OVERVIEW AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
	Mar. 31, 2019
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, 2018, which was filed with the Securities and Exchange Commission (SEC) on December 12, 2018. References to Fiscal 2019 and Fiscal 2018 used throughout this report shall mean our fiscal years ended September 30, 2019 and 2018, 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 recognition and estimated cost recognition on our customer 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 because the ultimate realization of net deferred tax assets is dependent on the generation of future taxable income during the periods in which temporary differences become deductible. 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. Effective October 1, 2018, we adopted this standard using the modified retrospective basis. After evaluating the impact of this new standard on contracts outstanding as of October 1, 2018, we determined that no adjustment to retained earnings was necessary. See Note D for further discussion of revenue. 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. In Fiscal 2018, we acquired new lease software designed to assist with our compliance of this new topic. We are still evaluating the impact this new topic will have on our consolidated financial position and results of operations. 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 is to 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. We adopted this topic in Fiscal 2019 and our Condensed Consolidated Cash Flow Statements for all periods reflect this presentation. 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. We adopted this topic in Fiscal 2019 and it has not had a material impact on our consolidated financial position or results of operations.
Revenue Recognition	On October 1, 2018, we adopted the new revenue recognition standard using the modified retrospective transition method. We applied the guidance to customer contracts which were not substantially complete at that time and we determined that no adjustment to retained earnings was necessary. Financial results for reporting periods after October 1, 2018 are reported under the new guidance; however financial results for prior periods were not adjusted and will continue to be presented in accordance with the previous guidance. Revenue Recognition The majority of our revenues are generated from the manufacturing of custom engineered products and systems under long-term fixed price contracts under which we agree to manufacture various products such as traditional and arc-resistant distribution switchgear and control gear, medium-voltage circuit breakers, monitoring and control communications systems, motor control centers and bus duct systems. These products may be sold separately as an engineered solution, but are typically integrated into custom-built enclosures which we also build. These enclosures are referred to as power control room substations (PCRs®), custom-engineered modules or electrical houses (E-Houses). Some contracts may also include the installation and the commissioning of these enclosures. Revenue from these contracts is generally recognized over time utilizing the cost to cost method to measure the extent of progress toward the completion of the performance obligation and the recognition of revenue over time. We believe that this method is the most accurate representation of our performance because it directly measures the value of the services transferred to the customer over time as we incur costs on our contracts. Contract costs include all direct materials, labor, and indirect costs related to contract performance which may include indirect labor, supplies, tools, repairs and depreciation costs. We also have contracts to provide value-added services such as field service inspection, installation, commissioning, modification and repair, as well as retrofit and retrofill components for existing systems. As a practical expedient, if the service contract terms give us the right to invoice the customer for an amount that corresponds directly with the value of our performance completed to date (i.e., a service contract in which we bill a fixed amount for each hour of service provided), then we recognize revenue over time in each reporting period corresponding to the amount with which we have the right to invoice. Our performance obligations are satisfied as the work progresses. Revenues from our custom-engineered products and value-added services transferred to customers over time accounted for approximately 93% of total revenues for both the three and six months ended March 31, 2019. We also have sales orders for spare parts and replacement circuit breakers for switchgear that are obsolete or that are no longer produced by the original manufacturer. Revenues from these sales orders are recognized at a point in time when we fulfill our performance obligation to the customer which is typically upon shipment. Revenue related to sales orders represents approximately 7% of total revenues for both the three and six months ended March 31, 2019. Additionally, some contracts may contain a cancellation clause that could limit the amount of revenue we are able to recognize over time. In these instances, revenue and costs associated with these contracts are deferred and recognized at a point in time when the performance obligation is fulfilled. Selling and administrative costs incurred in relation to obtaining a contract are typically expensed as incurred. We periodically utilize a third-party sales agent to obtain a contract and will pay a commission to that agent. We record the full commission liability to the third-party sales agents at the order date, with a corresponding deferred asset. As the project progresses, we record commission expense based on percentage of completion rates that correlate to the project and reduce the deferred asset. Once we have been paid by the customer, we pay the