Tetra Tech (TTEK) 10-K 20 Nov 17 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Oct. 01, 2017	Nov. 01, 2017	Apr. 02, 2017
Document and Entity Information
Entity Registrant Name	TETRA TECH INC
Entity Central Index Key	831,641
Current Fiscal Year End Date	--10-01
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Oct. 1, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		55,722,592
Entity Public Float			$ 2.3

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Oct. 01, 2017	Oct. 02, 2016
Current assets:
Cash and cash equivalents	$ 189,975	$ 160,459
Accounts receivable – net	788,767	714,336
Prepaid expenses and other current assets	49,969	46,262
Income taxes receivable	13,312	14,371
Total current assets	1,042,023	935,428
Property and equipment – net	56,835	67,827
Investments in and advances to unconsolidated joint ventures	2,700	2,064
Goodwill	740,886	717,988
Intangible assets – net	26,688	48,962
Deferred income taxes	1,763	630
Other long-term assets	31,850	27,880
Total assets	1,902,745	1,800,779
Current liabilities:
Accounts payable	177,638	158,773
Accrued compensation	143,408	129,184
Billings in excess of costs on uncompleted contracts	117,499	88,223
Current portion of long-term debt	15,588	15,510
Current contingent earn-out liabilities	2,024	4,296
Other current liabilities	81,511	85,100
Total current liabilities	537,668	481,086
Deferred income taxes	43,781	60,348
Long-term debt	341,283	331,501
Long-term contingent earn-out liabilities	414	4,461
Other long-term liabilities	50,975	53,980
Commitments and contingencies (Note 17)
Equity:
Preferred stock – Authorized, 2,000 shares of $0.01 par value; no shares issued and outstanding at October 1, 2017 and October 2, 2016	0	0
Common stock – Authorized, 150,000 shares of $0.01 par value; issued and outstanding, 55,873 and 57,042 shares at October 1, 2017 and October 2, 2016, respectively	559	570
Additional paid-in capital	193,835	260,340
Accumulated other comprehensive loss	(98,500)	(128,008)
Retained earnings	832,559	736,357
Tetra Tech stockholders' equity	928,453	869,259
Noncontrolling interests	171	144
Total equity	928,624	869,403
Total liabilities and equity	$ 1,902,745	$ 1,800,779

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Oct. 01, 2017	Oct. 02, 2016
Statement of Financial Position [Abstract]
Preferred stock, authorized shares (in shares)	2,000,000	2,000,000
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, authorized shares (in shares)	150,000,000	150,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares issued (in shares)	55,873,000	57,042,000
Common stock, shares outstanding (in shares)	55,873,000	57,042,000

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Income Statement [Abstract]
Revenue	$ 2,753,360	$ 2,583,469	$ 2,299,321
Subcontractor costs	(719,350)	(654,264)	(580,606)
Other costs of revenue	(1,680,372)	(1,598,994)	(1,402,925)
Gross profit	353,638	330,211	315,790
Selling, general and administrative expenses	(177,219)	(171,985)	(170,456)
Acquisition and integration expenses	0	(19,548)	0
Contingent consideration – fair value adjustments	6,923	(2,823)	3,113
Impairment of goodwill and other intangible assets	0	0	(60,763)
Operating income	183,342	135,855	87,684
Interest income	729	996	680
Interest expense	(12,310)	(12,385)	(8,043)
Income before income tax expense	171,761	124,466	80,321
Income tax expense	(53,844)	(40,613)	(41,093)
Net income including noncontrolling interests	117,917	83,853	39,228
Net income from noncontrolling interests	(43)	(70)	(154)
Net income attributable to Tetra Tech	$ 117,874	$ 83,783	$ 39,074
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 2.07	$ 1.44	$ 0.64
Diluted (in dollars per share)	$ 2.04	$ 1.42	$ 0.64
Weighted-average common shares outstanding:
Basic (in shares)	56,911	58,186	60,913
Diluted (in shares)	57,913	58,966	61,532
Cash dividends paid per share (in dollars per share)	$ 0.38	$ 0.34	$ 0.30

