Overview and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Overview	Overview Powell Industries, Inc. (we, us, our, Powell or the Company) was incorporated in the state of Delaware in 2004 as a successor to a Nevada company incorporated in 1968. The Nevada corporation was the successor to a company founded by William E. Powell in 1947, which merged into the Company in 1977. Our major subsidiaries, all of which are wholly owned, include: Powell Electrical Systems, Inc.; Powell (UK) Limited; Powell Canada Inc. and Powell Industries International, B.V. We develop, design, manufacture and service custom-engineered equipment and systems for the distribution, control and monitoring of electrical energy. Headquartered in Houston, Texas, we serve the oil and gas refining, offshore oil and gas production, petrochemical, pipeline, terminal, mining and metals, light rail traction power, electric utility, pulp and paper and other industrial markets.
Basis of Presentation	Basis of Presentation These unaudited condensed consolidated financial statements include the accounts of Powell and its wholly-owned subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation. These unaudited condensed consolidated financial statements have been prepared in accordance with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X for interim financial information. Certain information and footnote disclosures, normally included in annual financial statements prepared in accordance with accounting principles generally accepted in the United States (U.S. GAAP), have been condensed or omitted pursuant to those rules and regulations. In the opinion of management, all adjustments, consisting only of normal recurring adjustments, necessary to fairly state the financial position, results of operations and cash flows with respect to the interim condensed consolidated financial statements have been included. The results of operations for the interim periods are not necessarily indicative of the results for the entire fiscal year. We believe that these financial statements contain all adjustments necessary so that they are not misleading. The year-end balance sheet data was derived from audited financial statements, but does not include all disclosures required by U.S. GAAP. These unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto of Powell and its subsidiaries included in Powell’s Annual Report on Form 10-K for the year ended September 30, 2016, which was filed with the Securities and Exchange Commission (SEC) on December 7, 2016. References to Fiscal 2017, Fiscal 2016 and Fiscal 2015 used throughout this report shall mean our fiscal years ended September 30, 2017, 2016 and 2015, respectively.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying footnotes. The most significant estimates used in our condensed consolidated financial statements affect revenue and cost recognition for construction contracts, the allowance for doubtful accounts, provision for excess and obsolete inventory, self-insurance, warranty accruals, liquidated damages and income taxes. The amounts recorded for insurance claims, warranties, legal, liquidated damages, income taxes and other contingent liabilities require judgments regarding the amount of expenses that will ultimately be incurred. We base our estimates on historical experience and on various other assumptions, as well as the specific circumstances surrounding these contingent liabilities, in evaluating the amount of liability that should be recorded. Additionally, the recognition of deferred tax assets requires estimates related to future income and other assumptions regarding timing and future profitability. Estimates may change as new events occur, additional information becomes available or operating environments change. Actual results may differ from our estimates.
New Accounting Standards	New Accounting Standards In May 2014, the Financial Accounting Standards Board (FASB) issued a new standard on revenue recognition that supersedes previously issued revenue recognition guidance. This standard provides a five-step approach to be applied to all contracts with customers and requires expanded disclosures about the nature, amount, timing and uncertainty of revenue (and the related cash flows) arising from customer contracts, significant judgments and changes in judgments used in applying the revenue model and the assets recognized from costs incurred to obtain or fulfill a contract. This guidance is now effective for fiscal years, and interim periods within those years, beginning after December 15, 2017, which would be our fiscal year ending September 30, 2019. The standard permits the use of either the full retrospective or modified retrospective transition method; therefore, we are evaluating the effect that this new guidance will have on our consolidated financial statements and related disclosures. We have not yet selected a transition method nor have we determined the effect of the standard on our ongoing financial reporting. In August 2014, the FASB issued guidance to address the diversity in practice in determining when there is substantial doubt about an entity’s ability to continue as a going concern and when and how an entity must disclose certain relevant conditions and events. This update requires an entity to evaluate whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the entity’s ability to continue as a going concern for a period of one year after the date that the financial statements are issued (or available to be issued). If such conditions or events exist, an entity should disclose that there is substantial doubt about the entity’s ability to continue as a going concern for a period of one year after the date that the financial statements are issued (or available to be issued), along with the principal conditions or events that raise substantial doubt, management’s evaluation of the significance of those conditions or events in relation to the entity’s ability to meet its obligations and management’s plans that are intended to mitigate those conditions or events. This guidance impacts the disclosure and presentation of any substantial doubt about our ability to continue as a going concern, if such substantial doubt were to exist. This guidance is effective for our first quarter ended December 31, 2016 and does not have an impact on disclosures in our condensed consolidated financial statements. In November 2015, the FASB issued an amendment to the topic regarding income taxes which requires an entity to separate deferred income tax liabilities and assets into current and noncurrent amounts in the statement of financial position. Deferred tax liabilities and assets are classified as current or noncurrent based on the classification of the related asset or liability for financial reporting. Deferred tax liabilities and assets that are not related to an asset or liability for financial reporting are classified according to the expected reversal date of the temporary difference. To simplify the presentation of deferred income taxes, the amendments require that deferred income tax liabilities and assets be classified as noncurrent in a classified statement of financial position. This amendment is effective for annual reporting periods beginning after December 15, 2016, which would be our fiscal year ending September 30, 2018. We have no plans for early adoption. The adoption of this guidance is not expected to have a material impact on our consolidated financial position or results of operations. In February 2016, the FASB issued a new topic on leases which requires lessees to recognize lease assets and lease liabilities on the balance sheet for all leases with terms longer than twelve months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. A modified retrospective transition approach is required for lessees for capital and operating leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, with certain practical expedients available. The new standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. This would be our fiscal year ending September 30, 2020. We are currently evaluating the impact of our pending adoption of the new standard, but do not expect it to have a material impact on our consolidated financial position or results of operations. In March 2016, the FASB issued new guidance on stock-based compensation, which includes amendments to existing guidance for employee share-based payment accounting. We elected to early adopt this new guidance in the first quarter of Fiscal 2017. Beginning with this quarter, stock-based compensation excess tax benefits or deficiencies are reflected in the Condensed Consolidated Statement of Operations as a component of income taxes, whereas they were previously recorded in additional paid in capital in the Condensed Consolidated Statement of Stockholders’ Equity. Additionally, we will now present excess tax benefits as an operating activity in the Condensed Consolidated Statements of Cash Flows, and prior periods will be adjusted accordingly. Finally, we will continue to account for forfeitures as they occur, rather than estimate expected forfeitures.