Basis of Presentation and Preparation	12 Months Ended
Oct. 01, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Preparation	Basis of Presentation and Preparation Principles of Consolidation and Presentation. The consolidated financial statements include our accounts and those of joint ventures of which we are the primary beneficiary. All significant intercompany balances and transactions have been eliminated in consolidation. Fiscal Year. We report results of operations based on 52 or 53-week periods ending on the Sunday nearest September 30. Fiscal years 2017, 2016 and 2015 contained 52, 53 and 52 weeks, respectively. Use of Estimates. The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America ("U.S. GAAP") requires us to make estimates and assumptions. These estimates and assumptions affect the amounts reported in our consolidated financial statements and accompanying notes. Although such estimates and assumptions are based on management's best knowledge of current events and actions we may take in the future, actual results could differ materially from those estimates. Revenue Recognition and Contract Costs. We recognize revenue for most of our contracts using the percentage-of-completion method, primarily based on contract costs incurred to date compared to total estimated contract costs. We generally utilize the cost-to-cost approach to estimate the progress towards completion in order to determine the amount of revenue and profit to recognize. Revenue and cost estimates for each significant contract are reviewed and reassessed quarterly. Changes in those estimates could result in recognition of cumulative catch-up adjustments to the contract's inception-to-date revenue, costs, and profit in the period in which such changes are made. Changes in revenue and cost estimates could also result in a projected loss that would be recorded immediately in earnings. We recognize revenue for work performed under three major types of contracts: fixed-price, time-and-materials and cost-plus. Fixed-Price. Under fixed-price contracts, our clients pay us an agreed fixed-amount negotiated in advance for a specified scope of work. We generally recognize revenue on fixed-price contracts using the percentage-of-completion method. If the nature or circumstances of the contract prevent us from preparing a reliable estimate at completion, we will delay profit recognition until adequate information about the contract's progress becomes available. Time-and-Materials. Under time-and-materials contracts, we negotiate hourly billing rates and charge our clients based on the actual time that we spend on a project. In addition, clients reimburse us for our actual out-of-pocket costs for materials and other direct incidental expenditures that we incur in connection with our performance under the contract. The majority of our time-and-material contracts are subject to maximum contract values and, accordingly, revenue under these contracts is generally recognized under the percentage-of-completion method. However, time and materials contracts that are service-related contracts are accounted for utilizing the proportional performance method. Revenue on contracts that are not subject to maximum contract values is recognized based on the actual number of hours we spend on the projects plus any actual out-of-pocket costs of materials and other direct incidental expenditures that we incur on the projects. Our time-and-materials contracts also generally include annual billing rate adjustment provisions. Cost-Plus. Under cost-plus contracts, we are reimbursed for allowable or otherwise defined costs incurred plus a negotiated fee. The contracts may also include incentives for various performance criteria, including quality, timeliness, ingenuity, safety and cost-effectiveness. In addition, our costs are generally subject to review by our clients and regulatory audit agencies, and such reviews could result in costs being disputed as non-reimbursable under the terms of the contract. Revenue for cost-plus contracts is recognized at the time services are performed. Revenue is not recognized for non-recoverable costs. Performance incentives are included in our estimates of revenue when their realization is reasonably assured. If estimated total costs on any contract indicate a loss, we recognize the entire estimated loss in the period the loss becomes known. The cumulative effect of revisions to revenue, estimated costs to complete contracts, including penalties, incentive awards, change orders, claims, liquidated damages, anticipated losses, and other revisions are recorded in the period in which the revisions are identified and the loss can be reasonably estimated. Such revisions could occur in any reporting period and the effects may be material depending on the size of the project or the adjustment. Once contract performance is underway, we may experience changes in conditions, client requirements, specifications, designs, materials, and expectations regarding the period of performance. Such changes are "change orders" and may be initiated by us or by our clients. In many cases, agreement with the client as to the terms of change orders is reached prior to work commencing; however, sometimes circumstances require that work progress without obtaining client agreement. Revenue related to change orders is recognized as costs are incurred. Change orders that are unapproved as to both price and scope are evaluated as claims. Claims are amounts in excess of agreed contract prices that we seek to collect from our clients or other third parties for delays, errors in specifications and designs, contract terminations, change orders in dispute or unapproved as to both scope and price, or other causes of unanticipated additional costs. Revenue on claims is recognized only to the extent that contract costs related to the claims have been incurred and when it is probable that the claim will result in a bona fide addition to contract value that can be reliably estimated. No profit is recognized on a claim until final settlement occurs. This can lead to a situation in which costs are recognized in one period and revenue is recognized in a subsequent period when a client agreement is obtained or a claims resolution occurs. Cash and Cash Equivalents. Cash and cash equivalents include all highly liquid investments with maturities of 90 days or less at the date of purchase. Restricted cash of $2.7 million was included in "Prepaid expenses and other current assets" on the consolidated balance sheet at fiscal 2017 year-end. Insurance Matters, Litigation and Contingencies. In the normal course of business, we are subject to certain contractual guarantees and litigation. In addition, we maintain insurance coverage for various aspects of our business and operations. We record in our consolidated balance sheets amounts representing our estimated liability for these legal and insurance obligations. We include any adjustments to these liabilities in our consolidated statements of income. Accounts Receivable – Net. Net accounts receivable is primarily comprised of billed and unbilled accounts receivable, contract retentions and allowances for doubtful accounts. Billed accounts receivable represent amounts billed to clients that have not been collected. Unbilled accounts receivable represent revenue recognized but not yet billed pursuant to contract terms or billed after the period end date. Most of our unbilled receivables at October 1, 2017 are expected to be billed and collected within 12 months. Unbilled accounts receivable also include amounts related to requests for equitable adjustment to contracts that provide for price redetermination. These amounts are recorded only when they can be reliably estimated and realization is probable. Contract retentions represent amounts withheld by clients until certain conditions are met or the project is completed, which may be several months or years. Allowances for doubtful accounts represent the amounts that may become uncollectible or unrealizable in the future. We determine an estimated allowance for uncollectible accounts based on management's consideration of trends in the actual and forecasted credit quality of our clients, including delinquency and payment history; type of client, such as a government agency or a commercial sector client; and general economic and particular industry conditions