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Statement of Comprehensive Income [Abstract]
Net income including noncontrolling interests	$ 117,917	$ 83,853	$ 39,228
Foreign currency translation adjustments	27,902	14,392	(98,287)
Gain (loss) on cash flow hedge valuations	1,614	774	(2,489)
Other comprehensive income (loss), net of tax	29,516	15,166	(100,776)
Comprehensive income (loss) including noncontrolling interests	147,433	99,019	(61,548)
Net income attributable to noncontrolling interests	(43)	(70)	(154)
Foreign currency translation adjustments, net of tax	(8)	(3)	143
Comprehensive income attributable to noncontrolling interests	(51)	(73)	(11)
Comprehensive income (loss) attributable to Tetra Tech	$ 147,382	$ 98,946	$ (61,559)

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Total Tetra Tech Equity	Non-Controlling Interests
Beginning balance at Sep. 28, 2014	$ 1,013,056	$ 626	$ 402,516	$ (42,538)	$ 651,475	$ 1,012,079	$ 977
Beginning balance (in shares) at Sep. 28, 2014		62,591
Comprehensive income, net of tax:
Net income	39,228				39,074	39,074	154
Foreign currency translation adjustments	(98,287)			(98,144)		(98,144)	(143)
Gain (loss) on cash flow hedge valuations	(2,489)			(2,489)		(2,489)
Comprehensive income (loss) including noncontrolling interests	(61,548)					(61,559)	11
Distributions paid to noncontrolling interests	(515)						(515)
Cash dividends of $0.30, $0.34, and $0.38 per common share for years ended September 27, 2015, October 2, 2016, and October 1, 2017, respectively.	(18,240)				(18,240)	(18,240)
Stock-based compensation	10,926		10,926			10,926
Stock options exercised	8,990	$ 5	8,985			8,990
Stock options exercised (in shares)		510
Shares issued for Employee Stock Purchase Plan	5,203	$ 3	5,200			5,203
Shares issued for Employee Stock Purchase Plan (in shares)		243
Stock repurchases	(100,500)	$ (40)	(100,460)			(100,500)
Stock repurchases (in shares)		(3,963)
Tax benefit for stock options	(574)		(574)			(574)
Ending balance at Sep. 27, 2015	856,798	$ 594	326,593	(143,171)	672,309	856,325	473
Ending balance (in shares) at Sep. 27, 2015		59,381
Comprehensive income, net of tax:
Net income	83,853				83,783	83,783	70
Foreign currency translation adjustments	14,392			14,389		14,389	3
Gain (loss) on cash flow hedge valuations	774			774		774
Comprehensive income (loss) including noncontrolling interests	99,019					98,946	73
Distributions paid to noncontrolling interests	(402)						(402)
Cash dividends of $0.30, $0.34, and $0.38 per common share for years ended September 27, 2015, October 2, 2016, and October 1, 2017, respectively.	(19,735)				(19,735)	(19,735)
Stock-based compensation	12,964		12,964			12,964
Stock options exercised	15,823	$ 9	15,814			15,823
Stock options exercised (in shares)		920
Shares issued for Employee Stock Purchase Plan	4,707	$ 2	4,705			4,707
Shares issued for Employee Stock Purchase Plan (in shares)		209
Stock repurchases	(99,500)	$ (35)	(99,465)			(99,500)
Stock repurchases (in shares)		(3,468)
Tax benefit for stock options	(271)		(271)			(271)
Ending balance at Oct. 02, 2016	869,403	$ 570	260,340	(128,008)	736,357	869,259	144
Ending balance (in shares) at Oct. 02, 2016		57,042
Comprehensive income, net of tax:
Net income	117,917				117,874	117,874	43
Foreign currency translation adjustments	27,902			27,894		27,894	8
Gain (loss) on cash flow hedge valuations	1,614			1,614		1,614
Comprehensive income (loss) including noncontrolling interests	147,433					147,382	51
Distributions paid to noncontrolling interests	(24)						(24)
Cash dividends of $0.30, $0.34, and $0.38 per common share for years ended September 27, 2015, October 2, 2016, and October 1, 2017, respectively.	(21,672)				(21,672)	(21,672)
Stock-based compensation	13,450		13,450			13,450
Stock options exercised	15,094	$ 10	15,084			15,094
Stock options exercised (in shares)		907
Shares issued for Employee Stock Purchase Plan	4,940	$ 2	4,938			4,940
Shares issued for Employee Stock Purchase Plan (in shares)		190
Stock repurchases	(100,000)	$ (23)	(99,977)			(100,000)
Stock repurchases (in shares)		(2,266)
Ending balance at Oct. 01, 2017	$ 928,624	$ 559	$ 193,835	$ (98,500)	$ 832,559	$ 928,453	$ 171
Ending balance (in shares) at Oct. 01, 2017		55,873

