in nature, with the peak sales periods generally occurring during the summer months. Comparisons among quarters of a year may not represent overall trends and changes in operations. (2) For financial reporting purposes, the Company deferred any recognition of the Company's request in its 2015 Texas Retail Rate Case until it received the PUCT Final Order on August 25, 2016. Accordingly, it reported in the third quarter of 2016 the cumulative effect of the PUCT Final Order which related back to January 12, 2016. See Part II, Item 8, Financial Statements and Supplementary Data, Note C.

Summary of Significant Accoun42

Summary of Significant Accounting Policies (General) (Details)	Dec. 31, 2016mi²
General [Abstract]
Area of Services, in Square Miles	10,000

Summary of Significant Accoun43

Summary of Significant Accounting Policies (Utility Plant) (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Significant Accounting Policies [Line Items]
Average composite depreciation rate	2.28%	2.64%	2.60%
AFUDC rate	6.43%	7.18%	8.15%
Minimum
Significant Accounting Policies [Line Items]
Public Utilities Property, Plant and Equipment, Useful Life	5 years
Maximum
Significant Accounting Policies [Line Items]
Public Utilities Property, Plant and Equipment, Useful Life	48 years

Summary of Significant Accoun44

Summary of Significant Accounting Policies (Revenues) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Accrued unbilled revenues	$ 21	$ 21.7

Summary of Significant Accoun45

Summary of Significant Accounting Policies (Allowance For Doubtful Accounts) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts Receivable, Net [Abstract]
Balance at beginning of year	$ 2,046	$ 2,253	$ 2,261
Additions:
Charged to costs and expense	2,427	2,057	2,755
Recovery of previous write-offs	1,395	1,613	1,516
Uncollectible receivables written off	3,712	3,877	4,279
Balance at end of year	$ 2,156	$ 2,046	$ 2,253

New Accounting Standards Narrat

New Accounting Standards Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jan. 01, 2017	Jan. 01, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in accumulated other comprehensive income	$ 7,116	$ 13,914
Increase in income tax expense	53,918	34,895	$ 41,088
Decrease in other comprehensive income	(6,798)	5,913	$ 10,613
Increase in operating loss carryforward deferred tax assets	60,749	$ 35,153
Potential Impact of Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in retained earnings					$ 28,800
Decrease in accumulated other comprehensive income					$ 28,800
Increase in investment income	1,200
Increase in income tax expense	200
Decrease in other comprehensive income	$ 1,000
Subsequent Event | Potential Impact of Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in retained earnings				$ 200
Increase in operating loss carryforward deferred tax assets				$ 200

Regulation (Narrative) (Details

Regulation (Narrative) (Details) $ in Thousands

Feb. 13, 2017USD ($)

Jan. 10, 2017

Jan. 09, 2017USD ($)

Oct. 28, 2016USD ($)

Sep. 27, 2016USD ($)

Aug. 25, 2016USD ($)

Jul. 06, 2016USD ($)

Jun. 08, 2016USD ($)

Apr. 29, 2016USD ($)

Mar. 24, 2016USD ($)

Nov. 05, 2015USD ($)

May 20, 2015

May 01, 2015USD ($)

Dec. 01, 2014USD ($)

Dec. 31, 2016USD ($)MW

Dec. 31, 2015USD ($)

Dec. 31, 2014USD ($)

Jan. 08, 2017USD ($)

Sep. 30, 2016USD ($)

Oct. 19, 2015USD ($)

Oct. 07, 2015USD ($)

Under-collection of fuel revenues

$ 11,123

$ 0

Over-collection of fuel revenues

255

4,023

Proceeds from issuance of senior notes

157,052

0

$ 149,468

Interest Payable, Current

$ 13,287

$ 12,649

Number of Presidential Permit(s)

2

Contract Termination Provision, Period

2 years

PUCT Docket No. 44633 | Fixed Fuel Factor

Increase (Decrease) in Fixed Fuel Factor, Percentage

(24.00%)

PUCT Docket No. 46308

Reconcilable Fuel Expense

$ 436,600

Fuel Reconciliation Period

36 months

NMPRC Case No. 15-00127-UT

Fuel Reconciliation Period

24 months

Four Corners Generating Station

Closing Date For Sale

Jul. 6, 2016

Mine Reclamation and Closing Liability, Noncurrent

$ 19,500

PUCT

Period To Relate Back New Rates

155 days

Public Utilities Requested Performance Incentive Bonus Related To Energy Efficiency Program

$ 700

$ 1,000

Public Utilities Approved Performance Incentive Bonus Related To Energy Efficiency Program

$ 500

$ 1,000

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

$ 200

Fuel Over And Under Materiality Threshold Percentage

4.00%

Under-collection of fuel revenues

$ 11,100

Reconcilable Fuel Expense

$ 114,400

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 | Four Corners Generating Station

Purchase and Sale Agreement, Execution Date

Feb. 17, 2015

PUCT | Minimum

Fixed Fuel Factor Revision Period, in Months

4 months

PUCT | Maximum

Surcharge Or Refund Period

18 months

PUCT | Public Utilities, Regulatory Rate Making Impact

Recovery of Rate Case Expenses, Amount

$ 3,100

Period To Relate Back New Rates

80 days

PUCT | Four Corners Generating Station

Closing Date For Sale

Jul. 6, 2016

Mine Reclamation and Closing Liability, Noncurrent

$ 7,300

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

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 3,700

Regulatory Current Asset, End Date for Recovery

Jul. 12, 2017

NMPRC

Reconcilable Fuel Expense

$ 114,600

Fuel Reconciliation Period

24 months

Over-collection of fuel revenues

$ 200

Debt Instrument, Face Amount

$ 310,000

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 | Four Corners Generating Station

Purchase and Sale Agreement, Execution Date

Feb. 17, 2015

NMPRC | Holloman

Electric capacity | MW

5

NMPRC | Public Utilities, Regulatory Rate Making Impact

Public Utilities, Approved Return on Equity, Percentage

9.48%

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

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 600

NMPRC | Public Utilities, Regulatory Rate Making Impact | Service cost

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 500

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 For Sale

Jul. 6, 2016

Jointly Owned Utility Plant, Entire Ownership of Proportionate Interest, Percentage

100.00%

Subsequent Event

Line of Credit renewal term, year

1 year

Line of Credit Facility, Expiration Date

Jan. 14, 2021

Subsequent Event | PUCT Docket No. 46610 | Fixed Fuel Factor

Increase (Decrease) in Fixed Fuel Factor, Percentage

28.80%

Subsequent Event | PUCT | Non-Fuel Base Rate

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 42,500

Subsequent Event | FERC

Line of Credit renewal term, year

1 year

Line of Credit Facility, Expiration Date

Jan. 14, 2021

RGRT | NMPRC

Debt Instrument, Face Amount

$ 65,000

RGRT | FERC

Debt Instrument, Face Amount

$ 65,000

Revolving Credit Facility Expiring January 2020 | Subsequent Event

Line of Credit Facility, Maximum Borrowing Capacity

$ 400,000

Line of Credit renewal term, year

1 year

Line of Credit Facility, Expiration Date

Jan. 14, 2020

Line of Credit Facility, Increase (Decrease), Net

$ 50,000

Line of Credit Facility, Current Borrowing Capacity

350,000

Line of Credit Facility, Remaining Borrowing Capacity

50,000

Revolving Credit Facility Expiring January 2020 | Subsequent Event | FERC

Line of Credit Facility, Maximum Borrowing Capacity

$ 400,000

Line of Credit renewal term, year

1 year

Line of Credit Facility, Expiration Date

Jan. 14, 2020

Line of Credit Facility, Increase (Decrease), Net

$ 50,000

Line of Credit Facility, Current Borrowing Capacity

350,000

Line of Credit Facility, Remaining Borrowing Capacity

50,000

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

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, Combined, Due 2044 | NMPRC

Debt Instrument, Face Amount

$ 300,000

Letter of Credit | Revolving Credit Facility Expiring January 2020 | Subsequent Event | FERC | Maximum

Line of Credit Facility, Current Borrowing Capacity

$ 50,000

$ 350,000

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

Regulatory Assets and Liabili48

Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets		$ 118,861	$ 115,127
Total regulatory liabilities		18,435	24,303
Regulatory tax assets or liabilities
Regulatory Assets and Liabilities [Line Items]
Total regulatory liabilities	[1],[2]	10,648	17,266
Accumulated deferred investment tax credit
Regulatory Assets and Liabilities [Line Items]
Total regulatory liabilities	[1],[3]	3,328	4,011
Texas energy efficiency
Regulatory Assets and Liabilities [Line Items]
Total regulatory liabilities	[4]	1,288	0
New Mexico energy efficiency
Regulatory Assets and Liabilities [Line Items]
Total regulatory liabilities	[4]	2,159	2,238
Texas military base discount and recovery factor
Regulatory Assets and Liabilities [Line Items]
Total regulatory liabilities	[5]	$ 184	788
New Mexico gain on sale of assets
Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Amortization Period		3 years
Total regulatory liabilities	[6]	$ 828	0
Regulatory tax assets or liabilities
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	[1],[2]	66,670	69,359
Loss on reacquired debt
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	[7]	15,780	16,632
Final coal reclamation
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	[8],[9]	9,581	9,520
Nuclear fuel postload daily financing charge
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	[8]	3,831	4,195
Unrecovered issuance costs due to reissuance of PCBs
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	[7]	794	827
Texas energy efficiency
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	[4]	0	25
Texas 2015 rate case costs
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets		2,670	1,882
Texas 2017 rate case costs
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	[10]	246	0
Texas relate back surcharge
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	[11]	6,455	0
New Mexico renewable energy credits and related costs
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	[12]	6,937	6,397
New Mexico 2010 FPPCAC audit
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets		398	434
New Mexico Palo Verde deferred depreciation
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	[1]	4,415	4,568
New Mexico 2015 rate case costs
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets		1,074	1,288
New Mexico 2017 rate case costs
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	[10]	$ 10	$ 0
[1]	The amortization periods for these assets and liabilities are based upon the life of the associated assets or liabilities.
[2]	We do not earn a return on these items since the related accumulated deferred income tax assets and liabilities offset.
[3]	This item is excluded from rate base.
[4]	This item is recovered or credited through a recovery factor that is set annually.
[5]	This item represents the net asset/net liability related to the military discount which is recovered from non-military customers through a recovery factor that is set annually.
[6]	This item relates to the gains on the sales of assets the Company shares with its New Mexico customers over a three year period.
[7]	This item is recovered as a component of the weighted cost of debt and amortized over the life of the related debt issuance.
[8]	This item is recovered through fuel recovery mechanisms established by tariffs.
[9]	This item relates to coal reclamation costs associated with Four Corners. See Part II, Item 8, Financial Statements and Supplementary Data, Note C.
[10]	Amortization period is anticipated to be established in next general rate case.
[11]	This item relates to the recovery of revenues through a separate surcharge beginning October 1, 2016 and ending September 30, 2017. See Part II, Item 8, Financial Statements and Supplementary Data, Note C.
[12]	This item relates to renewable energy credits and procurement plan costs, components approved for recovery in the New Mexico 2015 rate case.