that may affect a client's ability to pay. Billings in excess of costs on uncompleted contracts represent the amount of cash collected from clients and billings to clients on contracts in advance of work performed and revenue recognized. The majority of these amounts will be earned within 12 months. Property and Equipment. Property and equipment are recorded at cost and are depreciated over their estimated useful lives using the straight-line method. When property and equipment are retired or otherwise disposed of, the cost and accumulated depreciation are removed from our consolidated balance sheets and any resulting gain or loss is reflected in our consolidated statements of income. Expenditures for maintenance and repairs are expensed as incurred. Generally, estimated useful lives range from three to ten years for equipment, furniture and fixtures. Buildings are depreciated over periods not exceeding 40 years. Leasehold improvements are amortized on a straight-line basis over the shorter of their estimated useful lives or the length of the lease. Long-Lived Assets. Our policy regarding long-lived assets is to evaluate the recoverability of our assets when the facts and circumstances suggest that the assets may be impaired. This assessment is performed based on the estimated undiscounted cash flows compared to the carrying value of the assets. If the future cash flows (undiscounted and without interest charges) are less than the carrying value, a write-down would be recorded to reduce the related asset to its estimated fair value. We recognize a liability for contract termination costs associated with an exit activity for costs that will continue to be incurred under a lease for its remaining term without economic benefit to us, initially measured at its fair value at the cease-use date. The fair value is determined based on the remaining lease rentals, adjusted for the effects of any prepaid or deferred items recognized under the lease, and reduced by estimated sublease rentals. Business Combinations. The cost of an acquired company is assigned to the tangible and intangible assets purchased and the liabilities assumed on the basis of their fair values at the date of acquisition. The determination of fair values of assets and liabilities acquired requires us to make estimates and use valuation techniques when a market value is not readily available. Any excess of purchase price over the fair value of net tangible and intangible assets acquired is allocated to goodwill. Goodwill typically represents the value paid for the assembled workforce and enhancement of our service offerings. Transaction costs associated with business combinations are expensed as they are incurred. Goodwill and Intangible Assets. Goodwill represents the excess of the aggregate purchase price over the fair value of the net assets acquired in a business acquisition. Following an acquisition, we perform an analysis to value the acquired company's tangible and identifiable intangible assets and liabilities. With respect to identifiable intangible assets, we consider backlog, non-compete agreements, client relations, trade names, patents and other assets. We amortize our intangible assets based on the period over which the contractual or economic benefits of the intangible assets are expected to be realized. We assess the recoverability of the unamortized balance of our intangible assets when indicators of impairment are present based on expected future profitability and undiscounted expected cash flows and their contribution to our overall operations. Should the review indicate that the carrying value is not fully recoverable, the excess of the carrying value over the fair value of the intangible assets would be recognized as an impairment loss. We test our goodwill for impairment on an annual basis, and more frequently when an event occurs or circumstances indicate that the carrying value of the asset may not be recoverable. We believe the methodology that we use to review impairment of goodwill, which includes a significant amount of judgment and estimates, provides us with a reasonable basis to determine whether impairment has occurred. However, many of the factors employed in determining whether our goodwill is impaired are outside of our control and it is reasonably likely that assumptions and estimates will change in future periods. These changes could result in future impairments. We perform our annual goodwill impairment review at the beginning of our fiscal fourth quarter. Our last annual review was performed at July 3, 2017 (i.e., the first day of our fiscal fourth quarter). In addition, we regularly evaluate whether events and circumstances have occurred that may indicate a potential change in recoverability of goodwill. We perform interim goodwill impairment reviews between our annual reviews if certain events and circumstances have occurred, including a deterioration in general economic conditions, an increased competitive environment, a change in management, key personnel, strategy or customers, negative or declining cash flows, or a decline in actual or planned revenue or earnings compared with actual and projected results of relevant prior periods (See Note 6, "Goodwill and Intangible Assets" for further discussion). We assess goodwill for impairment at the reporting unit level, which is defined as an operating segment or one level below an operating segment, referred to as a component. Our operating segments are the same as our reportable segments and our reporting units for goodwill impairment testing are the components one level below our reportable segments. These components constitute a business for which discrete financial information is available and where segment management regularly reviews the operating results of that component. We aggregate components within an operating segment that have similar economic characteristics. The impairment test for goodwill is a two-step process involving the comparison of the estimated fair value of each reporting unit to the reporting unit's carrying value, including goodwill. We estimate the fair value of reporting units based on a comparison and weighting of the income approach, specifically the discounted cash flow method and the market approach, which estimates the fair value of our reporting units based upon comparable market prices and recent transactions and also validates the reasonableness of the multiples from the income approach. If the fair value of a reporting unit exceeds its carrying amount, the goodwill of the reporting unit is not considered impaired; therefore, the second step of the impairment test is unnecessary. If the carrying amount of a reporting unit exceeds its fair value, we perform the second step of the goodwill impairment test to measure the amount of impairment loss to be recorded. If our goodwill is impaired, we are required to record a non-cash charge that could have a material adverse effect on our consolidated financial statements. Contingent Consideration. Most of our acquisition agreements include contingent earn-out arrangements, which are generally based on the achievement of future operating income thresholds. The contingent earn-out arrangements are based upon our valuations of the acquired companies and reduce the risk of overpaying for acquisitions if the projected financial results are not achieved. The fair values of these earn-out arrangements are included as part of the purchase price of the acquired companies on their respective acquisition dates. For each transaction, we estimate the fair value of contingent earn-out payments as part of the initial purchase price and record the estimated fair value of contingent consideration as a liability in "Current contingent earn-out liabilities" and "Long-term contingent earn-out liabilities" on the consolidated balance sheets. We consider several factors when determining that contingent earn-out liabilities are part of the purchase price, including the following: (1) the valuation of our acquisitions is not supported solely by the initial consideration paid, and the contingent earn-out formula is a critical and material component of the valuation approach to determining the purchase price; and (2) the former owners of acquired companies that remain as key employees receive compensation other than contingent earn-out payments at a reasonable level compared with