commission and the deferred liability is reduced Variable Consideration It is common for our long-term contracts to contain variable consideration that can either increase or decrease the transaction price. Due to the nature of our contracts, estimating total cost and revenue can be complex and subject to variability due to change orders, back charges, spare parts, early completion bonuses, customer allowances and liquidated damages. We estimate the amount of variable consideration based on the expected value method, which is the sum of probability-weighted amount, or the most likely amount method which uses various factors including experience with similar transactions and assessment of our anticipated performance. Variable consideration is included in the transaction price if legally enforceable and to the extent it is probable that a significant reversal of cumulative revenue recognized will not occur once the uncertainty associated with the variable consideration is resolved. Contract Modifications Contracts may be modified for changes in contract specifications and requirements. We consider contract modifications to exist when the modification either creates new or changes the enforceable rights and obligations under the contract. Most of our contract modifications are for goods and services that are not distinct from the existing performance obligation. Contract modifications result in a cumulative catch up adjustment to revenue based on our measure of progress for the performance obligation. Contract Balances The timing of revenue recognition, billings and cash collections affects accounts receivable, costs and estimated earnings in excess of billings on uncompleted contracts (contract assets) and billings in excess of costs and estimated earnings on uncompleted contracts (contract liabilities) in our Condensed Consolidated Balance Sheet. Contract assets, previously referred to as costs and estimated earnings in excess of billings on uncompleted contracts, are recorded when revenues are recognized in excess of amounts billed for fixed-price contracts as determined by the billing milestone schedule. Contract assets are transferred to accounts receivables when billing milestones have been met or we have an unconditional right to payment. Contract liabilities, previously referred to as billings in excess of costs and estimated earnings on uncompleted contracts, typically represent advance payments from contractual billing milestones and billings in excess of revenue recognized. It is unusual to have advanced milestone payments with a term greater than one year, which could represent a financing component on the contract. Our contract assets and liabilities are reported in a net position on a contract-by-contract basis at the end of each reporting period and are generally classified as current. The timing of our invoice process is typically dependent on the completion of certain milestones and contract terms and subject to agreement by our customer. Payment is typically expected within 30 days of invoice. Any uncollected invoiced amounts for our performance obligations recognized over time, including contract retentions, are recorded as accounts receivable in the Condensed Consolidated Balance Sheets. Certain contracts contain retention provisions that become due upon completion of contractual requirements. Contract Estimates Actual revenues and project costs may vary from previous estimates due to changes in a variety of factors. The cost estimation process is based upon the professional knowledge and experience of our engineers, project managers and financial professionals. Factors that are considered in estimating the work to be completed and ultimate contract recovery include the availability and productivity of labor, the nature and complexity of the work to be performed, the availability of materials, and the effect of any delays on our project performance. We periodically review our job performance, job conditions, estimated profitability and final contract settlements, including our estimate of total costs and make revisions to costs and income in the period in which the revisions are probable and reasonably estimable. Whenever revisions of estimated contract costs and contract values indicate that the contract costs will exceed estimated revenues, thus creating a loss, a provision for the total estimated loss is recorded in that period. Performance Obligations A performance obligation is a promise in a contract or with a customer to transfer a distinct good or service. A contract’s transaction price is allocated to each distinct performance obligation and recognized as revenue as the performance obligations are satisfied. To determine the proper revenue recognition for contracts, we evaluate whether a contract should be accounted for as more than one performance obligation or, less commonly, whether two or more contracts should be combined and accounted for as one performance obligation. This evaluation of performance obligations requires significant judgement. The majority of our contracts have a single performance obligation where multiple engineered products and services are combined into a single custom engineered solution. Our contracts generally include a standard assurance warranty that typically ends eighteen months after shipment. Occasionally, we provide service-type warranties that will extend the warranty period. These extended warranties qualify as a separate performance obligation. If we determine during the evaluation of the contract that there are multiple performance obligations, we allocate the transaction price to each performance obligation using our best estimate of the standalone selling price of each distinct good or service in the contract. Remaining unsatisfied performance obligations, which we refer to as backlog, represent the estimated transaction price for goods and services for which we have a material right but work has not been performed.