Consolidated Statements of Equ7

Consolidated Statements of Equity (Parenthetical) - $ / shares	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Statement of Stockholders' Equity [Abstract]
Cash dividends paid per share (in dollars per share)	$ 0.38	$ 0.34	$ 0.30

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Cash flows from operating activities:
Net income including noncontrolling interests	$ 117,917	$ 83,853	$ 39,228
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	45,756	45,588	44,201
Equity in income of unconsolidated joint ventures	(4,699)	(1,652)	(5,131)
Distributions of earnings from unconsolidated joint ventures	4,052	2,796	5,252
Stock-based compensation	13,450	12,964	10,926
Excess tax benefits from stock-based compensation	0	(918)	(172)
Deferred income taxes	(9,957)	6,051	8,412
Provision (recovery) for doubtful accounts	2,847	8,082	(1,034)
Impairment of goodwill and other intangible assets	0	0	60,763
Fair value adjustments to contingent consideration	(6,923)	2,823	(3,113)
Lease termination costs and related asset impairment	0	2,946	342
Gain on disposal of property and equipment	(103)	(537)	(6,014)
Changes in operating assets and liabilities, net of effects of business acquisitions:
Accounts receivable	(64,781)	9,062	40,345
Prepaid expenses and other assets	(8,317)	3,720	12,970
Accounts payable	18,597	(3,002)	(26,901)
Accrued compensation	13,413	8,434	(7,676)
Billings in excess of costs on uncompleted contracts	28,298	(13,874)	(10,319)
Other liabilities	2,167	(19,321)	(7,143)
Income taxes receivable/payable	(13,725)	(4,995)	7,911
Net cash provided by operating activities	137,992	142,020	162,847
Cash flows from investing activities:
Capital expenditures	(9,741)	(11,945)	(24,296)
Payments for business acquisitions, net of cash acquired	(8,039)	(81,259)	(11,680)
Changes in restricted cash	0	(2,519)	4,530
Proceeds from sale of property and equipment	905	3,076	10,426
Investments in unconsolidated joint ventures	(85)	(1,368)	0
Net cash used in investing activities	(16,960)	(94,015)	(21,020)
Cash flows from financing activities:
Payments on long-term debt	(233,865)	(148,485)	(75,459)
Proceeds from borrowings	243,553	229,049	64,794
Payments of contingent earn-out liabilities	(1,319)	(3,251)	(3,199)
Debt pre-payment costs	0	(1,935)	(1,457)
Distributions paid to noncontrolling interests	(24)	(402)	(515)
Excess tax benefits from stock-based compensation	0	918	172
Repurchases of common stock	(100,000)	(99,500)	(100,500)
Net proceeds from issuance of common stock	18,555	17,953	10,825
Dividends paid	(21,672)	(19,735)	(18,240)
Net cash used in financing activities	(94,772)	(25,388)	(123,579)
Effect of foreign exchange rate changes on cash	3,256	2,516	(5,301)
Net increase in cash and cash equivalents	29,516	25,133	12,947
Cash and cash equivalents at beginning of year	160,459	135,326	122,379
Cash and cash equivalents at end of year	189,975	160,459	135,326
Cash paid during the year for:
Interest	11,504	12,575	7,323
Income taxes, net of refunds of $2.1 million, $3.2 million and $5.4 million	$ 72,578	$ 35,273	$ 23,268

Consolidated Statements of Cas9

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Statement of Cash Flows [Abstract]
Income taxes, net of refunds received	$ 2.1	$ 3.2	$ 5.4

Description of Business

Description of Business	12 Months Ended
	Oct. 01, 2017
Description of Business
Description of Business	Description of Business We are a leading provider of consulting and engineering services that focuses on water, environment, infrastructure, resource management, energy, and international development. We are a global company that is renowned for our expertise in providing water-related services for public and private clients. We typically begin at the earliest stage of a project by identifying technical solutions and developing execution plans tailored to our clients' needs and resources. Our solutions may span the entire life cycle of consulting and engineering projects and include applied science, data analysis, research, engineering, design, construction management, and operations and maintenance. In fiscal 2017 , we managed our operations under three reportable segments. We report our water resources, water and wastewater treatment, environment, and infrastructure engineering activities in the Water, Environment and Infrastructure ("WEI") reportable segment. Our Resource Management and Energy ("RME") reportable segment includes our oil and gas, energy, international development, waste management, remediation, and utilities services. In addition, we report the results of the wind-down of our non-core construction activities in the Remediation and Construction Management ("RCM") reportable segment.

