Principles Of Preparation (Policy)	3 Months Ended
Principles Of Preparation (Policy)	Mar. 31, 2016
Accounting Policies [Abstract]
Use of Estimates, Policy	Use of Estimates. The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. The Company evaluates its estimates on an on-going basis, including those related to depreciation, unbilled revenue, income taxes, fuel costs, pension and other post-retirement obligations and asset retirement obligations ("ARO"). Actual results could differ from those estimates.
Revenue Recognition, Policy	Revenues. Revenues related to the sale of electricity are generally recorded when service is provided or electricity is delivered to customers. The billing of electricity sales to retail customers is based on the reading of their meters, which occurs on a systematic basis throughout the month. Unbilled revenues are recorded for estimated amounts of energy delivered in the period following the 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 $17.9 million at March 31, 2016 and $21.7 million at December 31, 2015. The Company presents revenues net of sales taxes in its statements of operations.
New Accounting Standards, Policy	New Accounting Standards. In April 2015, the FASB issued ASU 2015-03, Interest - Imputation of Interest (Topic 715) to simplify the presentation of debt issuance costs. ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by this ASU. ASU 2015-03 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. In August 2015, the FASB issued ASU 2015-15, Interest - Imputation of Interest (Subtopic 835-30), to provide further clarification to ASU 2015-03 as it relates to the presentation and subsequent measurement of debt issuance costs associated with line of credit arrangements. The Company implemented ASU 2015-03 and ASU 2015-15 in the first quarter of 2016, retrospectively to all prior periods presented in the Company's financial statements. The implementation of ASU 2015-03 did not have a material impact on the Company's results of operations. See Note J. In May 2015, the FASB issued ASU 2015-07, Fair Value Measurement (Topic 820) to eliminate the requirement to categorize investments in the fair value hierarchy if the fair value is measured at net asset value ("NAV") per share (or its equivalent) using the practical expedient in the FASB’s fair value measurement guidance. Reporting entities must still provide sufficient information to enable users to reconcile total investments in the fair value hierarchy and total investments measured at fair value in the financial statements. Additionally, the scope of current disclosure requirements for investments eligible to be measured at NAV will be limited to investments to which the practical expedient is applied. This ASU is effective in fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. The ASU requires retrospective application. The Company implemented ASU 2015-07 in the first quarter of 2016, retrospectively to all prior periods presented in the Company's fair value disclosures. This guidance required a revision of the fair value disclosures but did not impact the Company's financial statements. The implementation of ASU 2015-07 did not have a material impact on the Company's results of operations. See Note J. In November 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes to simplify the presentation of deferred income taxes. ASU 2015-17 requires that deferred tax liabilities and assets be classified as noncurrent in a classified statement of financial position. ASU 2015-17 can be applied prospectively or retrospectively and is effective for financial statements issued for annual periods beginning after December 15, 2016 and interim periods within those annual periods and early adoption is permitted. The Company elected to early adopt ASU 2015-17 retrospectively in the first quarter of 2016. The implementation of ASU 2015-17 did not have a material impact on the Company's results of operations. See Note F. In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2014-09, Revenue from Contracts with Customers (Topic 606) to provide a framework that replaces the existing revenue recognition guidance. ASU 2014-09 is the result of a joint effort by the FASB and the International Accounting Standards Board intended to clarify the principles for recognizing revenue and to develop a common revenue standard for U.S. Generally Accepted Accounting Principles ("GAAP") and International Financial Reporting Standards. ASU 2014-09 provides that an entity should recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. ASU 2014-09 was originally intended to be effective for annual periods and interim periods within that reporting period beginning after December 15, 2016, for public business entities. In August 2015, FASB issued ASU 2015-14 to defer the effective date of ASU 2014-09 for all entities by one year. Public business entities will apply the guidance in ASU 2014-09 to annual reporting periods beginning after December 15, 2017 and interim periods within that reporting period. In March 2016, the FASB issued ASU 2016-08 to clarify the implementation guidance on principal versus agent consideration. In April 2016, the FASB issued ASU 2016-10 to clarify the implementation guidance on identifying performance obligations and licensing. Early adoption of ASU 2014-09 is permitted after December 15, 2016. The Company has not selected a transition method and is currently assessing the future impact of this ASU. In January 2016, the FASB issued ASU 2016-01, Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Liabilities to enhance the reporting model for financial instruments by addressing certain aspects of recognition, measurement, presentation, and disclosure. ASU 2016-01 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 unless the investments qualify for the new practicability exception. The guidance for classifying and measuring investments in debt securities and loans are not changed by this ASU, but requires entities to record changes in instrument-specific credit risk for financial liabilities measured under the fair value option in other comprehensive income. Financial assets and financial liabilities must be separately presented by measurement category and form of financial asset on the balance sheet or in the accompanying notes to the financial statements. ASU 2016-01 clarifies the need for a valuation allowance on a deferred tax asset related to available-for-sale securities in combination with the entity's other deferred tax assets. The standard includes a requirement that businesses must report changes in the fair value of their own liabilities in other comprehensive income instead of earnings, and this is the only provision of the update for which the FASB is permitting early adoption. The remaining provisions of this ASU become effective for public companies for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The Company is currently assessing the future impact of this ASU. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) to increase transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and requiring qualitative and quantitative disclosures on leasing agreements. ASU 2016-02 maintains a distinction between finance leases and operating leases similar to the distinction under previous leases guidance for capital leases and operating leases. The impact of leases reported in the Company's operating results and statement of cash flows are expected to be similar to previous GAAP. ASU 2016-02 requires the recognition in the statement of financial position, by the lessee, of a liability to make lease payments (the lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term. How leases are recorded in regard to financial position represents a significant change from previous GAAP. The lessee is permitted to make an accounting policy election to not recognize lease assets and lease liabilities for short-term leases. Implementation of the standard for public companies will be required for annual reporting periods beginning after December 15, 2018 and interim periods within that reporting period. Early adoption of ASU 2016-02 is permitted for all entities. Adoption of the new lease accounting standard will require the Company to apply the new standard to the earliest period using a modified retrospective approach. The Company is currently assessing the future impact of this ASU. In March 2016, the FASB issued ASU 2016-09, Compensation – Stock Compensation (Topic 718) Improvements to Employee Share-Based Payment Accounting to simplify the accounting for share-based payment transactions, including the income tax consequences, classification of awards either as equity or liabilities, and classification on the statements of cash flows. This ASU is effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods. Early adoption is permitted. The Company is currently assessing the future impact of this ASU.
Reclassification, Policy	Reclassification. Certain amounts in the financial statements for 2015 have been reclassified to conform with the 2016 presentation. The Company implemented ASU 2015-03 and ASU 2015-17 in the first quarter of 2016, retrospectively to all periods presented in the Company's financial statements. See Note J and Note F, respectively.

Disclosure of accounting policy for revenue recognition. If the entity has different policies for different types of revenue transactions, the policy for each material type of transaction is generally disclosed. If a sales transaction has multiple element arrangements (for example, delivery of multiple products, services or the rights to use assets) the disclosure may indicate the accounting policy for each unit of accounting as well as how units of accounting are determined and valued. The disclosure may encompass important judgment as to appropriateness of principles related to recognition of revenue. The disclosure also may indicate the entity's treatment of any unearned or deferred revenue that arises from the transaction.