Utility Plant, Palo Verde and49

Utility Plant, Palo Verde and Other Jointly-Owned Utility Plant (Depreciable Assets By Each Major Class) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	$ 3,791,566	$ 3,616,301
Accumulated Depreciation	(1,244,332)	(1,329,843)
Property, Plant and Equipment, Net	2,547,234	$ 2,286,458
Intangible
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	84,342
Accumulated Depreciation	(55,464)
Property, Plant and Equipment, Net	28,878
Nuclear production | Energy Equipment
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	948,382
Accumulated Depreciation	(320,000)
Property, Plant and Equipment, Net	628,382
Steam and other | Energy Equipment
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	926,419
Accumulated Depreciation	(186,539)
Property, Plant and Equipment, Net	739,880
Total production | Energy Equipment
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	1,874,801
Accumulated Depreciation	(506,539)
Property, Plant and Equipment, Net	1,368,262
Transmission | Energy Equipment
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	498,660
Accumulated Depreciation	(259,488)
Property, Plant and Equipment, Net	239,172
Distribution | Energy Equipment
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	1,127,897
Accumulated Depreciation	(365,601)
Property, Plant and Equipment, Net	762,296
General | Energy Equipment
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	205,866
Accumulated Depreciation	(57,240)
Property, Plant and Equipment, Net	$ 148,626

Utility Plant, Palo Verde and50

Utility Plant, Palo Verde and Other Jointly-Owned Utility Plant (Amortization of Intangible Plant Assets - Software) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Number of years amortization expense prior reporting year		3 years
Number of years amortization expense after reporting year		5 years
Intangible Plant Software
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Decrease in depreciation expense	$ 1,800
Finite-Lived Intangible Assets, Amortization Expense		$ 5,302	$ 6,482	$ 8,051
Future Amortization Expense, 2017 (estimated)		5,148
Future Amortization Expense, 2018 (estimated)		4,631
Future Amortization Expense, 2019 (estimated)		4,242
Future Amortization Expense, 2020 (estimated)		3,808
Future Amortization Expense, 2021 (estimated)		$ 3,227
Intangible Plant Software | Minimum
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Useful Life		3 years
Intangible Plant Software | Maximum
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Useful Life		15 years

Utility Plant, Palo Verde and51

Utility Plant, Palo Verde and Other Jointly-Owned Utility Plant (Summary of Jointly Owned Utility Plants) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)utilityplantunit	Jul. 06, 2016	Dec. 31, 2015USD ($)
Palo Verde Generating Station
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	15.80%
Jointly Owned Utility Plant, Number of Units | utilityplantunit	3
Palo Verde Participants
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Plant, Number of Participants	6
Four Corners Generating Station
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share		7.00%
Other Jointly Owned Utlity Plant
Jointly Owned Utility Plant Interests [Line Items]
Electric plant in service	$ 67,621		$ 229,627
Accumulated depreciation	(44,377)		(181,886)
Construction work in progress	1,895		9,528
Total	25,139		57,269
Palo Verde | Jointly Owned Nuclear Power Plant
Jointly Owned Utility Plant Interests [Line Items]
Electric plant in service	948,382		917,483
Accumulated depreciation	(320,000)		(304,060)
Construction work in progress	50,598		48,938
Total	$ 678,980		$ 662,361

Utility Plant, Palo Verde and52

Utility Plant, Palo Verde and Other Jointly-Owned Utility Plant (Narrative) (Details) $ in Thousands

Oct. 31, 2016USD ($)

Jul. 06, 2016USD ($)

Mar. 31, 2016USD ($)

Nov. 02, 2015USD ($)

Jun. 01, 2015USD ($)

Oct. 31, 2014USD ($)

Oct. 08, 2014USD ($)

Aug. 18, 2014USD ($)

Mar. 31, 2013USD ($)

Dec. 19, 2012

Dec. 31, 2016USD ($)utilityplantunit

Dec. 31, 2015USD ($)

Dec. 31, 2014USD ($)

Dec. 31, 2013USD ($)

Apr. 21, 2011

Jointly Owned Utility Plant Interests [Line Items]

Proceeds from sale of property, plant, and equipment

$ 4,841

$ 721

$ 2,395

Decommissioning Fund Investments

$ 255,708

239,035

Third Party Decommission Cost Estimates Study Period, in Years

3 years

Estimated Decommissioning Costs

$ 380,700

Decommission cost increase

$ 23,300

Asset Retirement Obligation, Revision of Estimate

$ 0

0

3,561

Required period in years participants need a new decommissioning study

3 years

Retrospective Premium Adjustments Due to Nuclear Facility Losses

$ 12,900

Asset Retirement Obligation

81,800

81,621

74,577

$ 65,214

Refund passed through to customers

$ (14,891)

$ 13,344

$ (3,121)

Four Corners Generating Station

Jointly Owned Utility Plant Interests [Line Items]

Proceeds from sale of property, plant, and equipment

$ 4,200

Jointly Owned Utility Plant, Proportionate Ownership Share

7.00%

Property, Plant and Equipment, Disposals

$ 32,000

Disposal Date

Jul. 6, 2016

Asset Retirement Obligation

$ 7,000

Mine Reclamation and Closing Liability, Noncurrent

19,500

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

$ 1,300

Palo Verde Generating Station

Jointly Owned Utility Plant Interests [Line Items]

Number Of Power Generation Units

3

Number of Units With Renewed Operating Licenses

3

Asset Retirement Obligation, Revision of Estimate

$ 1,900

Maximum Assesment Per Reactor Nuclear Energy Incident

$ 60,400

Maximum Assesment Per Reactor Nuclear Energy Incident Annual Limit

$ 9,000

Jointly Owned Utility Plant, Proportionate Ownership Share

15.80%

Jointly Owned Utility Plant, Number of Units | utilityplantunit

3

Palo Verde Participants

Jointly Owned Utility Plant Interests [Line Items]

Nuclear Energy Hazards Full Limit Of Liability Under Federal Law

$ 13,400,000

Nuclear Energy Hazards Potential Liability

450,000

Maximum Assesment Per Reactor Nuclear Energy Incident

127,300

Maximum Assesment Per Reactor Nuclear Energy Incident Annual Limit

19,000

Aggregate Amount of Insurance for Decontamination and Property Damage

2,750,000

Suit Against Department of Energy for Spent Fuel

Jointly Owned Utility Plant Interests [Line Items]

Settlement Agreement, Counterparty's Name

United States Department of Energy

Lawsuit Filing Date

October 31, 2016

November 2, 2015

October 31, 2014

December 19, 2012

Loss Contingency, 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 Agreement Award Received, Date

Jun. 1, 2015

Oct. 8, 2014

Settlement, Amount

$ 1,900

$ 6,600

$ 9,100

Litigation, Claim Amount

$ 1,800

Refund passed through to customers

$ 1,600

$ 5,800

$ 7,900

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

Jointly Owned Utility Plant Interests [Line Items]

Settlement, Amount

$ 11,300

$ 12,000

$ 42,000

$ 57,400

Minimum | Suit Against Department of Energy for Spent Fuel

Jointly Owned Utility Plant Interests [Line Items]

Litigation, Period Covered

July 1, 2015

Jul. 1, 2014

Jul. 1, 2011

Jan. 1, 2007

Maximum | Suit Against Department of Energy for Spent Fuel

Jointly Owned Utility Plant Interests [Line Items]

Litigation, Period Covered

June 30, 2016

Jun. 30, 2015

Jun. 30, 2014

Jun. 30, 2011

Limited amount of coverage | Palo Verde Participants

Jointly Owned Utility Plant Interests [Line Items]

Aggregate Amount of Insurance for Decontamination and Property Damage

$ 2,250,000

PUCT | Four Corners Generating Station

Jointly Owned Utility Plant Interests [Line Items]

Disposal Date

Jul. 6, 2016

Mine Reclamation and Closing Liability, Noncurrent

$ 7,300

Public Utilities, Regulatory Rate Making Impact

Jointly Owned Utility Plant Interests [Line Items]

Decrease in depreciation expense

$ 10,900

Accounting for Asset Retireme53

Accounting for Asset Retirement Obligations (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Accounting For Asset Retirement Obligations [Line Items]
Number of External Trust Funds with Independent Trustee with Legal Restrictions To Settling ARO	6
Decommissioning Fund Investments	$ 255,708	$ 239,035

Accounting for Asset Retireme54

Accounting for Asset Retirement Obligations (Changes in Estimated Probabilities Assumptions) (Details)	12 Months Ended
	Dec. 31, 2016
Original ARO Liability [Member]
Accounting For Asset Retirement Obligations [Line Items]
Escalation Rate	3.60%
Credit-Risk Adjusted Discount Rate	9.50%
Incremental ARO Liability [Member]
Accounting For Asset Retirement Obligations [Line Items]
Escalation Rate	3.60%
Credit-Risk Adjusted Discount Rate	6.20%

Accounting for Asset Retireme55

Accounting for Asset Retirement Obligations (Schedule of Asset Retirement Obligations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis
ARO liability at beginning of year	$ 81,621	$ 74,577	$ 65,214
Liabilities incurred	0	189	0
Liabilities settled	(6,993)	0	0
Revisions to estimate	0	0	3,561
Accretion expense	7,172	6,855	5,802
ARO liability at end of year	$ 81,800	$ 81,621	$ 74,577

Common Stock (Details)

Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands

Mar. 31, 2017

Mar. 17, 2017

Jan. 26, 2017

Dec. 30, 2016

Dec. 31, 2016

Sep. 30, 2016

[1]

Jun. 30, 2016

Mar. 31, 2016

Dec. 31, 2015

Sep. 30, 2015

Jun. 30, 2015

Mar. 31, 2015

Dec. 31, 2016

Dec. 31, 2015

Dec. 31, 2014

May 29, 2014

Common Stock [Line Items]

Dividends, Common Stock, Cash

$ 12,600

$ 49,603

$ 47,059

$ 44,556

Common Stock, Dividends, Per Share, Declared

$ 0.310

$ 0.310

$ 0.310

$ 0.295

$ 0.295

$ 0.295

$ 0.295

$ 0.280

$ 1.225

$ 1.165

$ 1.105

Common Stock, Par or Stated Value Per Share

$ 1

$ 1

$ 1

$ 1

Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized

1,700,000

Restricted Stock | Minimum

Common Stock [Line Items]

Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period

1 year

Restricted Stock | Maximum

Common Stock [Line Items]

Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period

3 years

Scenario, Forecast

Common Stock [Line Items]

Dividends Payable, Date to be Paid

Mar. 31, 2017

Dividends Payable, Date of Record

Mar. 17, 2017

Subsequent Event

Common Stock [Line Items]

Dividends Payable, Date Declared

Jan. 26, 2017

Common Stock, Dividends, Per Share, Declared

$ 0.31

[1]

For financial reporting purposes, the Company deferred any recognition of the Company's request in its 2015 Texas Retail Rate Case until it received the PUCT Final Order on August 25, 2016. Accordingly, it reported in the third quarter of 2016 the cumulative effect of the PUCT Final Order which related back to January 12, 2016. See Part II, Item 8, Financial Statements and Supplementary Data, Note C.

Common Stock (Schedule of Restr

Common Stock (Schedule of Restricted Stock Tax Expense and Deferred Tax) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Capitalized costs related to restricted stock award expense		$ 300	$ 300	$ 300
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense	[1]	2,594	2,755	3,471
Deferred tax benefit		908	964	1,215
Current tax benefit recognized		$ 183	$ 43	$ 39
[1]	Any capitalized costs related to these expenses is less than $0.3 million for all years.

Common Stock (Vested Restricted

Common Stock (Vested Restricted Stock Aggregate Intrinsic Value And Grant Date Fair Value) (Details) - Restricted Stock - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares vested - aggregated intrinsic value	$ 2,515	$ 3,451	$ 3,441
Fair value at grant date	$ 1,993	$ 3,327	$ 3,330

Common Stock (Schedule of Res59

Common Stock (Schedule of Restricted Stock) (Details) - USD ($) $ / shares in Units, $ in Thousands		May 29, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Share Price		$ 37.81
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Share based compensation, outstanding at beginning of period, in shares		13,863	91,210
Shares awards, number of shares awarded in period		13,863	74,181
Total vested, in shares		(13,863)	(55,503)
Total forfeitures, in shares		(13,863)	(495)
Share based compensation, outstanding at end of period, in shares			109,393	91,210
Shares outstanding, weighted average grant date fair value,beginning of period			$ 36.61
Weighted average fair value per share			40.95	$ 37.17	$ 36.95
Weighted average fair value vested			35.91
Weighted average fair value forfeitures			36.88
Shares outstanding, weighted average grant date fair value, end of period			$ 39.90	$ 36.61
Unrecognized Compensation Expense at end of period	[1]		$ 1,767
Aggregated intrinsic value for shares outstanding at end of period			$ 5,087
Unrecognized compensation expense, period for recognition			1 year
[1]	The unrecognized compensation expense is expected to be recognized over the weighted average remaining contractual term of the outstanding restricted stock of approximately one year.