the compensation of our other key employees. The contingent earn-out payments are not affected by employment termination. We measure our contingent earn-out liabilities at fair value on a recurring basis using significant unobservable inputs classified within Level 3 of the fair value hierarchy. We use a probability weighted discounted income approach as a valuation technique to convert future estimated cash flows to a single present value amount. The significant unobservable inputs used in the fair value measurements are operating income projections over the earn-out period (generally two or three years), and the probability outcome percentages we assign to each scenario. Significant increases or decreases to either of these inputs in isolation would result in a significantly higher or lower liability with a higher liability capped by the contractual maximum of the contingent earn-out obligation. Ultimately, the liability will be equivalent to the amount paid, and the difference between the fair value estimate and amount paid will be recorded in earnings. The amount paid that is less than or equal to the liability on the acquisition date is reflected as cash used in financing activities in our consolidated statements of cash flows. Any amount paid in excess of the liability on the acquisition date is reflected as cash used in operating activities. We review and re-assess the estimated fair value of contingent consideration on a quarterly basis, and the updated fair value could differ materially from the initial estimates. Changes in the estimated fair value of our contingent earn-out liabilities related to the time component of the present value calculation are reported in interest expense. Adjustments to the estimated fair value related to changes in all other unobservable inputs are reported in operating income. Fair Value of Financial Instruments. We determine the fair values of our financial instruments, including short-term investments, debt instruments and derivative instruments based on inputs or assumptions that market participants would use in pricing an asset or a liability. We categorize our instruments using a valuation hierarchy for disclosure of the inputs used to measure fair value. This hierarchy prioritizes the inputs into three broad levels as follows: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; Level 2 inputs are quoted prices for similar assets and liabilities in active markets or inputs that are observable for the asset or liability, either directly or indirectly through market corroboration, for substantially the full term of the financial instrument; and Level 3 inputs are unobservable inputs based on our own assumptions used to measure assets and liabilities at fair value. The classification of a financial asset or liability within the hierarchy is determined based on the lowest level input that is significant to the fair value measurement. The carrying amounts of cash and cash equivalents, accounts receivable and accounts payable approximate fair values based on their short-term nature. The carrying amounts of our revolving credit facility approximates fair value because the interest rates are based upon variable reference rates (see Note 9, "Long-Term Debt" and Note 14, "Derivative Financial Instruments" for additional disclosure). Certain other assets and liabilities, such as contingent earn-out liabilities, assets held for sale and amounts related to cash-flow hedges, are required to be carried in our consolidated financial statements at fair value. Our fair value measurement methods may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Although we believe our valuation methods are appropriate and consistent with those used by other market participants, the use of different methodologies or assumptions to determine fair value could result in a different fair value measurement at the reporting date. Derivative Financial Instruments. We account for our derivative instruments as either assets or liabilities and carry them at fair value. For derivative instruments that hedge the exposure to variability in expected future cash flows that are designated as cash flow hedges, the effective portion of the gain or loss on the derivative instrument is reported as a component of accumulated other comprehensive income (loss) in stockholders' equity and reclassified into income in the same period or periods during which the hedged transaction affects earnings. The ineffective portion of the gain or loss on the derivative instrument, if any, is recognized in current income. To receive hedge accounting treatment, cash flow hedges must be highly effective in offsetting changes to expected future cash flows on hedged transactions. The net gain or loss on the effective portion of a derivative instrument that is designated as an economic hedge of the foreign currency translation exposure generated by the re-measurement of certain assets and liabilities denominated in a non-functional currency in a foreign operation is reported in the same manner as a foreign currency translation adjustment. Accordingly, any gains or losses related to these derivative instruments are recognized in current income. Derivatives that do not qualify as hedges are adjusted to fair value through current income. Deferred Compensation. We maintain a non-qualified defined contribution supplemental retirement plan for certain key employees and non-employee directors that is accounted for in accordance with applicable authoritative guidance on accounting for deferred compensation arrangements where amounts earned are held in a rabbi trust and invested. Employee deferrals and our match are deposited into a rabbi trust, and the funds are generally invested in individual variable life insurance contracts that we own and are specifically designed to informally fund savings plans of this nature. Our consolidated balance sheets reflect our investment in variable life insurance contracts in "Other long-term assets." Our obligation to participating employees is reflected in "Other long-term liabilities." All income and expenses related to the rabbi trust are reflected in our consolidated statements of income. Income Taxes. We file a consolidated U.S. federal income tax return and a combined California franchise tax return. In addition, we file other returns that are required in the states, foreign jurisdictions and other jurisdictions in which we do business. We account for certain income and expense items differently for financial reporting and income tax purposes. Deferred tax assets and liabilities are computed for the difference between the financial statement and tax bases of assets and liabilities that will result in taxable or deductible amounts in the future based on enacted tax laws and rates applicable to the periods in which the differences are expected to reverse. In determining the need for a valuation allowance, management reviews both positive and negative evidence, including current and historical results of operations, future income projections and potential tax planning strategies. Based on our assessment, we have concluded that a portion of the deferred tax assets at October 1, 2017 will not be realized. According to the authoritative guidance on accounting for uncertainty in income taxes, we may recognize the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities based on the technical merits of the position. The tax benefits recognized in the financial statements from such a position should be measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. This guidance also addresses de-recognition, classification, interest and penalties on income taxes, accounting in interim periods and disclosure requirements for uncertain tax positions. Concentration of Credit Risk. Financial instruments that subject us to credit risk consist primarily of cash and cash equivalents and net accounts receivable. In the event that we have surplus cash, we place our temporary cash investments with lower risk financial institutions and, by policy, limit the amount of investment exposure to any one financial institution. Approximately 23% of accounts receivable were due from various agencies of the U.S. federal government at fiscal 2017 year-end. The remaining accounts receivable are generally diversified due to the large number of organizations comprising our client base and their geographic dispersion. We