Basis of Presentation and Prepa

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

Stock Repurchase and Dividends

Stock Repurchase and Dividends	12 Months Ended
	Oct. 01, 2017
Stock Repurchase and Dividends
Stock Repurchase and Dividends	Stock Repurchase and Dividends On November 7, 2016, the Board of Directors authorized a new stock repurchase program under which we could repurchase up to $200 million of our common stock. In fiscal 2017 , we repurchased through open market purchases under this program a total of 2,266,397 shares at an average price of $44.12 for a total cost of $ 100.0 million . On November 7, 2016, the Board of Directors declared a quarterly cash dividend of $0.09 per share payable on December 14, 2016 to stockholders of record as of the close of business on December 1, 2016. On January 30, 2017, the Board of Directors declared a quarterly cash dividend of $0.09 per share payable on March 3, 2017 to stockholders of record as of the close of business on February 17, 2017. On May 1, 2017, the Board of Directors declared a quarterly cash dividend of $0.10 per share payable on June 2, 2017 to stockholders of record as of the close of business on May 18, 2017. On July 31, 2017, the Board of Directors declared a quarterly cash dividend of $0.10 per share payable on September 1, 2017 to stockholders of record as of the close of business on August 17, 2017. Dividends totaling 21.7 million and $ 19.7 million were paid in fiscal 2017 and 2016 , respectively. Subsequent Events. On November 6, 2017, the Board of Directors declared a quarterly cash dividend of $0.10 per share payable on December 15, 2017 to stockholders of record as of the close of business on November 30, 2017.

Accounts Receivable - Net and R

Accounts Receivable - Net and Revenue Recognition	12 Months Ended
	Oct. 01, 2017
Accounts Receivable - Net and Revenue Recognition
Accounts Receivable - Net and Revenue Recognition	Accounts Receivable – Net and Revenue Recognition Net accounts receivable and billings in excess of costs on uncompleted contracts consisted of the following at October 1, 2017 and October 2, 2016 : October 1, October 2, (in thousands) Billed $ 376,287 $ 364,287 Unbilled 404,899 356,147 Contract retentions 39,840 29,135 Total accounts receivable – gross 821,026 749,569 Allowance for doubtful accounts (32,259 ) (35,233 ) Total accounts receivable – net $ 788,767 $ 714,336 Billings in excess of costs on uncompleted contracts $ 117,499 $ 88,223 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. Except for amounts related to claims as discussed below, most of our unbilled receivables at October 1, 2017 are expected to be billed and collected within 12 months. Contract retentions represent amounts withheld by clients until certain conditions are met or the project is completed, which may be several months or years. The allowance for doubtful accounts represents amounts that are expected to 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 revenue recognized. The majority of billings in excess of costs on uncompleted contracts will be earned within 12 months. 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 result in "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 a definitive client agreement. Unapproved change orders constitute claims in excess of agreed contract prices that we seek to collect from our clients for delays, errors in specifications and designs, contract terminations, or other causes of unanticipated additional costs. Revenue on claims is recognized when contract costs related to claims have been incurred and when their addition to contract value can be reliably estimated. This can lead to a situation in which costs are recognized in one period and revenue is recognized in a subsequent period, such as when client agreement is obtained or a claims resolution occurs. Total accounts receivable at October 1, 2017 and October 2, 2016 included $59 million and $45 million , respectively, related to claims, including requests for equitable adjustment, on contracts that provide for price redetermination. We regularly evaluate all unsettled claim amounts and record appropriate adjustments to operating earnings when it is probable that the claim will result in a different contract value than the amount previously estimated. As a result of this assessment, in fiscal 2017 , we recognized a reduction of revenue of $4.9 million and related losses in operating income of $3.6 million in our RCM segment. In fiscal 2016 , we collected $13.4 million to settle claims of $8.8 million , which resulted in gains in operating income of $4.6 million in the RCM segment. In fiscal 2016, we also recognized reductions in operating income in our RCM segment and a related increase in the allowance for doubtful accounts of $7.9 million as a result of our updated assessment of the collectability of certain accounts receivable, of which $4.6 million related to unsettled claims. Related to these same projects, we have claims and potential claims against us from both our subcontractors and customers for back charges. We believe these claims are without merit and thus any liability is considered remote at this time. However, changes in these estimates could result in the recognition of additional project costs and losses in the period when changes to estimate are made. Billed accounts receivable related to U.S. federal government contracts were $45.4 million and $47.4 million at October 1, 2017 and October 2, 2016 , respectively. U.S. federal government contracts unbilled receivables were $109.7 million and $92.2 million at October 1, 2017 and October 2, 2016 , respectively. Other than the U.S. federal government, no single client accounted for more than 10% of our accounts receivable at October 1, 2017 and October 2, 2016 . We recognize revenue for most of our contracts using the percentage-of-completion method, primarily utilizing the cost-to-cost approach, to estimate the progress towards completion in order to determine the amount of revenue and profit to recognize. Changes in those estimates could result in the 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. As a result, we recognized net unfavorable operating income adjustments of $8.0 million ( $2.3 million in the RME segment and $5.7 million in the RCM segment) during fiscal 2017. We recognized net unfavorable operating income adjustments during fiscal 2016 of $2.3 million (all in the RCM segment) and during fiscal 2015 of $8.9 million . Changes in revenue and cost estimates could also result in a projected loss that would be recorded immediately in earnings. As of October 1, 2017 and October 2, 2016 , our consolidated balance sheets included liabilities for anticipated losses of $8.1 million and $6.7 million , respectively. The estimated cost to complete the related contracts as of October 1, 2017 was $5.0 million .