Common Stock (Weighted Average

Common Stock (Weighted Average Fair Value Per Share) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value per share	$ 40.95	$ 37.17	$ 36.95

Common Stock (Performance Share

Common Stock (Performance Shares) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
The Number of Simulations on Fair Value of Average Payout	1,000,000
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Shares Payout Level	0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Shares Payout Level	200.00%
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment award on performance, performance evaluation period	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Method Used	Monte Carlo simulation
Performance Shares Payout Level	100.00%
Performance Shares | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance shares vested - Performance Shares Awarded | shares	206,898
January 25, 2017 | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance shares vested - Payout Ratio	32.00%
Performance shares vested - Performance Shares Awarded | shares	11,314
Performance shares vested - Compensation Costs Expensed	$ 932
Performance shares vested - aggregated intrinsic value	$ 512
January 27, 2016 | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance shares vested - Payout Ratio	0.00%
Performance shares vested - Performance Shares Awarded | shares	0
Performance shares vested - Compensation Costs Expensed	$ 851
Performance shares vested - aggregated intrinsic value	$ 0
February 20, 2015 | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance shares vested - Payout Ratio	0.00%
Performance shares vested - Performance Shares Awarded | shares	0
Performance shares vested - Compensation Costs Expensed	$ 1,502
Performance shares vested - aggregated intrinsic value	$ 0
February 18, 2014 | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance shares vested - Payout Ratio	0.00%
Performance shares vested - Performance Shares Awarded | shares	0
Performance shares vested - Compensation Costs Expensed	$ 954
Performance shares vested - aggregated intrinsic value	$ 0

Common Stock (Outstanding Perfo

Common Stock (Outstanding Performance Share Awards) (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Shares Payout Level		100.00%
Share based compensation, outstanding at beginning of period, in shares	[1]	130,136
Shares awards, number of shares awarded in period		60,835
Performance shares awards, number of shares expired in period		(24,527)
Share based compensation, outstanding at end of period, in shares	[1]	166,444	130,136
Shares outstanding, weighted average grant date fair value,beginning of period	[1]	$ 32.72
Performance shares awards, Weighted Average Grant Date Fair Value		38.11	$ 35.72	$ 26.36
Performance shares expired, weighted average grant date fair value		34.69
Shares outstanding, weighted average grant date fair value, end of period	[1]	$ 34.40	$ 32.72
Unrecognized Compensation Expense at end of period	[1],[2]	$ 2,189
Aggregated intrinsic value for shares outstanding at end of period	[1]	$ 7,740
Unrecognized compensation expense, period for recognition		1 year
Restricted Stock with a Performance Condition [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares awards, number of shares awarded in period			27,624
Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period			5 years
[1]	On December 15, 2015, the Company issued a stock based retention grant to the Chief Executive Officer (CEO) of 27,624 shares in accordance with the Amended and Restated 2007 LTIP that is eligible for vesting based on the achievement of certain performance conditions and a five year service period, as stated in the CEO's employment agreement. The performance condition was met as of November 2016 as determined by the Compensation Committee, and has been included in the beginning and ending balance in the table above.
[2]	The unrecognized compensation expense is expected to be recognized over the weighted average remaining contractual term of the awards of approximately one year, except for the CEO retention grant.

Common Stock (Performance Sha63

Common Stock (Performance Share Summary) (Details) - Performance Shares - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average per share grant date fair value per share of performance shares awarded		$ 38.11	$ 35.72	$ 26.36
Compensation expense	[1],[2]	$ 1,655	$ 1,042	$ 1,181
Deferred tax benefit related to compensation expense	[1]	$ 579	$ 365	$ 413
[1]	Includes CEO retention grant.
[2]	Includes adjustments for estimated forfeitures.

Common Stock (Common Stock Repu

Common Stock (Common Stock Repurchase Program) (Details) $ in Thousands	12 Months Ended	216 Months Ended
	Dec. 31, 2016shares	Dec. 31, 2016USD ($)shares
Equity, Class of Treasury Stock [Line Items]
Shares repurchased	0	25,406,184	[1],[2]
Cost, including commission | $		$ 423,647	[1]
Total remaining shares available for repurchase at December 31, 2016	393,816	393,816
Treasury shares acquired outside of repurchase programs		86,735
Stock Issued During Period, Shares, Treasury Stock Reissued	188,005
[1]	Represents repurchased shares and cost since inception of the stock repurchase program in 1999.
[2]	Shares repurchased does not include 86,735 treasury shares related to employee compensation arrangements outside of the Company's repurchase programs. Beginning in 2015, shares of the Company's common stock issued for employee benefit and stock incentive plans have been issued from the shares repurchased and held in treasury stock. The Company awarded 188,005 shares out of treasury stock during 2016.

Common Stock (Basic and Diluted

Common Stock (Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	[1]	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock Disclosures [Abstract]
Basic number of common shares outstanding										40,350,688	40,274,986	40,190,991
Dilutive effect of unvested performance awards										57,345	33,576	20,726
Diluted number of common shares outstanding										40,408,033	40,308,562	40,211,717
Net income	$ 5,656	$ 74,636		$ 22,284	$ (5,808)	$ 648	$ 56,740	$ 21,072	$ 3,458	$ 96,768	$ 81,918	$ 91,428
Income allocated to participating restricted stock										(321)	(243)	(301)
Net income available to common shareholders basic										96,447	81,675	91,127
Income reallocated to participating restricted stock										(321)	(243)	(301)
Net income available to common shareholders diluted										$ 96,447	$ 81,675	$ 91,127
Earnings Per Share, Basic, Distributed										$ 1.225	$ 1.165	$ 1.105
Earnings Per Share, Basic, Undistributed										1.165	0.865	1.165
Basic net income per common share	$ 0.14	$ 1.84		$ 0.55	$ (0.14)	$ 0.02	$ 1.40	$ 0.52	$ 0.09	2.390	2.030	2.270
Earnings Per Share, Diluted, Distributed										1.225	1.165	1.105
Earnings Per Share, Diluted, Undistributed										1.165	0.865	1.165
Diluted net income per common share	$ 0.14	$ 1.84		$ 0.55	$ (0.14)	$ 0.02	$ 1.40	$ 0.52	$ 0.09	$ 2.390	$ 2.030	$ 2.270
[1]	For financial reporting purposes, the Company deferred any recognition of the Company's request in its 2015 Texas Retail Rate Case until it received the PUCT Final Order on August 25, 2016. Accordingly, it reported in the third quarter of 2016 the cumulative effect of the PUCT Final Order which related back to January 12, 2016. See Part II, Item 8, Financial Statements and Supplementary Data, Note C.

Common Stock (Antidilutive Shar

Common Stock (Antidilutive Shares) (Details) - shares		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restricted Stock
Common Stock [Line Items]
Antidilutive Securities Excluded from Computation of Diluted Earnings Per Share, Amount		53,703	56,375	60,455
Performance Shares
Common Stock [Line Items]
Performance Shares Payout Level		100.00%	100.00%	100.00%
Antidilutive Securities Excluded from Computation of Diluted Earnings Per Share, Amount	[1]	47,246	66,804	96,208
Performance shares payout based upon performance		0	0	0
[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.

Accumulated Other Comprehensi67

Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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	(7,116)	$ (13,914)
Accumulated Defined Benefit Plans Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	(29,869)	(34,884)	$ (21,330)
Other Comprehensive Income (Loss) before Reclassifications	7,363	3,777	(12,628)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(1,422)	1,238	(926)
Accumulated Other Comprehensive Income (Loss), ending balance	(23,928)	(29,869)	(34,884)
Accumulated Net Unrealized Investment Gain (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	27,765	38,957	36,240
Other Comprehensive Income (Loss) before Reclassifications	6,904	(2,255)	8,694
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(6,206)	(8,937)	(5,977)
Accumulated Other Comprehensive Income (Loss), ending balance	28,463	27,765	38,957
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	(11,810)	(12,074)	(12,298)
Other Comprehensive Income (Loss) before Reclassifications	0	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	159	264	224
Accumulated Other Comprehensive Income (Loss), ending balance	(11,651)	(11,810)	(12,074)
Accumulated Other Comprehensive Income (Loss), Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	(13,914)	(8,001)	2,612
Other Comprehensive Income (Loss) before Reclassifications	14,267	1,522	(3,934)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(7,469)	(7,435)	(6,679)
Accumulated Other Comprehensive Income (Loss), ending balance	$ (7,116)	$ (13,914)	$ (8,001)

Accumulated Other Comprehensi68

Accumulated Other Comprehensive Income Amounts Reclassified (Details) - USD ($) $ in Thousands		3 Months Ended									12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	[1]	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income (Loss) before income tax											$ 150,686	$ 116,813	$ 132,516
Income tax expense											(53,918)	(34,895)	(41,088)
Net (Income) Loss		$ 5,656	$ 74,636		$ 22,284	$ (5,808)	$ 648	$ 56,740	$ 21,072	$ 3,458	96,768	81,918	91,428
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	[2]										7,407	6,574	7,659
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	[2]										(4,965)	(8,622)	(6,182)
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[2]										2,442	(2,048)	1,477
Reclassification from AOCI, Current Period, Tax											(1,020)	810	(551)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax											1,422	(1,238)	926
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax											6,206	8,937	5,977
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											(159)	(264)	(224)
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											(7,469)	(7,435)	(6,679)
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											7,640	11,114	7,350
Income (Loss) before income tax											7,640	11,114	7,350
Income tax expense											(1,434)	(2,177)	(1,373)
Net (Income) Loss											6,206	8,937	5,977
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											(498)	(467)	(438)
Income tax expense											339	203	214
Net (Income) Loss											(159)	(264)	(224)
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											$ (498)	$ (467)	$ (438)
[1]	For financial reporting purposes, the Company deferred any recognition of the Company's request in its 2015 Texas Retail Rate Case until it received the PUCT Final Order on August 25, 2016. Accordingly, it reported in the third quarter of 2016 the cumulative effect of the PUCT Final Order which related back to January 12, 2016. See Part II, Item 8, Financial Statements and Supplementary Data, Note C.
[2]	These items are included in the computation of net periodic benefit cost. See Part II, Item 8, Financial Statements and Supplementary Data, Note M for additional information.