perform ongoing credit evaluations of our clients and maintain an allowance for potential credit losses. Approximately 45%, 28% and 27% of our fiscal 2017 revenue was generated from our U.S government, U.S. commercial and international clients, respectively (see Note 18, "Reportable Segments" for more information). Foreign Currency Translation. We determine the functional currency of our foreign operating units based upon the primary currency in which they operate. These operating units maintain their accounting records in their local currency, primarily Canadian and Australian dollars. Where the functional currency is not the U.S. dollar, translation of assets and liabilities to U.S. dollars is based on exchange rates at the balance sheet date. Translation of revenue and expenses to U.S. dollars is based on the average rate during the period. Translation gains or losses are reported as a component of other comprehensive income (loss). Gains or losses from foreign currency transactions are included in results of operations, with the exception of intercompany foreign transactions that are considered long-term investments, which are recorded in "Accumulated other comprehensive income (loss)" on the consolidated balance sheets. Recently Adopted and Pending Accounting Guidance. In March 2016, the Financial Accounting Standards Board (“FASB”) issued updated guidance which requires excess tax benefits and deficiencies on share-based payments to be recorded as income tax expense or benefit in the income statement rather than being recorded in additional paid-in capital. This guidance is effective for annual and interim periods beginning after December 15, 2016, with early adoption permitted. During the first quarter of fiscal 2017, we adopted this guidance and, as a result, we recognized income tax benefits of $4.9 million in our consolidated statement of income for fiscal 2017. We also reported $4.9 million as part of our cash flows from operating activities on our consolidated statement of cash flows for fiscal 2017. In May 2014, the FASB issued an accounting standard that will supersede existing revenue recognition guidance under current U.S. GAAP. The new standard is a comprehensive new revenue recognition model that requires a company to recognize revenue to depict the transfer of goods or services to a customer at an amount that reflects the consideration it expects to receive in exchange for those goods and services. The standard may be applied retrospectively to each prior period presented or retrospectively with the cumulative effect recognized as of the date of initial application. We continue to evaluate the impact of the new guidance on our consolidated financial statements. We expect to adopt the new standard on October 1, 2018 (the first day of fiscal 2019), using the modified retrospective method that may result in a cumulative effect adjustment as of the date of adoption. In January 2015, the FASB issued an amendment to the accounting guidance related to the income statement presentation of extraordinary and unusual items. The amendment eliminates from U.S. GAAP the concept of extraordinary items. The guidance was effective for us in the first quarter of fiscal 2017, and the adoption of this guidance had no impact on our consolidated financial statements. In January 2016, the FASB issued guidance that generally requires companies to measure investments in other entities, except those accounted for under the equity method, at fair value and recognize any changes in fair value in net income. The guidance is effective for us in the first quarter of fiscal 2018. We do not expect the adoption of this guidance to have a significant impact on our consolidated financial statements. In February 2016, the FASB issued guidance that primarily requires lessees to recognize most leases on their balance sheets but record expenses on their income statements in a manner similar to current accounting. For lessors, the guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. The guidance is effective for us in the first quarter of fiscal 2020, with early adoption permitted. We are currently evaluating the impact that this guidance will have on our consolidated financial statements. In June 2016, the FASB issued updated guidance which requires entities to estimate all expected credit losses for certain types of financial instruments, including trade receivables, held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. The updated guidance also expands the disclosure requirements to enable users of financial statements to understand the entity’s assumptions, models and methods for estimating expected credit losses. This guidance is effective for us in the first quarter of fiscal 2021, with early adoption permitted. We are currently evaluating the impact that this guidance will have on our consolidated financial statements. In August 2016, the FASB issued guidance to address eight specific cash flow issues to reduce the existing diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. This guidance is effective for us in the first quarter of fiscal 2019, with early adoption permitted. We are currently evaluating the impact that this guidance will have on our consolidated financial statements. In October 2016, the FASB issued updated guidance which requires entities to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. This guidance is effective for us in the first quarter of fiscal 2019, with early adoption permitted. We are currently evaluating the impact that this guidance will have on our consolidated financial statements. In November 2016, the FASB issued updated guidance which provides amendments to address the classification and presentation of changes in restricted cash and in the statement of cash flows. This guidance is effective for us in the first quarter of fiscal 2018. We do not expect that this guidance will have a material impact on our consolidated financial statements. In January 2017, the FASB issued new guidance that changes the definition of a business to assist entities with evaluating when a set of transferred assets and activities is a business. The guidance requires an entity to evaluate if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or a group of similar identifiable assets; if so, the set of transferred assets and activities is not a business. This guidance is effective for us in the first quarter of fiscal year 2019, and interim periods within those years, with early adoption permitted. We adopted this guidance in the first quarter of fiscal 2017, and the adoption of this guidance had no impact on our consolidated financial statements. In January 2017, the FASB issued updated guidance to simplify the test for goodwill impairment. This guidance eliminates step two from the goodwill impairment test. Under the updated guidance, an entity should recognize an impairment charge for the amount by which the carrying amount of a reporting unit exceeds its fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to the reporting unit. This guidance is effective for us in the first quarter of fiscal 2021, on a prospective basis, and earlier adoption is permitted for goodwill impairment tests performed on testing dates after January 1, 2017. We plan to adopt this guidance in the first quarter of fiscal 2018 and we do not expect the adoption of this guidance to have a material impact on our consolidated financial statements. In May 2017, the FASB issued updated guidance to clarify when changes to the terms or conditions of a share-based payment award must be accounted for as modifications. Under the updated guidance, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award changes as a result of the change in terms or conditions. This guidance is effective for us in the first quarter of fiscal year 2019, on a prospective basis, with early adoption permitted. We are currently evaluating the impact that this guidance will have on our consolidated financial statements. In August 2017, the FASB issued accounting guidance on hedging activities. The amendment better aligns an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. This guidance is effective for us in the first quarter of fiscal 2020, and interim periods within those years, with early adoption permitted. We are currently evaluating the impact of this guidance will have on our consolidated financial statements.