Mergers and Acquisitions

Mergers and Acquisitions	12 Months Ended
	Oct. 01, 2017
Business Combinations [Abstract]
Mergers and Acquisitions	Mergers and Acquisitions In fiscal 2015, we acquired Cornerstone Environmental Group, LLC ("CEG"), headquartered in Middletown, New York. CEG is an environmental engineering and consulting firm focused on solid waste markets in the United States, and is included in our RME segment. The fair value of the purchase price for CEG was $15.9 million . Of this amount, $11.8 million was paid to the former owners and $4.1 million was the estimated fair value of contingent earn-out obligations, with a maximum of $9.8 million , based upon the achievement of specified financial objectives. The results of this acquisition were included in the consolidated financial statements from the closing date. The acquisition was not considered material to our consolidated financial statements. As a result, no pro forma information has been provided. In the second quarter of fiscal 2016, we acquired control of Coffey International Limited ("Coffey"), headquartered in Sydney, Australia. Coffey had approximately 3,300 staff delivering technical and engineering solutions in international development and geoscience. Coffey significantly expands our geographic presence, particularly in Australia and Asia Pacific, and is part of our RME segment. In addition to Australia, Coffey's international development business has operations supporting federal government agencies in the U.S., Australia and the United Kingdom. The fair value of the purchase price for Coffey was $76.1 million , in addition to $65.1 million of assumed debt, which consisted of secured bank term debt of $37.1 million and unsecured corporate bond obligations of $28.0 million . All of this debt was paid in full in the second quarter of fiscal 2016 subsequent to the acquisition. In the second quarter of fiscal 2016, we also acquired INDUS Corporation ("INDUS"), headquartered in Vienna, Virginia. INDUS is an information technology solutions firm focused on water data analytics, geospatial analysis, secure infrastructure, and software applications management for U.S. federal government customers, and is included in our WEI segment. The fair value of the purchase price for INDUS was $18.7 million . Of this amount, $14.0 million was paid to the sellers and $4.7 million was the estimated fair value of contingent earn-out obligations, with a maximum of $8.0 million , based upon the achievement of specified operating income targets in each of the two years following the acquisition. In the second quarter of fiscal 2017, we completed the acquisition of Eco Logical Australia (“ELA”), headquartered in Sydney, Australia. ELA is a multi-disciplinary consulting firm with over 160 staff that provides innovative, high-end environmental and ecological services, and is part of our RME segment. The fair value of the purchase price for ELA was $9.9 million . Of this amount, $8.3 million was paid to the sellers and $1.6 million was the estimated fair value of contingent earn-out obligations, with a maximum of $1.7 million , based upon the achievement of specified operating income targets in each of the two years following the acquisition. The following table summarizes the estimated fair values of assets acquired and liabilities assumed as of the respective acquisition dates for our acquisitions completed in fiscal 2016 (in thousands): Accounts receivable $ 71,515 Other current assets 18,869 Property and equipment 14,218 Goodwill 108,323 Backlog and trade name intangible assets 29,445 Other assets 747 Current liabilities (78,311 ) Borrowings (65,086 ) Other long-term liabilities (4,885 ) Net assets acquired $ 94,835 Goodwill additions resulting from the above business combinations are primarily attributable to the existing workforce of the acquired companies and the synergies expected to arise after the acquisitions. The goodwill addition related to the fiscal 2017 acquisition primarily represents the value of a workforce with distinct expertise in the environmental and ecological markets. The goodwill additions related to the fiscal 2016 acquisitions primarily represent the value of workforces with distinct expertise in the international development, geoscience, and software applications management markets. In addition, these acquired capabilities, when combined with our existing global consulting and engineering business, result in opportunities that allow us to provide services under contracts that could not have been pursued individually by either us or the acquired companies. The results of these acquisitions were included in the