Long-Term Debt and Financing 69

Long-Term Debt and Financing Obligations Outstanding Balance (Details) $ in Thousands		Jan. 10, 2017	Jan. 09, 2017USD ($)	Dec. 31, 2016USD ($)	Mar. 24, 2016USD ($)	Dec. 31, 2015USD ($)		Aug. 15, 2015USD ($)	Dec. 01, 2014USD ($)	Dec. 06, 2012USD ($)	Aug. 31, 2010USD ($)	Aug. 18, 2010USD ($)	Jun. 02, 2008	May 02, 2005	Jun. 29, 2008USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)		Dec. 31, 2014USD ($)	Aug. 28, 2012	Jun. 01, 2008USD ($)	May 01, 2005USD ($)
Debt Instrument [Line Items]
Long-term Debt				$ 1,360,230		$ 1,264,398	[1]									$ 1,360,230	$ 1,264,398	[1]
Long-term Debt, Current Maturities				(83,143)		0	[1]									(83,143)	0	[1]
Line of Credit, Current				(81,574)		(141,738)	[1]									(81,574)	(141,738)	[1]
Long-term debt, net of current portion				1,195,513		1,122,660	[1]									1,195,513	1,122,660	[1]
Proceeds from issuance of senior notes																157,052	0		$ 149,468
Interest accrued				13,287		12,649										13,287	12,649
Nuclear Fuel Financing
Debt Instrument [Line Items]
Long-term Line of Credit				37,600		33,700										37,600	33,700
Working Capital and General Purpose
Debt Instrument [Line Items]
Long-term Line of Credit				44,000		108,000										44,000	108,000
Short Term Borrowing
Debt Instrument [Line Items]
Repayments of Short-term Debt															$ 44,000
Revolving Credit Facility
Debt Instrument [Line Items]
Long-term Line of Credit				$ 81,574												$ 81,574
Line of Credit Weighted Average Interest Rate				2.00%												2.00%
Revolving Credit Facility | Nuclear Fuel Financing
Debt Instrument [Line Items]
Long-term Line of Credit				$ 37,600												$ 37,600
Revolving Credit Facility | Working Capital and General Purpose
Debt Instrument [Line Items]
Long-term Line of Credit				$ 44,000												44,000
Revolving Credit Facility Expiring January 2019
Debt Instrument [Line Items]
Line of Credit Facility, Expiration Date				Jan. 14, 2019
Line of Credit Facility, Current Borrowing Capacity				$ 300,000												300,000
Line of Credit Facility, Remaining Borrowing Capacity				100,000												100,000
Bonds and Notes
Debt Instrument [Line Items]
Long-term Debt				1,278,656		1,122,660	[1]									1,278,656	1,122,660	[1]
Pollution Control Bonds
Debt Instrument [Line Items]
Long-term Debt	[2]			$ 190,775		190,499	[1]									$ 190,775	190,499	[1]
Number of tax exempt bond series				4												4
Debt Instrument, Face Amount				$ 193,100												$ 193,100
Pollution Control Bonds | 7.25% 2009 Series A Refunding Bonds, due 2040
Debt Instrument [Line Items]
Long-term Debt	[2]			$ 62,619		$ 62,582	[1]									$ 62,619	$ 62,582	[1]
Debt Instrument, Interest Rate, Stated Percentage				7.25%		7.25%										7.25%	7.25%
Debt Instrument, Interest Rate, Effective Percentage				7.46%		7.46%										7.46%	7.46%
Debt Instrument, Maturity Date				Feb. 1, 2040		Feb. 1, 2040
Pollution Control Bonds | 4.50% 2012 Series A Refunding Bonds, due 2042
Debt Instrument [Line Items]
Long-term Debt	[2]			$ 58,471		$ 58,441	[1]									$ 58,471	$ 58,441	[1]
Debt Instrument, Interest Rate, Stated Percentage				4.50%		4.50%										4.50%	4.50%
Debt Instrument, Interest Rate, Effective Percentage				4.63%		4.63%										4.63%	4.63%
Debt Instrument, Maturity Date				Aug. 1, 2042		Aug. 1, 2042
Pollution Control Bonds | 7.25% 2009 Series B Refunding Bonds, due 2040
Debt Instrument [Line Items]
Long-term Debt	[2]			$ 36,492		$ 36,465	[1]									$ 36,492	$ 36,465	[1]
Debt Instrument, Interest Rate, Stated Percentage				7.25%		7.25%										7.25%	7.25%
Debt Instrument, Interest Rate, Effective Percentage				7.49%		7.49%										7.49%	7.49%
Debt Instrument, Maturity Date				Apr. 1, 2040		Apr. 1, 2040
Pollution Control Bonds | 1.875% 2012 Series A Refunding Bonds, due 2032
Debt Instrument [Line Items]
Long-term Debt	[2]			$ 33,193		$ 33,011	[1]									$ 33,193	$ 33,011	[1]
Debt Instrument, Interest Rate, Stated Percentage				1.875%		1.875%										1.875%	1.875%			1.875%
Debt Instrument, Interest Rate, Effective Percentage				2.35%		2.35%										2.35%	2.35%
Debt Instrument, Maturity Date				Jun. 1, 2032		Jun. 1, 2032
Debt Instrument Remarketed Date, Year				Sep. 30, 2017
Debt Instrument, Face Amount				$ 33,300												$ 33,300
Senior Notes
Debt Instrument [Line Items]
Long-term Debt	[3]			993,086		$ 837,475	[1]									993,086	$ 837,475	[1]
Senior Notes | 6.00% Senior Notes, Net of Discount, due 2035
Debt Instrument [Line Items]
Long-term Debt	[3]			$ 393,861		$ 393,693	[1]									$ 393,861	$ 393,693	[1]
Debt Instrument, Interest Rate, Stated Percentage				6.00%		6.00%										6.00%	6.00%					6.00%
Debt Instrument, Interest Rate, Effective Percentage				7.12%		7.12%										7.12%	7.12%
Debt Instrument, Maturity Date				May 15, 2035		May 15, 2035
Debt Instrument, Face Amount																						$ 400,000
Debt Instrument, Issuance Date														May 1, 2005
Debt Instrument, Unamortized Discount																						$ 2,300
Senior Notes | 7.50% Senior Notes, Net of Discount, due 2038
Debt Instrument [Line Items]
Long-term Debt	[3]			$ 147,331		$ 147,282	[1]									$ 147,331	$ 147,282	[1]
Debt Instrument, Interest Rate, Stated Percentage				7.50%		7.50%										7.50%	7.50%				7.50%
Debt Instrument, Interest Rate, Effective Percentage				7.67%		7.67%										7.67%	7.67%
Debt Instrument, Maturity Date				Mar. 15, 2038		Mar. 15, 2038
Debt Instrument, Face Amount																					$ 150,000
Debt Instrument, Issuance Date													Jun. 1, 2008
Debt Instrument, Unamortized Discount																					$ 1,300
Senior Notes | 3.30% Senior Notes, Net of Discount, due 2022
Debt Instrument [Line Items]
Long-term Debt	[3]			$ 148,939		$ 148,783	[1]									$ 148,939	$ 148,783	[1]
Debt Instrument, Interest Rate, Stated Percentage				3.30%		3.30%				3.30%						3.30%	3.30%
Debt Instrument, Interest Rate, Effective Percentage				3.43%		3.43%										3.43%	3.43%
Debt Instrument, Maturity Date				Dec. 15, 2022		Dec. 15, 2022
Debt Instrument, Face Amount										$ 150,000
Debt Instrument, Issuance Date										Dec. 1, 2012
Debt Instrument, Unamortized Discount										$ 300
Senior Notes | 5.00% Senior Notes, Net of Discount, due 2044
Debt Instrument [Line Items]
Long-term Debt	[3]			$ 302,955		$ 147,717	[1]									$ 302,955	$ 147,717	[1]
Debt Instrument, Interest Rate, Stated Percentage				5.00%	5.00%	5.00%										5.00%	5.00%
Debt Instrument, Interest Rate, Effective Percentage				4.93%		4.93%										4.93%	4.93%
Debt Instrument, Maturity Date				Dec. 1, 2044	Dec. 1, 2044	Dec. 1, 2044
Debt Instrument, Face Amount				$ 300,000	$ 150,000				$ 150,000							$ 300,000
Proceeds from issuance of senior notes					158,100
Interest accrued					2,400
Debt Instrument, Unamortized Premium					$ 7,100
Debt Instrument, Issuance Date					Mar. 24, 2016				Dec. 1, 2014
Debt Instrument, Unamortized Discount									$ 500
RGRT Senior Notes
Debt Instrument [Line Items]
Long-term Debt	[4]			94,795		$ 94,686	[1]									94,795	$ 94,686	[1]
Debt Instrument, Face Amount												$ 110,000
Redemption Price of Notes Equal to Principal Amount, Percentage												100.00%
Proceeds from Issuance of Long-term Debt											$ 109,400
RGRT Senior Notes | 3.67% Senior Notes, Series A, due 2015
Debt Instrument [Line Items]
Long-term Debt, Current Maturities								$ (15,000)
Debt Instrument, Interest Rate, Stated Percentage								3.67%
Debt Instrument, Maturity Date								Aug. 15, 2015
RGRT Senior Notes | 4.47% Senior Notes, Series B, due 2017
Debt Instrument [Line Items]
Long-term Debt	[4]			49,950		$ 49,883	[1]									49,950	$ 49,883	[1]
Long-term Debt, Current Maturities				$ (50,000)												$ (50,000)
Debt Instrument, Interest Rate, Stated Percentage				4.47%		4.47%										4.47%	4.47%
Debt Instrument, Interest Rate, Effective Percentage				4.62%		4.62%										4.62%	4.62%
Debt Instrument, Maturity Date				Aug. 15, 2017		Aug. 15, 2017
RGRT Senior Notes | 5.04% Senior Notes, Series C, due 2020
Debt Instrument [Line Items]
Long-term Debt	[4]			$ 44,845		$ 44,803	[1]									$ 44,845	$ 44,803	[1]
Debt Instrument, Interest Rate, Stated Percentage				5.04%		5.04%										5.04%	5.04%
Debt Instrument, Interest Rate, Effective Percentage				5.16%		5.16%										5.16%	5.16%
Debt Instrument, Maturity Date				Aug. 15, 2020		Aug. 15, 2020
Financing Obligations | Revolving Credit Facility
Debt Instrument [Line Items]
Long-term Line of Credit	[5]			$ 81,574		$ 141,738	[1]									$ 81,574	$ 141,738	[1]
Subsequent Event
Debt Instrument [Line Items]
Line of Credit Facility, Expiration Date		Jan. 14, 2021
Line of Credit renewal term, year		1 year
Subsequent Event | Revolving Credit Facility Expiring January 2020
Debt Instrument [Line Items]
Line of Credit Facility, Expiration Date			Jan. 14, 2020
Line of Credit renewal term, year			1 year
Line of Credit Facility, Current Borrowing Capacity			$ 350,000
Line of Credit Facility, Remaining Borrowing Capacity			50,000
Line of Credit Facility, Maximum Borrowing Capacity			400,000
Line of Credit Facility, Increase (Decrease), Net			$ 50,000
[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]	Pollution Control Bonds ("PCBs")The Company has four series of tax exempt unsecured PCBs in aggregate principal amount of $193.1 million. The 1.875% 2012 Series A (El Paso Electric Company Four Corners Project) Pollution Control Refunding Revenue Bonds with an aggregate principal amount of $33.3 million are subject to mandatory tender for purchase in September 2017 at which time the Company will either repay or remarket these bonds.
[3]	Senior NotesThe Senior Notes are unsecured obligations of the Company. They were issued pursuant to bond covenants that provide limitations on the Company’s ability to enter into certain transactions. The 6.00% Senior Notes have an aggregate principal amount of $400.0 million and were issued in May 2005. The proceeds, net of a $2.3 million discount, were used to fund the retirement of the Company's first mortgage bonds. The Company amortizes the loss associated with a cash flow hedge recorded in accumulated other comprehensive income to earnings as interest expense over the life of the 6.00% Senior Notes. See Part II, Item 8, Financial Statements and Supplementary Data, Note O. This amortization is included in the effective interest rate of the 6.00% Senior Notes. The 7.50% Senior Notes have an aggregate principal amount of $150.0 million and were issued in June 2008. The proceeds, net of a $1.3 million discount, were used to repay short-term borrowings of $44.0 million, fund capital expenditures and for other general corporate purposes.The 3.30% Senior Notes have an aggregate principal amount of $150.0 million were issued in December 2012. The proceeds, net of a $0.3 million discount, were used to fund construction expenditures and for working capital and general corporate purposes. In December 2014, the Company issued 5.00% Senior Notes with an aggregate principal amount of $150.0 million. The proceeds, net of a $0.5 million discount, were used to fund construction expenditures and for working capital and general corporate purposes. In March 2016, the Company issued additional 5.00% Senior Notes with an aggregate principal amount of $150.0 million. The proceeds from this issuance, after deducting the underwriters' commission, were $158.1 million. These proceeds included accrued interest of $2.4 million and a $7.1 million premium before expenses. The net proceeds, from the sale of these senior notes were used to repay outstanding short-term borrowings under the RCF. After the March 2016 issuance, the Company's 5.00% Senior Notes due 2044 had a total principal amount outstanding of $300.0 million.
[4]	RGRT Senior NotesIn 2010, the Company and RGRT, a Texas grantor trust through which the Company finances its portion of fuel for Palo Verde, entered into a note purchase agreement with various institutional purchasers. Under the terms of the agreement, RGRT sold to the purchasers $110 million aggregate principal amount of Senior Notes (the "Notes"). In August 2015, $15.0 million of these Notes matured and were paid with borrowings from the RCF. In August 2017, $50.0 million of these Senior Notes will mature. The Company will either repay or refinance this $50.0 million of Notes upon maturity. The Company guarantees the payment of principal and interest on the Notes. In the Company’s financial statements, the assets and liabilities of RGRT are reported as assets and liabilities of the Company.RGRT pays interest on the Notes on February 15, and August 15 of each year until maturity. RGRT may redeem the Notes, in whole or in part, at any time at a redemption price equal to 100% of the principal amount to be redeemed together with the interest on such principal amount accrued to the date of redemption, plus a make-whole amount based on the prevailing market interest rates. The agreement requires compliance with certain covenants, including a total debt to capitalization ratio. The Company was in compliance with these requirements throughout 2016.The sale of the Notes was made by RGRT in reliance on a private placement exemption from registration under the Securities Act of 1933, as amended. The proceeds of $109.4 million, net of issuance costs, from the sale of the Notes was used by RGRT to repay amounts borrowed under the RCF and will enable future nuclear fuel financing requirements of RGRT to be met with a combination of the Notes and amounts borrowed from the RCF.
[5]	Revolving Credit FacilityOn January 14, 2014, the Company and RGRT entered into a second amended and restated credit agreement related to the RCF with JP Morgan Chase Bank, N.A., as administrative agent and issuing bank, and Union Bank, N.A., as syndication agent, and various lending banks party thereto. As of December 31, 2016, the Company had available $300 million and the ability to increase the RCF by up to $100 million with a term ending January 2019. On January 9, 2017, the Company exercised its option to extend the maturity of the RCF by one year to January 14, 2020 and to increase the size of the facility by $50 million to $350 million. The Company still has the option to extend the facility by one additional year to January 2021 and to increase the RCF by up to $50 million (up to a total of $400 million) upon the satisfaction of certain conditions, more fully set forth in the agreement, including obtaining commitments from lenders or third party financial institutions.The RCF provides that amounts borrowed by the Company may be used for, among other things, working capital and general corporate purposes. Any amounts borrowed by RGRT may be used, among other things, to finance the acquisition and processing of nuclear fuel. Amounts borrowed by RGRT are guaranteed by the Company and the balance borrowed under the RCF is recorded as short-term borrowings on the balance sheet. The RCF is unsecured. The RCF requires compliance with certain covenants, including a total debt to capitalization ratio. The Company was in compliance with these requirements throughout 2016. In August 2015, $15.0 million aggregate principal amount of Series A 3.67% Senior Notes of RGRT matured and were paid utilizing borrowings under the RCF. As of December 31, 2016, the total amount borrowed by RGRT was $37.6 million for nuclear fuel under the RCF. As of December 31, 2016, $44.0 million of borrowings were outstanding under this facility for working capital and general corporate purposes. The weighted average interest rate on the RCF was 2.0% as of December 31, 2016.