Basis of Presentation and Preparation

Principles of Consolidation and Presentation. The consolidated financial statements include our accounts and those of joint ventures of which we are the primary beneficiary. All significant intercompany balances and transactions have been eliminated in consolidation.

Fiscal Year. We report results of operations based on 52 or 53-week periods ending on the Sunday nearest September 30. Fiscal years 2017, 2016 and 2015 contained 52, 53 and 52 weeks, respectively.

Use of Estimates. The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America ("U.S. GAAP") requires us to make estimates and assumptions. These estimates and assumptions affect the amounts reported in our consolidated financial statements and accompanying notes. Although such estimates and assumptions are based on management's best knowledge of current events and actions we may take in the future, actual results could differ materially from those estimates.

Revenue Recognition and Contract Costs. We recognize revenue for most of our contracts using the percentage-of-completion method, primarily based on contract costs incurred to date compared to total estimated contract costs. We generally utilize the cost-to-cost approach to estimate the progress towards completion in order to determine the amount of revenue and profit to recognize. Revenue and cost estimates for each significant contract are reviewed and reassessed quarterly. Changes in those estimates could result in recognition of cumulative catch-up adjustments to the contract's inception-to-date revenue, costs, and profit in the period in which such changes are made. Changes in revenue and cost estimates could also result in a projected loss that would be recorded immediately in earnings.

We recognize revenue for work performed under three major types of contracts: fixed-price, time-and-materials and cost-plus.

Fixed-Price. Under fixed-price contracts, our clients pay us an agreed fixed-amount negotiated in advance for a specified scope of work. We generally recognize revenue on fixed-price contracts using the percentage-of-completion method. If the nature or circumstances of the contract prevent us from preparing a reliable estimate at completion, we will delay profit recognition until adequate information about the contract's progress becomes available.

Time-and-Materials. Under time-and-materials contracts, we negotiate hourly billing rates and charge our clients based on the actual time that we spend on a project. In addition, clients reimburse us for our actual out-of-pocket costs for materials and other direct incidental expenditures that we incur in connection with our performance under the contract. The majority of our time-and-material contracts are subject to maximum contract values and, accordingly, revenue under these contracts is generally recognized under the percentage-of-completion method. However, time and materials contracts that are service-related contracts are accounted for utilizing the proportional performance method. Revenue on contracts that are not subject to maximum contract values is recognized based on the actual number of hours we spend on the projects plus any actual out-of-pocket costs of materials and other direct incidental expenditures that we incur on the projects. Our time-and-materials contracts also generally include annual billing rate adjustment provisions.

Cost-Plus. Under cost-plus contracts, we are reimbursed for allowable or otherwise defined costs incurred plus a negotiated fee. The contracts may also include incentives for various performance criteria, including quality, timeliness, ingenuity, safety and cost-effectiveness. In addition, our costs are generally subject to review by our clients and regulatory audit agencies, and such reviews could result in costs being disputed as non-reimbursable under the terms of the contract. Revenue for cost-plus contracts is recognized at the time services are performed. Revenue is not recognized for non-recoverable costs. Performance incentives are included in our estimates of revenue when their realization is reasonably assured.

If estimated total costs on any contract indicate a loss, we recognize the entire estimated loss in the period the loss becomes known. The cumulative effect of revisions to revenue, estimated costs to complete contracts, including penalties, incentive awards, change orders, claims, liquidated damages, anticipated losses, and other revisions are recorded in the period in which the revisions are identified and the loss can be reasonably estimated. Such revisions could occur in any reporting period and the effects may be material depending on the size of the project or the adjustment.

Once contract performance is underway, we may experience changes in conditions, client requirements, specifications, designs, materials, and expectations regarding the period of performance. Such changes are "change orders" and may be initiated by us or by our clients. In many cases, agreement with the client as to the terms of change orders is reached prior to work commencing; however, sometimes circumstances require that work progress without obtaining client agreement. Revenue related to change orders is recognized as costs are incurred. Change orders that are unapproved as to both price and scope are evaluated as claims.

Claims are amounts in excess of agreed contract prices that we seek to collect from our clients or other third parties for delays, errors in specifications and designs, contract terminations, change orders in dispute or unapproved as to both scope and price, or other causes of unanticipated additional costs. Revenue on claims is recognized only to the extent that contract costs related to the claims have been incurred and when it is probable that the claim will result in a bona fide addition to contract value that can be reliably estimated. No profit is recognized on a claim until final settlement occurs. This can lead to a situation in which costs are recognized in one period and revenue is recognized in a subsequent period when a client agreement is obtained or a claims resolution occurs.

Cash and Cash Equivalents. Cash and cash equivalents include all highly liquid investments with maturities of 90 days or less at the date of purchase. Restricted cash of $2.7 million was included in "Prepaid expenses and other current assets" on the consolidated balance sheet at fiscal 2017 year-end.

Insurance Matters, Litigation and Contingencies. In the normal course of business, we are subject to certain contractual guarantees and litigation. In addition, we maintain insurance coverage for various aspects of our business and operations. We record in our consolidated balance sheets amounts representing our estimated liability for these legal and insurance obligations. We include any adjustments to these liabilities in our consolidated statements of income.

Accounts Receivable – Net. Net accounts receivable is primarily comprised of billed and unbilled accounts receivable, contract retentions and allowances for doubtful accounts. Billed accounts receivable represent amounts billed to clients that have not been collected. Unbilled accounts receivable represent revenue recognized but not yet billed pursuant to contract terms or billed after the period end date. Most of our unbilled receivables at October 1, 2017 are expected to be billed and collected within 12 months. Unbilled accounts receivable also include amounts related to requests for equitable adjustment to contracts that provide for price redetermination. These amounts are recorded only when they can be reliably estimated and realization is probable. Contract retentions represent amounts withheld by clients until certain conditions are met or the project is completed, which may be several months or years. Allowances for doubtful accounts represent the amounts that may become uncollectible or unrealizable in the future. We determine an estimated allowance for uncollectible accounts based on management's consideration of trends in the actual and forecasted credit quality of our clients, including delinquency and payment history; type of client, such as a government agency or a commercial sector client; and general economic and particular industry conditions that may affect a client's ability to pay. Billings in excess of costs on uncompleted contracts represent the amount of cash collected from clients and billings to clients on contracts in advance of work performed and revenue recognized. The majority of these amounts will be earned within 12 months.

