OVERVIEW AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
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. 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, 2017, which was filed with the Securities and Exchange Commission (SEC) on December 6, 2017. References to Fiscal 2018 and Fiscal 2017 used throughout this report shall mean our fiscal years ended September 30, 2018 and 2017, 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, warranty accruals and income taxes. The amounts recorded for warranties, legal, income taxes, impairment of long-lived assets (when applicable) 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 routinely change as new events occur, additional information becomes available or operating environments change. Actual results may differ from our prior 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 standard is 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. We plan to use the modified retrospective basis upon adoption. As part of our implementation process, we are evaluating a sample of contracts to identity potential impacts of the standard on our current accounting policies and disclosures. We will update our accounting policies and procedures and determine the impact from this new standard on our contracts outstanding as of October 1, 2018. While we are still evaluating the potential impact of this standard on our financial statements, we believe accounting for variable consideration, cancellations for convenience clauses and the number of performance obligations contained in each contract could have the greatest significance. The materiality of this guidance on our financial statements will be determined in large part by the contracts that are in progress as of the adoption date. 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. We have adopted this topic prospectively in Fiscal 2018 and our statement of financial position reflects this reclassification. We have not retrospectively adjusted prior periods. 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 topic 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 still evaluating the potential impact of this topic on our financial statements. In November 2016, the FASB issued a new topic on the statement of cash flows that changes the presentation of restricted cash and cash equivalents on the statement of cash flows. Restricted cash and restricted cash equivalents will be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. This topic is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, which would be our fiscal year ending September 30, 2019. We are still evaluating this new standard, but we do not expect it to have a material impact on our consolidated financial position or results of operations. In May 2017, the FASB issued a new topic on modification accounting with regards to stock based compensation. This new topic clarifies when a change to the terms or conditions of a share-based payment award should be accounted for as a modification. An entity should account for the effects of a modification unless the fair value, vesting conditions and classification, as an equity instrument or a liability instrument, of the modified award are the same before and after a change to the terms or conditions of the share-based payment award. This topic is effective for annual reporting periods beginning after December 15, 2017, which is our fiscal year ending September 30, 2019. We do not expect this topic to have a material impact on our consolidated financial position or results of operations.