Long-Term Debt and Financing 70

Long-Term Debt and Financing Obligations Long-term Debt Maturities (Details) $ in Thousands	Dec. 31, 2016USD ($)
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Year One	$ 83,300
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-term Debt, Maturities, Repayments of Principal in Year Three	0
Long-term Debt, Maturities, Repayments of Principal in Year Four	45,000
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Nuclear Fuel Financing | Revolving Credit Facility
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Year One	$ 37,600

Long-Term Debt and Financing 71

Long-Term Debt and Financing Obligations Reclassification (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Accounting Standards Update 2015-03 [Member]
Debt Instrument [Line Items]
Amounts previously reported, reclassified	$ 11.6

Income Taxes (Deferred Tax Asse

Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Benefit of tax loss carryforwards	$ 60,749	$ 35,153
Alternative minimum tax credit carryforward	16,620	16,620
Pensions and benefits	57,756	61,673
Asset retirement obligation	26,929	28,042
Deferred fuel	0	1,488
Other	(200)	15,421
Total gross deferred tax assets	161,854	158,397
Deferred tax liabilities:
Plant, principally due to depreciation and basis differences	(668,303)	(608,738)
Decommissioning	(43,463)	(41,100)
Deferred fuel	3,962	0
Other	(1,192)	(3,796)
Total gross deferred tax liabilities	(716,920)	(653,634)
Net accumulated deferred income taxes	$ (555,066)	$ (495,237)

Income Taxes (Recognized Income

Income Taxes (Recognized Income Tax Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Federal:
Current	$ 2,642	$ 2,319	$ (1,250)
Deferred	47,909	32,819	38,810
Total federal income tax	50,551	35,138	37,560
State:
Current	766	1,730	3,209
Deferred	3,285	(1,650)	641
Total state income tax	4,051	80	3,850
Generation (amortization) of accumulated investment tax credits	(684)	(323)	(322)
Total income tax expense	$ 53,918	$ 34,895	$ 41,088

Income Taxes (Income Tax Provis

Income Taxes (Income Tax Provisions) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Examination [Line Items]
Federal income tax expense computed on income at statutory rate	$ 52,740	$ 40,885	$ 46,381
Difference due to:
State taxes, net of federal benefit	2,633	52	1,902
AEFUDC	(475)	(2,345)	(3,757)
Permanent tax differences	(2,369)	(2,898)	(2,921)
Other	1,389	(799)	(517)
Total income tax expense	$ 53,918	$ 34,895	$ 41,088
Effective income tax rate	35.80%	29.90%	31.00%

Income Taxes (Unrecognized Tax

Income Taxes (Unrecognized Tax Benefits)[Roll Forward] (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 6,000	$ 5,200	$ 7,200
Additions for tax positions related to the current year	400	500	300
Reductions for tax positions related to the current year	0	0	0
Additions for tax positions of prior years	100	300	2,200
Reductions for tax positions of prior years	(1,200)	0	(4,500)
Balance at end of period	$ 5,300	$ 6,000	$ 5,200

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax [Line Items]
Period of Average Annual Book Income Before Taxes		3 years
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax		$ 16,620	$ 16,620
Federal statutory tax rate		35.00%	35.00%	35.00%
Deferred Income Tax Expense (Benefit)		$ 50,510	$ 30,846	$ 39,129
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions		0	0	0
Unrecognized tax benefits, Increase (Decrease) resulting from tax positions taken in prior and current period tax returns.		(400)	(800)	(2,100)
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities		500
Unrecognized tax benefits that would impact effective tax rate		2,600
Unrecognized tax benefits, interest on income taxes expense (benefit)		100	200	100
Unrecognized tax benefits, income tax penalties and interest accrued		800	700
Unrecognized Tax Benefits		5,300	$ 6,000	5,200	$ 7,200
Internal Revenue Service (IRS)
Income Tax [Line Items]
Tax Credit Carryforward, Amount		$ 59,300
Live Of Tax Loss Carrforwards		20 years
State and Local Jurisdiction
Income Tax [Line Items]
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions		$ 700
Tax Credit Carryforward, Amount		$ 2,200
Live Of Tax Loss Carrforwards		5 years
Tax credit taken | ARIZONA
Income Tax [Line Items]
Increase (Decrease) in Unrecognized Tax Position of Prior Years Recorded, net		$ (300)		(1,300)
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities				$ 400
Earliest Tax Year | TEXAS
Income Tax [Line Items]
Income Tax Examination, Year under Examination		2,007
Earliest Tax Year | ARIZONA
Income Tax [Line Items]
Tax Year Closed	2,009
Latest Tax Year | Internal Revenue Service (IRS)
Income Tax [Line Items]
Tax Year Closed		2,011
Latest Tax Year | NEW MEXICO
Income Tax [Line Items]
Tax Year Closed		2,011
Latest Tax Year | TEXAS
Income Tax [Line Items]
Income Tax Examination, Year under Examination		2,011
Latest Tax Year | ARIZONA
Income Tax [Line Items]
Tax Year Closed	2,012
Change in Accounting Method Accounted for as Change in Estimate [Member]
Income Tax [Line Items]
Deferred Income Tax Expense (Benefit)		$ 5,100
Stock Compensation Plan
Income Tax [Line Items]
Unrecognized Tax Benefits		200
Accounting Standards Update 2015-17 [Member]
Income Tax [Line Items]
Prior Period Reclassification Adjustment		$ 21,600

Commitments, Contingencies an77

Commitments, Contingencies and Uncertainties (Power Purchase and Sale Agreement) (Details)	12 Months Ended
	Dec. 31, 2016MW
Freeport Agreement 3 - 25 MW
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	25
Long-term Purchase Commitment, Time Period	10 years 1 month
Long-Term Sale Commitment, Maximum Quantity	25
Long-Term Sale Commitment, Time Period	10 years 1 month
Freeport Agreement 2 - 100 MW
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	100
Long-term Purchase Commitment, Time Period	15 years 7 months
Long-Term Sale Commitment, Maximum Quantity	100
Long-Term Sale Commitment, Time Period	15 years 7 months
Hatch Solar Energy Center I
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	5
Long-term Purchase Commitment, Time Period	25 years
Plant Commercial Operation Date	Jul. 1, 2011
NRG
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	20
Long-term Purchase Commitment, Time Period	20 years 1 month
Plant Commercial Operation Date	Aug. 1, 2011
Sun Edison 1
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	10
Long-term Purchase Commitment, Time Period	25 years 1 month
Plant Commercial Operation Date	Jun. 25, 2012
Sun Edison 2
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	12
Long-term Purchase Commitment, Time Period	25 years 1 month
Plant Commercial Operation Date	May 2, 2012
Macho Springs Solar
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	50
Long-term Purchase Commitment, Time Period	20 years
Plant Commercial Operation Date	May 23, 2014
Plant Capacity	50
Newman Solar
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	10
Long-term Purchase Commitment, Time Period	30 years
Plant Commercial Operation Date	Dec. 30, 2014
Freeport Agreement 1 - 125 MW
Long-term Purchase Commitment [Line Items]
Long-Term Purchase commitment, Maximum Quantity	125
Long-term Purchase Commitment, Time Period	2 years
Long-Term Sale Commitment, Maximum Quantity	125
Long-Term Sale Commitment, Time Period	2 years
Long-term Contract for Purchase of Electric Power, Date of Contract Expiration	Dec. 31, 2018
Long-Term Contract For Sale Of Electric Power Date Of Contract Expiration	Dec. 31, 2018
Sun Edison 1 and Sun Edison 2
Long-term Purchase Commitment [Line Items]
Solar Photovoltaic Projects, Number of Units	2
FERC | Freeport Agreement 1 - 125 MW
Long-term Purchase Commitment [Line Items]
Long-term Contract for Purchase of Electric Power, Date of Contract Expiration	Dec. 31, 2021
Long-Term Contract For Sale Of Electric Power Date Of Contract Expiration	Dec. 31, 2021

Commitments, Contingencies an78

Commitments, Contingencies and Uncertainties (Narrative) (Details) - USD ($) $ in Thousands	Mar. 16, 2016	Aug. 17, 2015	Dec. 31, 2016
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies			$ 200
Four Corners Coal Plant Participants
Loss Contingencies [Line Items]
Civil Penalty Amount		$ 1,500
Public Utilities, Assessed Coal Severance Surtax Penalty and Interest			30,000
Litigation Settlement, Amount	$ 1,000
Environmental Mitigation Project Cost		$ 6,700
Four Corners Generating Station
Loss Contingencies [Line Items]
Public Utilities, Assessed Coal Severance Surtax Penalty and Interest			$ 1,500
Litigation Settlement, Amount	$ 47

Commitments, Contingencies an79

Commitments, Contingencies and Uncertainties (Future Minimum Payments For Operating Leases) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense	$ 1,700	$ 1,900	$ 1,800
2,017	808
2,018	662
2,019	666
2,020	664
2,021	$ 562
Newman Land Lease
Operating Leased Assets [Line Items]
Lease Expiration Date	Jun. 30, 2033
Lessee Leasing Arrangements, Operating Leases, Renewal Term	25 years
Other Property
Operating Leased Assets [Line Items]
Lessee Leasing Arrangements, Operating Leases, Term of Contract	P4Y

Commitments, Contingencies an80

Commitments, Contingencies and Uncertainties (Union Matters) (Details)	12 Months Ended
	Dec. 31, 2016	Sep. 03, 2018	Sep. 03, 2017	Sep. 03, 2016
Commitments and Contingencies Disclosure [Abstract]
Entity Number of Employees	1,100
Number of Employees Cover by Collective Bargaining Agreements, Percentage	38.00%
Collective Bargaining Agreement Effective Date	Sep. 3, 2016
Term of Collective Bargaining Agreement, Year	P3Y
Collective Bargaining Agreement Expiration Date	Sep. 3, 2019
Subsequent Event [Line Items]
Pay increase, percentage				3.00%
Scenario, Forecast
Subsequent Event [Line Items]
Pay increase, percentage		3.00%	3.00%

Employee Benefits (Obligations

Employee Benefits (Obligations and Funded Status of the Plan) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Retirement Income Plan
Change in projected benefit obligation:
Benefit obligation at end of prior year	$ 325,706	$ 341,133
Service cost	7,705	8,530	$ 8,284
Interest cost	12,161	13,477	14,001
Actuarial (gain) loss	7,988	(19,290)
Benefits paid	(15,792)	(18,144)
Benefit obligation at end of year	337,768	325,706	341,133
Change in plan assets:
Fair value of plan assets at end of prior year	260,035	272,939
Actual return (loss) on plan assets	18,223	(3,760)
Employer contribution	7,300	9,000
Benefits paid	(15,792)	(18,144)
Fair value of plan assets at end of year	269,766	260,035	272,939
Funded status at end of year	(68,002)	(65,671)
Other Pension Plans
Change in projected benefit obligation:
Benefit obligation at end of prior year	26,958	28,397
Service cost	296	262	303
Interest cost	878	1,018	1,041
Actuarial (gain) loss	1,267	(810)
Benefits paid	(1,937)	(1,909)
Benefit obligation at end of year	27,462	26,958	28,397
Change in plan assets:
Fair value of plan assets at end of prior year	0	0
Actual return (loss) on plan assets	0	0
Employer contribution	1,937	1,909
Benefits paid	(1,937)	(1,909)
Fair value of plan assets at end of year	0	0	$ 0
Funded status at end of year	$ (27,462)	$ (26,958)

Employee Benefits (Defined Bene

Employee Benefits (Defined Benefit Plan, Amounts Recognized in Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current liabilities	$ 0	$ 0
Noncurrent liabilities	(68,002)	(65,671)
Total	(68,002)	(65,671)
Other Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current liabilities	(2,696)	(2,102)
Noncurrent liabilities	(24,766)	(24,856)
Total	(27,462)	(26,958)
Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current liabilities	0	0
Noncurrent liabilities	(34,400)	(54,553)
Total	$ (34,400)	$ (54,553)

Employee Benefits (Accumulated

Employee Benefits (Accumulated Benefit Obligations in Excess of Fair Value of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Projected benefit obligation	$ (337,768)	$ (325,706)
Accumulated benefit obligation	(314,071)	(302,446)
Fair value of plan assets	269,766	260,035
Other Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Projected benefit obligation	(27,462)	(26,958)
Accumulated benefit obligation	(25,550)	(25,785)
Fair value of plan assets	$ 0	$ 0

Employee Benefits (Amounts Reco

Employee Benefits (Amounts Recognized in Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	$ 121,052	$ 118,963
Prior service benefit	(23,877)	(27,344)
Total	97,175	91,619
Other Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	10,073	9,592
Prior service benefit	(185)	(224)
Total	$ 9,888	$ 9,368

Employee Benefits (Weighted-Ave

Employee Benefits (Weighted-Average Actuarial Assumptions for Benefit Obligations - Retirement Plans) (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Effect of One Percentage Point Increase on Discount Rate	1.00%
Defined Benefit Plan, Decrease in Projected Benefit Obiligation, Percentage	11.50%
Defined Benefit Plan, Effect of One Percentage Point Decrease on Discount Rate	1.00%
Defined Benefit Plan, Increase in Projected Benefit Obiligation, Percentage	14.10%
Retirement Income Plan | Benefit Obligations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.29%	4.57%
Rate of compensation increase	4.50%	4.50%
Supplemental Employee Retirement Plan | Benefit Obligations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.76%	3.99%
Excess Benefit Plan | Benefit Obligations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.34%	4.59%
Rate of compensation increase	4.50%	4.50%