Property and Equipment. Property and equipment are recorded at cost and are depreciated over their estimated useful lives using the straight-line method. When property and equipment are retired or otherwise disposed of, the cost and accumulated depreciation are removed from our consolidated balance sheets and any resulting gain or loss is reflected in our consolidated statements of income. Expenditures for maintenance and repairs are expensed as incurred. Generally, estimated useful lives range from three to ten years for equipment, furniture and fixtures. Buildings are depreciated over periods not exceeding 40 years. Leasehold improvements are amortized on a straight-line basis over the shorter of their estimated useful lives or the length of the lease.

Long-Lived Assets. Our policy regarding long-lived assets is to evaluate the recoverability of our assets when the facts and circumstances suggest that the assets may be impaired. This assessment is performed based on the estimated undiscounted cash flows compared to the carrying value of the assets. If the future cash flows (undiscounted and without interest charges) are less than the carrying value, a write-down would be recorded to reduce the related asset to its estimated fair value.

We recognize a liability for contract termination costs associated with an exit activity for costs that will continue to be incurred under a lease for its remaining term without economic benefit to us, initially measured at its fair value at the cease-use date. The fair value is determined based on the remaining lease rentals, adjusted for the effects of any prepaid or deferred items recognized under the lease, and reduced by estimated sublease rentals.

Business Combinations. The cost of an acquired company is assigned to the tangible and intangible assets purchased and the liabilities assumed on the basis of their fair values at the date of acquisition. The determination of fair values of assets and liabilities acquired requires us to make estimates and use valuation techniques when a market value is not readily available. Any excess of purchase price over the fair value of net tangible and intangible assets acquired is allocated to goodwill. Goodwill typically represents the value paid for the assembled workforce and enhancement of our service offerings. Transaction costs associated with business combinations are expensed as they are incurred.

Goodwill and Intangible Assets. Goodwill represents the excess of the aggregate purchase price over the fair value of the net assets acquired in a business acquisition. Following an acquisition, we perform an analysis to value the acquired company's tangible and identifiable intangible assets and liabilities. With respect to identifiable intangible assets, we consider backlog, non-compete agreements, client relations, trade names, patents and other assets. We amortize our intangible assets based on the period over which the contractual or economic benefits of the intangible assets are expected to be realized. We assess the recoverability of the unamortized balance of our intangible assets when indicators of impairment are present based on expected future profitability and undiscounted expected cash flows and their contribution to our overall operations. Should the review indicate that the carrying value is not fully recoverable, the excess of the carrying value over the fair value of the intangible assets would be recognized as an impairment loss.

We test our goodwill for impairment on an annual basis, and more frequently when an event occurs or circumstances indicate that the carrying value of the asset may not be recoverable. We believe the methodology that we use to review impairment of goodwill, which includes a significant amount of judgment and estimates, provides us with a reasonable basis to determine whether impairment has occurred. However, many of the factors employed in determining whether our goodwill is impaired are outside of our control and it is reasonably likely that assumptions and estimates will change in future periods. These changes could result in future impairments.

We perform our annual goodwill impairment review at the beginning of our fiscal fourth quarter. Our last annual review was performed at July 3, 2017 (i.e., the first day of our fiscal fourth quarter). In addition, we regularly evaluate whether events and circumstances have occurred that may indicate a potential change in recoverability of goodwill. We perform interim goodwill impairment reviews between our annual reviews if certain events and circumstances have occurred, including a deterioration in general economic conditions, an increased competitive environment, a change in management, key personnel, strategy or customers, negative or declining cash flows, or a decline in actual or planned revenue or earnings compared with actual and projected results of relevant prior periods (See Note 6, "Goodwill and Intangible Assets" for further discussion). We assess goodwill for impairment at the reporting unit level, which is defined as an operating segment or one level below an operating segment, referred to as a component. Our operating segments are the same as our reportable segments and our reporting units for goodwill impairment testing are the components one level below our reportable segments. These components constitute a business for which discrete financial information is available and where segment management regularly reviews the operating results of that component. We aggregate components within an operating segment that have similar economic characteristics.

The impairment test for goodwill is a two-step process involving the comparison of the estimated fair value of each reporting unit to the reporting unit's carrying value, including goodwill. We estimate the fair value of reporting units based on a comparison and weighting of the income approach, specifically the discounted cash flow method and the market approach, which estimates the fair value of our reporting units based upon comparable market prices and recent transactions and also validates the reasonableness of the multiples from the income approach. If the fair value of a reporting unit exceeds its carrying amount, the goodwill of the reporting unit is not considered impaired; therefore, the second step of the impairment test is unnecessary. If the carrying amount of a reporting unit exceeds its fair value, we perform the second step of the goodwill impairment test to measure the amount of impairment loss to be recorded. If our goodwill is impaired, we are required to record a non-cash charge that could have a material adverse effect on our consolidated financial statements.

Contingent Consideration. Most of our acquisition agreements include contingent earn-out arrangements, which are generally based on the achievement of future operating income thresholds. The contingent earn-out arrangements are based upon our valuations of the acquired companies and reduce the risk of overpaying for acquisitions if the projected financial results are not achieved.

The fair values of these earn-out arrangements are included as part of the purchase price of the acquired companies on their respective acquisition dates. For each transaction, we estimate the fair value of contingent earn-out payments as part of the initial purchase price and record the estimated fair value of contingent consideration as a liability in "Current contingent earn-out liabilities" and "Long-term contingent earn-out liabilities" on the consolidated balance sheets. We consider several factors when determining that contingent earn-out liabilities are part of the purchase price, including the following: (1) the valuation of our acquisitions is not supported solely by the initial consideration paid, and the contingent earn-out formula is a critical and material component of the valuation approach to determining the purchase price; and (2) the former owners of acquired companies that remain as key employees receive compensation other than contingent earn-out payments at a reasonable level compared with the compensation of our other key employees. The contingent earn-out payments are not affected by employment termination.