consolidated financial statements from their respective closing dates. Backlog and trade name intangible assets include the fair value of existing contracts and the underlying customer relationships with lives ranging from 1 to 5 years (weighted average of approximately 3 years) and the fair value of trade names with lives ranging from 3 to 5 years. The table below presents summarized unaudited consolidated pro forma operating results including the related acquisition, integration and debt pre-payment charges, assuming we had acquired Coffey and INDUS at the beginning of fiscal 2016 . These pro-forma operating results are presented for illustrative purposes only and are not indicative of the operating results that would have been achieved had the related events occurred at the beginning of fiscal 2016 . Pro-Forma Fiscal Year Ended October 1, October 2, (in thousands, except per share data) Revenue $ 2,753,360 $ 2,714,658 Operating income 183,342 152,676 Net income attributable to Tetra Tech 117,874 98,871 Earnings per share attributable to Tetra Tech Basic $ 2.07 $ 1.70 Diluted $ 2.04 $ 1.68 Acquisition and integration expenses in the accompanying consolidated statements of income are comprised of the following: Fiscal Year Ended (in thousands) Severance including change in control payments $ 10,917 Professional services 5,685 Real estate-related 2,946 Total $ 19,548 As of October 2, 2016 , all of the acquisition and integration expenses incurred to date had been paid. All acquisition and integration expenses are included in our Corporate reportable segment, as presented in Note 18 , " Reportable Segments " . In addition, in the second quarter of fiscal 2016 , we repaid Coffey's bank loans and corporate bonds in full, including $1.9 million in pre-payment charges that are included in interest expense. Most of our acquisition agreements include contingent earn-out agreements, which are generally based on the achievement of future operating income thresholds. The contingent earn-out arrangements are based on 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 any 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 contingent earn-out 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 contingent earn-out liability on the acquisition date is reflected as cash used in operating activities in our consolidated statements of cash flows. 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. During fiscal 2017, we recorded adjustments to our contingent earn-out liabilities and reported related net gains in operating income totaling $6.9 million . These gains resulted from updated valuations of the contingent consideration liabilities for INDUS and CEG. During fiscal 2016, we increased our contingent earn-out liabilities and reported related losses in operating income of $2.8 million . These losses include a $1.8 million charge that reflected our updated valuation of the contingent consideration liability for CEG. This valuation included our updated projection of CEG's financial performance during the earn-out period, which exceeded our original estimate at the acquisition date. The remaining $1.0 million loss represented the final cash settlement of an earn-out liability that was valued at $0 at the end of fiscal 2015. The acquisition agreement for INDUS included a contingent earn-out agreement based on the achievement of operating income thresholds in each of the first two years beginning on the acquisition date, which was in the second quarter of fiscal 2016. The maximum earn-out obligation over the two -year earn-out period was $8.0 million ( $4.0 million in each year). These amounts could be earned on a pro-rata basis starting at 50% of the earn-out maximum for operating income within a predetermined range in each year. INDUS was required to meet a minimum operating income threshold in each year to earn any contingent consideration. These minimum thresholds were $3.2 million and $3.6 million in years one and two, respectively. In order to earn the maximum contingent consideration, INDUS needed to generate operating income of $3.6 million in year one and $4.0 million in year two. The determination of the fair value of the purchase price for INDUS on the acquisition date included our estimate of the fair value of the related contingent earn-out obligation. The initial valuation was primarily based on probability-weighted internal estimates of INDUS’ operating income during each earn-out period. As a result of these estimates, we calculated an initial fair value at the acquisition date of INDUS’ contingent earn-out liability of $4.7 million in the second quarter of fiscal 2016. This amount had