Employee Benefits (Net Periodic

Employee Benefits (Net Periodic Benefit Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 7,705	$ 8,530	$ 8,284
Interest cost	12,161	13,477	14,001
Expected return on plan assets	(18,879)	(19,795)	(18,699)
Decrease In Service and Interest Component of Net Periodic Benefit Cost	2,900
Amortization of:
Net loss	6,554	9,710	8,178
Prior service cost (benefit)	(3,467)	(3,467)	(2,889)
Net periodic benefit cost	4,074	8,455	8,875
Other Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	296	262	303
Interest cost	878	1,018	1,041
Expected return on plan assets	0	0	0
Amortization of:
Net loss	785	937	675
Prior service cost (benefit)	(39)	(39)	(17)
Net periodic benefit cost	$ 1,920	$ 2,178	$ 2,002

Employee Benefits (Other Compre

Employee Benefits (Other Comprehensive Income - Retirement Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net (gain) loss	$ 20,053	$ (5,429)	$ 54,328
Prior service benefit	(32,697)	(824)	(34,200)
Amortization of:
Net loss	(4,965)	(8,622)	(6,182)
Prior service (cost) benefit	7,407	6,574	7,659
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net (gain) loss	8,644	4,266	47,324
Prior service benefit	0	0	(33,700)
Amortization of:
Net loss	(6,554)	(9,710)	(8,178)
Prior service (cost) benefit	3,467	3,467	2,889
Total recognized in other comprehensive income	5,557	(1,977)	8,335
Other Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net (gain) loss	1,266	(811)	3,508
Prior service benefit	0	0	(500)
Amortization of:
Net loss	(785)	(937)	(675)
Prior service (cost) benefit	39	39	17
Total recognized in other comprehensive income	$ 520	$ (1,709)	$ 2,350

Employee Benefits (Recognized i

Employee Benefits (Recognized in Other Comprehensive Income and Net Periodic Benefit Costs - Retirement Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total recognized in net periodic benefit cost and other comprehensive income	$ 9,631	$ 6,478	$ 17,210
Other Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total recognized in net periodic benefit cost and other comprehensive income	$ 2,440	$ 469	$ 4,352

Employee Benefits (Accumulate89

Employee Benefits (Accumulated Other Comprehensive Income Recognized in Net Periodic Benefit Cost in Next Fiscal Year) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss/gain	$ 7,530
Prior service benefit	(3,470)
Other Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss/gain	825
Prior service benefit	(40)
Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss/gain	(1,600)
Prior service benefit	$ (6,200)

Employee Benefits (Weighted Ave

Employee Benefits (Weighted Average Assumptions Used to Calculate Net Period Benefit Costs- Retirement Plans) (Details)	Jan. 01, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	[1]	Feb. 28, 2014	Dec. 31, 2013
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term return on plan assets		7.00%
Net Periodic Benefit Costs | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term return on plan assets		7.00%	7.50%	7.50%
Rate of compensation increase		4.50%	4.50%	4.75%
Net Periodic Benefit Costs | Excess Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase		4.50%	4.50%	4.75%
Subsequent Event | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term return on plan assets	7.00%
Remeasurement | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate - Benefit Obligations						4.60%	4.90%
Remeasurement | Excess Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate - Benefit Obligations						4.50%	4.90%
Benefit Obligation | Net Periodic Benefit Costs | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate		4.57%	4.00%	4.90%
Benefit Obligation | Net Periodic Benefit Costs | Supplemental Employee Retirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate		3.99%	3.40%	3.90%
Benefit Obligation | Net Periodic Benefit Costs | Excess Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate		4.63%	4.10%	4.90%
Service cost | Net Periodic Benefit Costs | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate		4.83%	4.00%	4.90%
Service cost | Net Periodic Benefit Costs | Excess Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate		4.87%	4.10%	4.90%
Interest cost | Net Periodic Benefit Costs | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate		3.86%	4.00%	4.90%
Interest cost | Net Periodic Benefit Costs | Supplemental Employee Retirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate		3.04%	3.40%	3.90%
Interest cost | Net Periodic Benefit Costs | Excess Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate		3.90%	4.10%	4.90%
[1]	The Retirement Plan and the Excess Benefit Plan were remeasured on February 28, 2014 due to the above mentioned plan amendment. The discount rate used to remeasure the benefit obligation was 4.6% for the Retirement Plan and 4.5% for the Excess Benefit Plan, compared to 4.9% for both plans as of January 1, 2014. All other assumptions remained consistent with assumptions used at January 1, 2014.

Employee Benefits (Target Asset

Employee Benefits (Target Asset Allocation of Pension Fund) (Details) - Retirement Income Plan	12 Months Ended
	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assets, Target Allocations Total	100.00%
Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assets, Target Allocations	50.00%
Fixed Income
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assets, Target Allocations	40.00%
Alternative Investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assets, Target Allocations	10.00%

Employee Benefits (Fair Value M

Employee Benefits (Fair Value Measurement Inputs) (Details) - USD ($)		Jun. 30, 2016	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value, Assets, Level 1 to Level 2 Transfers, Description			no		no
Fair Value, Assets, Level 2 to Level 1 Transfers, Description			no		no
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, Sales, Issuances, Settlements			$ 0		$ 0
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Restriction Period To Sell Partnership Interest Maximum			7 years
Fair value of plan assets at end of year			$ 269,766,000		$ 260,035,000		$ 272,939,000
Fair Value, Assets, Level 1 to Level 2 Transfers, Description			no		no
Fair Value, Assets, Level 2 to Level 1 Transfers, Description			no		no
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, Sales, Issuances, Settlements			$ 0		$ 0
Limited Partnership expiration date		Jun. 30, 2016
Cash and Cash Equivalents | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			932,000		1,266,000
Common Collective Trusts | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		261,843,000		250,181,000
Limited Partnership Interest in Real Estate | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			6,991,000	[2],[3]	8,588,000	[2],[3]	$ 8,748,000
Fair Value, Inputs, Level 1 | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			262,775,000		251,447,000
Fair Value, Inputs, Level 1 | Cash and Cash Equivalents | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			932,000		1,266,000
Fair Value, Inputs, Level 1 | Common Collective Trusts | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		261,843,000		250,181,000
Fair Value, Inputs, Level 2 | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			0		0
Fair Value, Inputs, Level 2 | Cash and Cash Equivalents | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			0		0
Fair Value, Inputs, Level 2 | Common Collective Trusts | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Fair Value, Inputs, Level 3 | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			0		0
Fair Value, Inputs, Level 3 | Cash and Cash Equivalents | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			0		0
Fair Value, Inputs, Level 3 | Common Collective Trusts | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Common Collective Trusts | Equity Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		144,081,000		144,279,000
Common Collective Trusts | Fixed Income Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		109,356,000		103,877,000
Common Collective Trusts | Real Estate Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		8,406,000		2,025,000
Common Collective Trusts | Fair Value, Inputs, Level 1 | Equity Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		144,081,000		144,279,000
Common Collective Trusts | Fair Value, Inputs, Level 1 | Fixed Income Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		109,356,000		103,877,000
Common Collective Trusts | Fair Value, Inputs, Level 1 | Real Estate Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		8,406,000		2,025,000
Common Collective Trusts | Fair Value, Inputs, Level 2 | Equity Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Common Collective Trusts | Fair Value, Inputs, Level 2 | Fixed Income Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Common Collective Trusts | Fair Value, Inputs, Level 2 | Real Estate Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Common Collective Trusts | Fair Value, Inputs, Level 3 | Equity Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Common Collective Trusts | Fair Value, Inputs, Level 3 | Fixed Income Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Common Collective Trusts | Fair Value, Inputs, Level 3 | Real Estate Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		$ 0		$ 0
[1]	The Common Collective Trusts are invested in equity and fixed income securities, or a combination thereof. The investment objective of each fund is to produce returns in excess of, or commensurate with, its predefined index.
[2]	In the first quarter of 2016, the Company implemented ASU 2015-07, Fair Value Measurement (Topic 820) which eliminates the requirement to categorize investments in the fair value hierarchy if the fair value is measured at NAV per share (or its equivalent) using the practical expedient in the FASB’s fair value measurement guidance. The fair value amounts presented in the table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the statement of financial position. ASU 2015-07 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years.
[3]	This investment is a commercial real estate partnership that purchases land, develops limited infrastructure, and sells it for commercial development. The Company was restricted from selling its partnership interest during the life of the partnership, which spanned 7 years. Return on investment is realized as land is sold. The fair value of the limited partnership interest in real estate is based on the NAV of the partnership which reflects the appraised value of the land. The partnership term expired on June 30, 2016. Upon expiration, dissolution of the partnership commenced and, as a result, the general partner of the partnership is attempting to sell the remaining inventory as soon as possible at the highest pricing possible.

Employee Benefits (Fair Value C

Employee Benefits (Fair Value Change in Investment in Real Estate) (Details) - Retirement Income Plan - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of prior year		$ 260,035		$ 272,939
Fair value of plan assets at end of year		269,766		260,035
Limited Partnership Interest in Real Estate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of prior year		8,588	[1],[2]	8,748
Unrealized gain (loss) in fair value		(822)		(160)
Sale of Land		(775)
Fair value of plan assets at end of year	[1],[2]	$ 6,991		$ 8,588
[1]	In the first quarter of 2016, the Company implemented ASU 2015-07, Fair Value Measurement (Topic 820) which eliminates the requirement to categorize investments in the fair value hierarchy if the fair value is measured at NAV per share (or its equivalent) using the practical expedient in the FASB’s fair value measurement guidance. The fair value amounts presented in the table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the statement of financial position. ASU 2015-07 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years.
[2]	This investment is a commercial real estate partnership that purchases land, develops limited infrastructure, and sells it for commercial development. The Company was restricted from selling its partnership interest during the life of the partnership, which spanned 7 years. Return on investment is realized as land is sold. The fair value of the limited partnership interest in real estate is based on the NAV of the partnership which reflects the appraised value of the land. The partnership term expired on June 30, 2016. Upon expiration, dissolution of the partnership commenced and, as a result, the general partner of the partnership is attempting to sell the remaining inventory as soon as possible at the highest pricing possible.

Employee Benefits (Expected Fut

Employee Benefits (Expected Future Benefit Payments) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	$ 10,000
2,017	16,113
2,018	19,080
2,019	18,771
2,020	18,923
2,021	19,755
2022-2026	107,916
Other Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,017	2,698
2,018	2,060
2,019	2,025
2,020	1,957
2,021	1,907
2022-2026	$ 8,949

Employee Benefits 401(k) Define

Employee Benefits 401(k) Defined Contribution Plans (Details) - USD ($) $ in Millions	Apr. 02, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Contribution Plan Disclosure [Line Items]
Defined benefit plans revisions effective date	Apr. 1, 2014
Defined Contribution Plan, Employer Discretionary Contribution Amount			$ 4.1	$ 3.9	$ 3
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	100.00%	50.00%
Maximum
Defined Contribution Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent	6.00%	6.00%

Employee Benefits (Changes in F

Employee Benefits (Changes in Funded Status of Plan - Other Postretirment Benefit Plans) (Details) - Other Postretirement Benefit Plan $ in Thousands		12 Months Ended
		Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Jan. 01, 2017
Change in projected benefit obligation:
Benefit obligation at end of prior year		$ 92,643	$ 100,700
Service cost		2,769	3,454	$ 2,845
Interest cost		3,167	4,035	4,463
Actuarial loss (gain)		10,751	(11,423)
Amendment	[1],[2]	(32,697)	(824)
Benefits paid		(4,428)	(4,544)
Retiree contributions		1,310	1,245
Benefit obligation at end of year		73,515	92,643	100,700
Change in plan assets:
Fair value of plan assets at end of prior year		38,090	41,358
Actual return (loss) on plan assets		2,443	(469)
Employer contribution		1,700	500
Benefits paid		(4,428)	(4,544)
Retiree contributions		1,310	1,245
Fair value of plan assets at end of year		39,115	38,090	$ 41,358
Funded status at end of year		$ (34,400)	$ (54,553)
$1,000 or $2,250 deductible plan options | Scenario, Forecast | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Age Eligible for Benefit					65
Medicare advantage plan | Scenario, Forecast | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Age Eligible for Benefit					65
[1]	Amendment relates to modification of the Company's Other Post-retirement Benefit Plan which increased mail order co-payments for post age 65. The amendment was approved in 2015 and became effective January 1, 2016.
[2]	During October 2016, the Company approved and communicated a plan amendment that resulted in a remeasurement of the Company's Other Post-retirement Benefit Plan. Effective January 1, 2017, retirees and dependents that are less than 65 years of age are offered a choice between a $1,000 and $2,250 deductible plan. Additionally, retirees and dependents that are 65 years of age or greater were covered by a fully insured Medicare advantage plan.