We measure our contingent earn-out liabilities at fair value on a recurring basis using significant unobservable inputs classified within Level 3 of the fair value hierarchy. We use a probability weighted discounted income approach as a valuation technique to convert future estimated cash flows to a single present value amount. The significant unobservable inputs used in the fair value measurements are operating income projections over the earn-out period (generally two or three years), and the probability outcome percentages we assign to each scenario. Significant increases or decreases to either of these inputs in isolation would result in a significantly higher or lower liability with a higher liability capped by the contractual maximum of the contingent earn-out obligation. Ultimately, the liability will be equivalent to the amount paid, and the difference between the fair value estimate and amount paid will be recorded in earnings. The amount paid that is less than or equal to the liability on the acquisition date is reflected as cash used in financing activities in our consolidated statements of cash flows. Any amount paid in excess of the liability on the acquisition date is reflected as cash used in operating activities.

We review and re-assess the estimated fair value of contingent consideration on a quarterly basis, and the updated fair value could differ materially from the initial estimates. Changes in the estimated fair value of our contingent earn-out liabilities related to the time component of the present value calculation are reported in interest expense. Adjustments to the estimated fair value related to changes in all other unobservable inputs are reported in operating income.

Fair Value of Financial Instruments. We determine the fair values of our financial instruments, including short-term investments, debt instruments and derivative instruments based on inputs or assumptions that market participants would use in pricing an asset or a liability. We categorize our instruments using a valuation hierarchy for disclosure of the inputs used to measure fair value. This hierarchy prioritizes the inputs into three broad levels as follows: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; Level 2 inputs are quoted prices for similar assets and liabilities in active markets or inputs that are observable for the asset or liability, either directly or indirectly through market corroboration, for substantially the full term of the financial instrument; and Level 3 inputs are unobservable inputs based on our own assumptions used to measure assets and liabilities at fair value. The classification of a financial asset or liability within the hierarchy is determined based on the lowest level input that is significant to the fair value measurement.

The carrying amounts of cash and cash equivalents, accounts receivable and accounts payable approximate fair values based on their short-term nature. The carrying amounts of our revolving credit facility approximates fair value because the interest rates are based upon variable reference rates (see Note 9, "Long-Term Debt" and Note 14, "Derivative Financial Instruments" for additional disclosure). Certain other assets and liabilities, such as contingent earn-out liabilities, assets held for sale and amounts related to cash-flow hedges, are required to be carried in our consolidated financial statements at fair value.

Our fair value measurement methods may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Although we believe our valuation methods are appropriate and consistent with those used by other market participants, the use of different methodologies or assumptions to determine fair value could result in a different fair value measurement at the reporting date.

Derivative Financial Instruments. We account for our derivative instruments as either assets or liabilities and carry them at fair value. For derivative instruments that hedge the exposure to variability in expected future cash flows that are designated as cash flow hedges, the effective portion of the gain or loss on the derivative instrument is reported as a component of accumulated other comprehensive income (loss) in stockholders' equity and reclassified into income in the same period or periods during which the hedged transaction affects earnings. The ineffective portion of the gain or loss on the derivative instrument, if any, is recognized in current income. To receive hedge accounting treatment, cash flow hedges must be highly effective in offsetting changes to expected future cash flows on hedged transactions.

The net gain or loss on the effective portion of a derivative instrument that is designated as an economic hedge of the foreign currency translation exposure generated by the re-measurement of certain assets and liabilities denominated in a non-functional currency in a foreign operation is reported in the same manner as a foreign currency translation adjustment. Accordingly, any gains or losses related to these derivative instruments are recognized in current income. Derivatives that do not qualify as hedges are adjusted to fair value through current income.

Deferred Compensation. We maintain a non-qualified defined contribution supplemental retirement plan for certain key employees and non-employee directors that is accounted for in accordance with applicable authoritative guidance on accounting for deferred compensation arrangements where amounts earned are held in a rabbi trust and invested. Employee deferrals and our match are deposited into a rabbi trust, and the funds are generally invested in individual variable life insurance contracts that we own and are specifically designed to informally fund savings plans of this nature. Our consolidated balance sheets reflect our investment in variable life insurance contracts in "Other long-term assets." Our obligation to participating employees is reflected in "Other long-term liabilities." All income and expenses related to the rabbi trust are reflected in our consolidated statements of income.

Income Taxes. We file a consolidated U.S. federal income tax return and a combined California franchise tax return. In addition, we file other returns that are required in the states, foreign jurisdictions and other jurisdictions in which we do business. We account for certain income and expense items differently for financial reporting and income tax purposes. Deferred tax assets and liabilities are computed for the difference between the financial statement and tax bases of assets and liabilities that will result in taxable or deductible amounts in the future based on enacted tax laws and rates applicable to the periods in which the differences are expected to reverse. In determining the need for a valuation allowance, management reviews both positive and negative evidence, including current and historical results of operations, future income projections and potential tax planning strategies. Based on our assessment, we have concluded that a portion of the deferred tax assets at October 1, 2017 will not be realized.

According to the authoritative guidance on accounting for uncertainty in income taxes, we may recognize the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities based on the technical merits of the position. The tax benefits recognized in the financial statements from such a position should be measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. This guidance also addresses de-recognition, classification, interest and penalties on income taxes, accounting in interim periods and disclosure requirements for uncertain tax positions.

Concentration of Credit Risk. Financial instruments that subject us to credit risk consist primarily of cash and cash equivalents and net accounts receivable. In the event that we have surplus cash, we place our temporary cash investments with lower risk financial institutions and, by policy, limit the amount of investment exposure to any one financial institution. Approximately 23% of accounts receivable were due from various agencies of the U.S. federal government at fiscal 2017 year-end. The remaining accounts receivable are generally diversified due to the large number of organizations comprising our client base and their geographic dispersion. We perform ongoing credit evaluations of our clients and maintain an allowance for potential credit losses. Approximately 45%, 28% and 27% of our fiscal 2017 revenue was generated from our U.S government, U.S. commercial and international clients, respectively (see Note 18, "Reportable Segments" for more information).

Foreign Currency Translation. We determine the functional currency of our foreign operating units based upon the primary currency in which they operate. These operating units maintain their accounting records in their local currency, primarily Canadian and Australian dollars. Where the functional currency is not the U.S. dollar, translation of assets and liabilities to U.S. dollars is based on exchange rates at the balance sheet date. Translation of revenue and expenses to U.S. dollars is based on the average rate during the period. Translation gains or losses are reported as a component of other comprehensive income (loss). Gains or losses from foreign currency transactions are included in results of operations, with the exception of intercompany foreign transactions that are considered long-term investments, which are recorded in "Accumulated other comprehensive income (loss)" on the consolidated balance sheets.

Recently Adopted and Pending Accounting Guidance. In March 2016, the Financial Accounting Standards Board (“FASB”) issued updated guidance which requires excess tax benefits and deficiencies on share-based payments to be recorded as income tax expense or benefit in the income statement rather than being recorded in additional paid-in capital. This guidance is effective for annual and interim periods beginning after December 15, 2016, with early adoption permitted. During the first quarter of fiscal 2017, we adopted this guidance and, as a result, we recognized income tax benefits of $4.9 million in our consolidated statement of income for fiscal 2017. We also reported $4.9 million as part of our cash flows from operating activities on our consolidated statement of cash flows for fiscal 2017.

In May 2014, the FASB issued an accounting standard that will supersede existing revenue recognition guidance under current U.S. GAAP. The new standard is a comprehensive new revenue recognition model that requires a company to recognize revenue to depict the transfer of goods or services to a customer at an amount that reflects the consideration it expects to receive in exchange for those goods and services. The standard may be applied retrospectively to each prior period presented or retrospectively with the cumulative effect recognized as of the date of initial application. We continue to evaluate the impact of the new guidance on our consolidated financial statements. We expect to adopt the new standard on October 1, 2018 (the first day of fiscal 2019), using the modified retrospective method that may result in a cumulative effect adjustment as of the date of adoption.

In January 2015, the FASB issued an amendment to the accounting guidance related to the income statement presentation of extraordinary and unusual items. The amendment eliminates from U.S. GAAP the concept of extraordinary items. The guidance was effective for us in the first quarter of fiscal 2017, and the adoption of this guidance had no impact on our consolidated financial statements.

In January 2016, the FASB issued guidance that generally requires companies to measure investments in other entities, except those accounted for under the equity method, at fair value and recognize any changes in fair value in net income. The guidance is effective for us in the first quarter of fiscal 2018. We do not expect the adoption of this guidance to have a significant impact on our consolidated financial statements.

In February 2016, the FASB issued guidance that primarily requires lessees to recognize most leases on their balance sheets but record expenses on their income statements in a manner similar to current accounting. For lessors, the guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. The guidance is effective for us in the first quarter of fiscal 2020, with early adoption permitted. We are currently evaluating the impact that this guidance will have on our consolidated financial statements.

In June 2016, the FASB issued updated guidance which requires entities to estimate all expected credit losses for certain types of financial instruments, including trade receivables, held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. The updated guidance also expands the disclosure requirements to enable users of financial statements to understand the entity’s assumptions, models and methods for estimating expected credit losses. This guidance is effective for us in the first quarter of fiscal 2021, with early adoption permitted. We are currently evaluating the impact that this guidance will have on our consolidated financial statements.

In August 2016, the FASB issued guidance to address eight specific cash flow issues to reduce the existing diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. This guidance is effective for us in the first quarter of fiscal 2019, with early adoption permitted. We are currently evaluating the impact that this guidance will have on our consolidated financial statements.

In October 2016, the FASB issued updated guidance which requires entities to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. This guidance is effective for us in the first quarter of fiscal 2019, with early adoption permitted. We are currently evaluating the impact that this guidance will have on our consolidated financial statements.

In November 2016, the FASB issued updated guidance which provides amendments to address the classification and presentation of changes in restricted cash and in the statement of cash flows. This guidance is effective for us in the first quarter of fiscal 2018. We do not expect that this guidance will have a material impact on our consolidated financial statements.

In January 2017, the FASB issued new guidance that changes the definition of a business to assist entities with evaluating when a set of transferred assets and activities is a business. The guidance requires an entity to evaluate if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or a group of similar identifiable assets; if so, the set of transferred assets and activities is not a business. This guidance is effective for us in the first quarter of fiscal year 2019, and interim periods within those years, with early adoption permitted. We adopted this guidance in the first quarter of fiscal 2017, and the adoption of this guidance had no impact on our consolidated financial statements.

In January 2017, the FASB issued updated guidance to simplify the test for goodwill impairment. This guidance eliminates step two from the goodwill impairment test. Under the updated guidance, an entity should recognize an impairment charge for the amount by which the carrying amount of a reporting unit exceeds its fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to the reporting unit. This guidance is effective for us in the first quarter of fiscal 2021, on a prospective basis, and earlier adoption is permitted for goodwill impairment tests performed on testing dates after January 1, 2017. We plan to adopt this guidance in the first quarter of fiscal 2018 and we do not expect the adoption of this guidance to have a material impact on our consolidated financial statements.

In May 2017, the FASB issued updated guidance to clarify when changes to the terms or conditions of a share-based payment award must be accounted for as modifications. Under the updated guidance, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award changes as a result of the change in terms or conditions. This guidance is effective for us in the first quarter of fiscal year 2019, on a prospective basis, with early adoption permitted. We are currently evaluating the impact that this guidance will have on our consolidated financial statements.

In August 2017, the FASB issued accounting guidance on hedging activities. The amendment better aligns an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. This guidance is effective for us in the first quarter of fiscal 2020, and interim periods within those years, with early adoption permitted. We are currently evaluating the impact of this guidance will have on our consolidated financial statements.