Employee Benefits (Components o

Employee Benefits (Components of Accumulated Other Comprehensive Income) (Details) - Other Postretirement Benefit Plan - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net gain	$ (26,285)	$ (38,802)
Prior service benefit	(41,009)	(12,213)
Total	$ (67,294)	$ (51,015)

Employee Benefits (Weighted A98

Employee Benefits (Weighted Average Assumptions- Accrued Postretirement Benefits - Other Postretirment Benefit Plans) (Details) - Other Postretirement Benefit Plan		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation, Percentage		13.10%
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation, Percentage		16.70%
Accrued Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate		4.36%	4.59%
Ultimate		4.50%	4.50%
Year ultimate reached	[1]	2,026	2,026
Defined Benefit Plan, Effect of One Percentage Point Increase on Discount Rate		1.00%
Defined Benefit Plan, Effect of One Percentage Point Decrease on Discount Rate		1.00%
Pre-65 medical | Accrued Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Initial		6.50%	7.00%
Post-65 medical | Accrued Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Initial		4.50%	7.00%
Pre-65 drug | Accrued Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Initial		7.50%	7.00%
Post-65 drug | Accrued Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Initial		10.50%	7.00%
[1]	Pre-65 medical reaches the ultimate trend rate in 2025. Additionally, the Post-65 medical trend is assumed to be 4.50% for all years into the future.

Employee Benefits (Net Period99

Employee Benefits (Net Periodic Benefit Cost) (Details) - Other Postretirement Benefit Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Decrease In Service and Interest Component of Net Periodic Benefit Cost	$ 800
Service cost	2,769	$ 3,454	$ 2,845
Interest cost	3,167	4,035	4,463
Expected return on plan assets	(1,835)	(2,070)	(2,116)
Amortization of:
Prior service benefit	(3,901)	(3,068)	(4,753)
Net gain	(2,374)	(2,025)	(2,671)
Net periodic benefit cost	$ (2,174)	$ 326	$ (2,232)

Employee Benefits (Other Com100

Employee Benefits (Other Comprehensive Income, Other Postretirement Benefit Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net (gain) loss	$ 20,053	$ (5,429)	$ 54,328
Prior service benefit	(32,697)	(824)	(34,200)
Amortization of:
Prior service benefit	7,407	6,574	7,659
Net gain	(4,965)	(8,622)	(6,182)
Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net (gain) loss	10,143	(8,884)	3,496
Prior service benefit	(32,697)	(824)	0
Amortization of:
Prior service benefit	3,901	3,068	4,753
Net gain	2,374	2,025	2,671
Total recognized in other comprehensive income	$ (16,279)	$ (4,615)	$ 10,920

Employee Benefits (Recognized N

Employee Benefits (Recognized Net Periodic Benefit Costs and Other Comprehensive Income -Other Postretirement Benefit Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total recognized in net periodic benefit cost and other comprehensive income	$ (18,453)	$ (4,289)	$ 8,688

Employee Benefits (Weighted 102

Employee Benefits (Weighted Average Assumptions - Net Periodic Benefit Cost) (Details) - Other Postretirement Benefit Plan - USD ($) $ in Millions	Jan. 01, 2017	Dec. 31, 2016		Sep. 30, 2016	[1]	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, One Percentage Point Change, Increase or Decrease						1.00%
Defined Benefit Plan, Effect of One Percentage Point Increase on Benefit Obligations		$ 11.2				$ 11.2
Defined Benefit Plan, Effect of One Percentage Point Decrease on Benefit Obligations		$ 9				9
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components						1.3
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components						$ 1
Net Periodic Benefit Costs
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term return on plan assets						4.875%	[1]	5.20%	5.20%
Initial						7.00%	[1]	7.25%	7.50%
Ultimate						4.50%	[1]	4.50%	4.50%
Year ultimate reached		2,026	[1]			2,026	[1]	2,026	2,026
Subsequent Event
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term return on plan assets	4.875%
Benefit Obligation | Net Periodic Benefit Costs
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate		3.75%	[1]	4.59%				4.10%	4.90%
Service cost | Net Periodic Benefit Costs
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate		4.03%	[1]	4.91%				4.10%	4.90%
Interest cost | Net Periodic Benefit Costs
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate		3.15%	[1]	3.86%				4.10%	4.90%
[1]	The actuarial assumptions are evaluated by the Company at each measurement date. The Other Post-retirement Benefits Plan was remeasured at October 1, 2016 due to a plan amendment.

Employee Benefits (Target Alloc

Employee Benefits (Target Allocations - Other Postretirment Benefit Plans) (Details) - Other Postretirement Benefit Plan	12 Months Ended
	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assets, Target Allocations Total	100.00%
Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assets, Target Allocations	65.00%
Fixed Income
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assets, Target Allocations	30.00%
Alternative Investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assets, Target Allocations	5.00%

Employee Benefits (Fair Valu104

Employee Benefits (Fair Value Measurements- Other Postretirement Benefits) (Details) - USD ($)		Jun. 30, 2016	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value, Assets, Level 1 to Level 2 Transfers, Description			no		no
Fair Value, Assets, Level 2 to Level 1 Transfers, Description			no		no
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, Sales, Issuances, Settlements			$ 0		$ 0
Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Restriction Period To Sell Partnership Interest Maximum			7 years
Fair Value, Assets, Level 1 to Level 2 Transfers, Description			no		no
Fair Value, Assets, Level 2 to Level 1 Transfers, Description			no		no
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, Sales, Issuances, Settlements			$ 0		$ 0
Fair value of plan assets at end of year			39,115,000		38,090,000		$ 41,358,000
Limited Partnership expiration date		Jun. 30, 2016
Institutional Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		37,804,000		36,480,000
Limited Partnership Interest in Real Estate | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			1,311,000	[2],[3]	1,610,000	[2],[3]	$ 1,640,000
Fair Value, Inputs, Level 1 | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			37,804,000		36,480,000
Fair Value, Inputs, Level 1 | Institutional Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		37,804,000		36,480,000
Fair Value, Inputs, Level 2 | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			0		0
Fair Value, Inputs, Level 2 | Institutional Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Fair Value, Inputs, Level 3 | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			0		0
Fair Value, Inputs, Level 3 | Institutional Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Institutional Funds | Equity Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		26,133,000		24,881,000
Institutional Funds | Fixed Income Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		11,671,000		11,599,000
Institutional Funds | Fair Value, Inputs, Level 1 | Equity Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		26,133,000		24,881,000
Institutional Funds | Fair Value, Inputs, Level 1 | Fixed Income Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		11,671,000		11,599,000
Institutional Funds | Fair Value, Inputs, Level 2 | Equity Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Institutional Funds | Fair Value, Inputs, Level 2 | Fixed Income Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Institutional Funds | Fair Value, Inputs, Level 3 | Equity Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Institutional Funds | Fair Value, Inputs, Level 3 | Fixed Income Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		$ 0		$ 0
[1]	The institutional funds are invested in equity or fixed income securities, or a combination thereof. The investment objective of each fund is to produce returns in excess of, or commensurate with, its predefined index.
[2]	In the first quarter of 2016, the Company implemented ASU 2015-07, Fair Value Measurement (Topic 820) which eliminates the requirement to categorize investments in the fair value hierarchy if the fair value is measured at NAV per share (or its equivalent) using the practical expedient in the FASB’s fair value measurement guidance. The fair value amounts presented in the table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the statement of financial position. ASU 2015-07 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years.
[3]	This investment is a commercial real estate partnership that purchases land, develops limited infrastructure, and sells it for commercial development. The Company was restricted from selling its partnership interest during the life of the partnership, which spanned 7 years. Return of investment is realized as land is sold. The fair value of the limited partnership interest in real estate is based on the NAV of the partnership which reflects the appraised value of the land. The partnership term expired on June 30, 2016. Upon expiration, dissolution of the partnership commenced and, as a result, the general partner of the partnership is attempting to sell the remaining inventory as soon as possible at the highest pricing possible.

Employee Benefits (Changes i105

Employee Benefits (Changes in Fair Value Investment Real Estate - Other Postretirement Benefit Plans) (Details) - Other Postretirement Benefit Plan - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of prior year		$ 38,090		$ 41,358
Fair value of plan assets at end of year		39,115		38,090
Limited Partnership Interest in Real Estate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of prior year		1,610	[1],[2]	1,640
Unrealized gain (loss) in fair value		(154)		(30)
Sale of Land		(145)
Fair value of plan assets at end of year	[1],[2]	$ 1,311		$ 1,610
[1]	In the first quarter of 2016, the Company implemented ASU 2015-07, Fair Value Measurement (Topic 820) which eliminates the requirement to categorize investments in the fair value hierarchy if the fair value is measured at NAV per share (or its equivalent) using the practical expedient in the FASB’s fair value measurement guidance. The fair value amounts presented in the table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the statement of financial position. ASU 2015-07 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years.
[2]	This investment is a commercial real estate partnership that purchases land, develops limited infrastructure, and sells it for commercial development. The Company was restricted from selling its partnership interest during the life of the partnership, which spanned 7 years. Return of investment is realized as land is sold. The fair value of the limited partnership interest in real estate is based on the NAV of the partnership which reflects the appraised value of the land. The partnership term expired on June 30, 2016. Upon expiration, dissolution of the partnership commenced and, as a result, the general partner of the partnership is attempting to sell the remaining inventory as soon as possible at the highest pricing possible.

Employee Benefits (Expected 106

Employee Benefits (Expected Future Benefit Payments - Other Postretirement Benefit Plans) (Details) - Other Postretirement Benefit Plan $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	$ 1,500
2,017	2,622
2,018	2,880
2,019	3,057
2,020	3,320
2,021	3,510
2022-2026	$ 20,084

Employee Benefits (Details)

Employee Benefits (Details) $ in Millions	Apr. 02, 2014	Mar. 31, 2014	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Employee Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Number of Non-Qualified Retirement Plans			2
Defined benefit plans revisions effective date	Apr. 1, 2014
Short Term Incentive Plan Payout			$ 12.5	$ 10.5	$ 7.4
Retirement Income Plan
Employee Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined benefit plans revisions effective date	Apr. 1, 2014
Pension benefit earned by employee is frozen, date.		Mar. 31, 2014
Retirement Income Plan | Years Of Service
Employee Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Years of Service Requisite			1

Franchises and Significant C108

Franchises and Significant Customers (Details)	12 Months Ended
	Dec. 31, 2016MW
El Paso
Franchises and Significant Customers [Line Items]
Preceded Franchise Fee Percent	3.25%
Percentage of Revenue Additional Franchise Fees, Restricted	0.75%
Retail Electric Service Contract, Expiration Date	Jul. 31, 2030
Las Cruces
Franchises and Significant Customers [Line Items]
Retail Electric Service Contract, Expiration Date	Apr. 30, 2009
August 1, 2010 through Present | El Paso
Franchises and Significant Customers [Line Items]
Franchise Fee, Percent	4.00%
February 1, 2000 through Present | Las Cruces
Franchises and Significant Customers [Line Items]
Franchise Fee, Percent	2.00%
Sales Revenue, Services, Net | Military Bases
Franchises and Significant Customers [Line Items]
Concentration Risk, Percentage	2.80%
Holloman Air Force Base Solar Facility
Franchises and Significant Customers [Line Items]
Electric capacity	5

Financial Instruments and In109

Financial Instruments and Investments (Carrying Amount and Fair Value Amounts) (Details) - USD ($) $ in Thousands		Dec. 31, 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]	$ 1,360,230	$ 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]	190,775	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]	993,086	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]	94,795	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]	81,574	141,738
Estimate of Fair Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		1,499,532	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		206,818	212,624
Estimate of Fair Value Measurement | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		1,112,285	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]	98,855	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]	$ 81,574	$ 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 December 31, 2016 and December 31, 2015, is funded through the $95 million RGRT Senior Notes and $37.6 million and $33.7 million, respectively under the RCF. As of December 31, 2016, $44.0 million was outstanding under the RCF for working capital or general corporate purposes. As of December 31, 2015, $108.0 million amount 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 period reflecting current market rates. Consequently, the carrying value approximates fair value.

Financial Instruments And In110

Financial Instruments And Investments (Long-Term Debt And Short-Term Borrowings - Narratives) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	May 01, 2005
Financial Instruments and Investments [Line Items]
Interest Rate Cash Flow Hedge Loss to be Reclassified During Next 12 Months, Net	$ 500
Decommissioning Fund Investments	255,708	$ 239,035
Accounting Standards Update 2015-03 [Member]
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	37,600	33,700
Working Capital and General Purpose
Financial Instruments and Investments [Line Items]
Line of Credit Facility, Amount Outstanding	$ 44,000	$ 108,000
Senior Notes | 6.00% Senior Notes, Net of Discount, due 2035
Financial Instruments and Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.00%	6.00%	6.00%
RGRT Senior Notes
Financial Instruments and Investments [Line Items]
Long-term Debt, Gross	$ 95,000	$ 95,000

Financial Instruments And In111

Financial Instruments And Investments (Marketable Securities Fair Value And Unrealized Losses) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)securities		Dec. 31, 2015USD ($)securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value, Less than 12 Months	$ 86,509	[1]	$ 73,859	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(1,844)	[1]	(2,401)	[2]
Marketable Securities Fair Value 12 Months or Longer	24,571	[1]	25,080	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(1,401)	[1]	(1,344)	[2]
Marketable Securities Fair Value, Total	111,080	[1]	98,939	[2]
Marketable Securities Unrealized Losses, Total	$ (3,245)	[1]	$ (3,745)	[2]
Number of securities | securities	152		133
Debt Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value, Less than 12 Months	$ 60,804	[1]	$ 47,821	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(1,567)	[1]	(1,289)	[2]
Marketable Securities Fair Value 12 Months or Longer	24,571	[1]	25,080	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(1,401)	[1]	(1,344)	[2]
Marketable Securities Fair Value, Total	85,375	[1]	72,901	[2]
Marketable Securities Unrealized Losses, Total	(2,968)	[1]	(2,633)	[2]
Collateralized Mortgage Backed Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value, Less than 12 Months	11,582	[1]	9,383	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(239)	[1]	(97)	[2]
Marketable Securities Fair Value 12 Months or Longer	436	[1]	1,113	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(22)	[1]	(47)	[2]
Marketable Securities Fair Value, Total	12,018	[1]	10,496	[2]
Marketable Securities Unrealized Losses, Total	(261)	[1]	(144)	[2]
U.S. Government Bonds
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value, Less than 12 Months	31,655	[1]	24,094	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(762)	[1]	(310)	[2]
Marketable Securities Fair Value 12 Months or Longer	17,976	[1]	14,272	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(835)	[1]	(623)	[2]
Marketable Securities Fair Value, Total	49,631	[1]	38,366	[2]
Marketable Securities Unrealized Losses, Total	(1,597)	[1]	(933)	[2]
Municipal Bonds
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value, Less than 12 Months	9,596	[1]	8,286	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(394)	[1]	(160)	[2]
Marketable Securities Fair Value 12 Months or Longer	4,067	[1]	7,388	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(372)	[1]	(446)	[2]
Marketable Securities Fair Value, Total	13,663	[1]	15,674	[2]
Marketable Securities Unrealized Losses, Total	(766)	[1]	(606)	[2]
Corporate Debt Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value, Less than 12 Months	7,971	[1]	6,058	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(172)	[1]	(722)	[2]
Marketable Securities Fair Value 12 Months or Longer	2,092	[1]	2,307	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(172)	[1]	(228)	[2]
Marketable Securities Fair Value, Total	10,063	[1]	8,365	[2]
Marketable Securities Unrealized Losses, Total	(344)	[1]	(950)	[2]
Equity Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value, Less than 12 Months	2,760	[1]	3,584	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(167)	[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	2,760	[1]	3,584	[2]
Marketable Securities Unrealized Losses, Total	(167)	[1]	(344)	[2]
Institutional Funds-International Equity
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value, Less than 12 Months	22,945	[1]	22,454	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(110)	[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	22,945	[1]	22,454	[2]
Marketable Securities Unrealized Losses, Total	$ (110)	[1]	$ (768)	[2]
[1]	Includes approximately 152 securities.
[2]	Includes approximately 133 securities.

Financial Instruments And In112

Financial Instruments And Investments (Unrealized Holding Losses Included In Pre-Tax Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financial Instruments And Investments [Abstract]
Unrealized losses included in pre-tax income	$ (352)	$ (338)	$ 0

Financial Instruments And In113

Financial Instruments And Investments (Marketable Securities Fair Value and Unrecognized Gross Unrealized Gains) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Gross Unrealized Gain	$ 38,667	$ 38,366
Marketable Securities Fair Value, Total	144,628	140,096
Debt Securities
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	34,498	40,403
Available-for-sale Securities, Gross Unrealized Gain	1,256	1,274
Collateralized Mortgage Backed Securities
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	7,430	9,589
Available-for-sale Securities, Gross Unrealized Gain	319	438
U.S. Government Bonds
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	12,237	12,033
Available-for-sale Securities, Gross Unrealized Gain	138	136
Municipal Bonds
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	2,481	8,671
Available-for-sale Securities, Gross Unrealized Gain	144	332
Corporate Debt Securities
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	12,350	10,110
Available-for-sale Securities, Gross Unrealized Gain	655	368
Equity Securities
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	61,884	72,636
Available-for-sale Securities, Gross Unrealized Gain	34,066	37,001
Equity Mutual Funds
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Unrealized Gain Position, Fair Value	42,244	18,853
Available-for-sale Securities, Gross Unrealized Gain	3,345	91
Cash
Financial Instruments and Investments [Line Items]
Available-for-sale Securities, Gross Unrealized Gain	0	0
Cash | Held in trust Decommissioning Fund Investment
Financial Instruments and Investments [Line Items]
Cash	$ 6,002	$ 8,204

Financial Instruments And In114

Financial Instruments And Investments (Contractual Year For Maturity Of Available-For-Sale Securities ) (Details) $ in Thousands	Dec. 31, 2016USD ($)
Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Total	$ 16,144
2,017	990
2018 through 2021	6,253
2022 through 2026	8,139
2027 and Beyond	762
Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Total	22,413
2,017	0
2018 through 2021	8,664
2022 through 2026	6,090
2027 and Beyond	7,659
U.S. Government Bonds
Schedule of Available-for-sale Securities [Line Items]
Total	61,868
2,017	14,272
2018 through 2021	22,495
2022 through 2026	14,786
2027 and Beyond	10,315
Collateralized Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Total	19,448
2,017	0
2018 through 2021	5
2022 through 2026	390
2027 and Beyond	$ 19,053

Financial Instruments And In115

Financial Instruments And Investments (Sale Of Securities And The Related Effects On Pre-Tax Income ) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investment [Line Items]
Proceeds from sales of available-for-sale securities	$ 91,268	$ 102,567	$ 108,311
Gross realized gains included in pre-tax income	9,212	12,379	7,858
Gross realized losses included in pre-tax income	(1,220)	(927)	(508)
Gross unrealized losses included in pre-tax income	(352)	(338)	0
Net gains (losses) in pre-tax income	7,640	11,114	7,350
Net unrealized holding gains (losses) included in accumulated other comprehensive income	8,444	(2,906)	10,827
Net (gains) losses reclassified out of accumulated other comprehensive income	(7,640)	(11,114)	(7,350)
Net gains (losses) in other comprehensive income	$ 804	$ (14,020)	$ 3,477

Financial Instruments And In116

Financial Instruments And Investments (Company's Decommissioning Trust Funds And Investments In Debt Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	$ 255,708	$ 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	197,703	176,130
Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	58,005	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	1,421	1,543	$ 1,653
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	1,421	1,543
Debt Securities | Decommisioning Fund Investments
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	119,873	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	61,868	50,399
Debt Securities | Decommisioning Fund Investments | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Available-for-sale Securities	58,005	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	61,868	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	61,868	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	19,448	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	19,448	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	16,144	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	16,144	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	22,413	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	22,413	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	64,644	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	64,644	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	42,244	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	42,244	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	22,945	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	22,945	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 | Held in trust Decommissioning Fund Investment
Financial Instruments and Investments [Line Items]
Cash	6,002	8,204
Cash | Held in trust Decommissioning Fund Investment | Quoted Prices In Active Markets For Identical Assets (Level 1)
Financial Instruments and Investments [Line Items]
Cash	6,002	8,204
Cash | Held in trust Decommissioning Fund Investment | Significant Other Observable Inputs (Level 2)
Financial Instruments and Investments [Line Items]
Cash	0	0
Cash | Held in trust Decommissioning Fund Investment | Significant Unobservable Inputs (Level 3)
Financial Instruments and Investments [Line Items]
Cash	$ 0	$ 0

Financial Instruments and In117

Financial Instruments and Investments (Reconciliation) (Details) - Debt Securities - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Fair Value in Investment in Debt Securities [Roll Forward]
Balance at January 1		$ 1,543	$ 1,653
Net unrealized gains (losses) in fair value recognized in income on debt securities still held	[1]	(122)	(110)
Balance at December 31		$ 1,421	$ 1,543
[1]	These amounts are reflected in the Company's statements of operations as investment and interest income.

Financial Instruments and In118

Financial Instruments and Investments Transfers Between Levels (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value, Assets, Level 1 to Level 2 Transfers, Description	no	no
Fair Value, Assets, Level 2 to Level 1 Transfers, Description	no	no
Fair Value, Assets, Level 3 Purchases, (Sales), Issuances, (Settlements)	$ 0	$ 0

Supplemental Statements of C119

Supplemental Statements of Cash Flows Disclosures Supplemental Statements of Cash Flows Disclosures (Details) - USD ($) $ in Thousands		Jul. 06, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Cash Flow Information [Abstract]
Interest on long-term debt and borrowing under the revolving credit facility			$ 69,990	$ 62,297	$ 54,792
Income taxes, net of refund			2,328	1,000	6,876
Sale of Interest in Four Corners Generating Station	[1]		27,720	0	0
Changes in accrued plant additions			4,789	(6,660)	7,314
Site Contingency [Line Items]
Asset Retirement Obligation			81,800	81,621	74,577	$ 65,214
Proceeds from sale of property, plant, and equipment			4,841	721	2,395
Four Corners Generating Station
Site Contingency [Line Items]
Property, Plant and Equipment, Disposals		$ 32,000
Asset Retirement Obligation		7,000
Mine Reclamation and Closing 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
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants of restricted shares of common stock			$ 1,236	$ 1,567	$ 3,025
[1]	The Company sold its interest in Four Corners for approximately $32.0 million based on the book value as defined in the Purchase and Sale Agreement. The sales price was adjusted downward by $7.0 million and $19.5 million to reflect APS's affiliate assumption of the Company's obligation to pay for future plant decommissioning and mine reclamation expense, respectively. The sales price was also adjusted downward by approximately $1.3 million for closing adjustments and other assets and liabilities assumed by APS's affiliate. At the closing of the sale, the Company received approximately $4.2 million in cash, subject to post-closing adjustments.

Selected Quarterly Financial120

Selected Quarterly Financial Data (Unaudited) Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2016		Sep. 30, 2016	[2]	Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Selected Quarterly Financial Data
Operating revenues	$ 188,037	[1]	$ 323,225	[1]	$ 217,865	[1]	$ 157,809	[1]	$ 176,902	[1]	$ 289,713	[1]	$ 219,508	[1]	$ 163,746	[1]	$ 886,936	$ 849,869	$ 917,525
Operating income (loss)	20,470		129,857		44,697		(163)		8,312		88,047		41,872		7,960		194,861	146,191	151,163
Net income	$ 5,656		$ 74,636		$ 22,284		$ (5,808)		$ 648		$ 56,740		$ 21,072		$ 3,458		$ 96,768	$ 81,918	$ 91,428
Basic earnings per share:
Net income (loss)	$ 0.14		$ 1.84		$ 0.55		$ (0.14)		$ 0.02		$ 1.40		$ 0.52		$ 0.09		$ 2.390	$ 2.030	$ 2.270
Diluted earnings per share:
Net income (loss)	0.14		1.84		0.55		(0.14)		0.02		1.40		0.52		0.09		2.390	2.030	2.270
Dividends declared per share of common stock	$ 0.310		$ 0.310		$ 0.310		$ 0.295		$ 0.295		$ 0.295		$ 0.295		$ 0.280		$ 1.225	$ 1.165	$ 1.105
[1]	Operating revenues are seasonal in nature, with the peak sales periods generally occurring during the summer months. Comparisons among quarters of a year may not represent overall trends and changes in operations.(2)For financial reporting purposes, the Company deferred any recognition of the Company's request in its 2015 Texas Retail Rate Case until it received the PUCT Final Order on August 25, 2016. Accordingly, it reported in the third quarter of 2016 the cumulative effect of the PUCT Final Order which related back to January 12, 2016. See Part II, Item 8, Financial Statements and Supplementary Data, Note C.
[2]	For financial reporting purposes, the Company deferred any recognition of the Company's request in its 2015 Texas Retail Rate Case until it received the PUCT Final Order on August 25, 2016. Accordingly, it reported in the third quarter of 2016 the cumulative effect of the PUCT Final Order which related back to January 12, 2016. See Part II, Item 8, Financial Statements and Supplementary Data, Note C.