increased to $4.9 million at the end of fiscal 2016 due to the passage of time for the present value calculation. In determining that INDUS would earn 59% of the maximum potential earn-out, we considered several factors including INDUS’ recent historical revenue and operating income levels and growth rates. We also considered the recent trend in INDUS’ backlog level. INDUS’ actual financial performance in the first earn-out period was below our original expectation at the acquisition date. As a result, in the second quarter of fiscal 2017, we evaluated our estimate of INDUS’ contingent consideration liability for both earn-out periods. This assessment included a review of INDUS’ financial results in the first earn-out period, the status of ongoing projects in INDUS’ backlog, and the inventory of prospective new contract awards. As a result of this assessment, we concluded that INDUS’ operating income in both the first and second earn-out periods would be lower than the minimum requirements of $3.2 million and $3.6 million , respectively, to earn any contingent consideration. Accordingly, in the second quarter of fiscal 2017, we reduced the INDUS contingent earn-out liability to $0 , which resulted in a gain of $5.0 million . The acquisition agreement for CEG included a contingent earn-out agreement based on the achievement of operating income thresholds in each of the first three years beginning on the acquisition date, which was in the third quarter of fiscal 2015. The maximum earn-out obligation over the three -year earn-out period was $9.8 million ( $3.25 million in each year). The annual amounts could be earned primarily on a pro-rata basis for operating income within a predetermined range in each year. To a lesser extent, additional earn-out consideration could be earned for operating income above the high-end of the range up to the contractual maximum of $9.8 million . CEG was required to meet a minimum operating income threshold in each year to earn any contingent consideration. These minimum thresholds were $2.0 million , $2.3 million and $2.6 million in years one, two and three, respectively. In order to earn the maximum contingent consideration, CEG needed to achieve operating income of $4.5 million in year one, $4.8 million in year two and $5.1 million in year three. The determination of the fair value of the purchase price for CEG on the acquisition date included our estimate of the fair value of the related contingent earn-out obligation. The initial valuation was primarily based on probability-weighted internal estimates of CEG’s operating income during each earn-out period. As a result of these estimates, we calculated an initial fair value at the acquisition date of CEG’s contingent earn-out liability of $4.1 million in the third quarter of fiscal 2015. In determining that CEG would earn 42% of the maximum potential earn-out, we considered several factors including CEG’s recent historical revenue and operating income levels and growth rates. We also considered the recent trend in CEG’s backlog level. In the second quarter of fiscal 2016, we recorded an increase in our contingent earn-out liabilities and related losses in operating income of $1.8 million , which reflected our updated valuation of the contingent consideration liability for CEG. This valuation included our updated projection of CEG’s financial performance during the earn-out period, which exceeded our original estimate at the acquisition date. The first earn-out payment of $2.3 million was made in the fourth quarter of fiscal 2016, at which time a $3.9 million contingent consideration liability remained for the last two years of CEG’s earn-out period. During the second quarter of fiscal 2017, we evaluated our estimate of CEG’s contingent consideration liability for the remaining two earn-out periods. This assessment included a review of CEG’s financial results to-date in the second earn-out period, the status of ongoing projects in CEG’s backlog, and the inventory of prospective new contract awards. As a result of this assessment, we concluded that CEG’s operating income in both the second and third earn-out periods would be lower than our previous estimate. Accordingly, we reduced the CEG contingent earn-out liability to $1.8 million as of April 2, 2017, which resulted in a gain of $2.1 million in the second quarter of fiscal 2017. The second earn-out payment of $1.3 million was made in the fourth quarter of fiscal 2017. During the second quarter of fiscal 2017, when we determined that INDUS’ and CEG’s operating income would be lower than our previous estimates, including our original estimates at the acquisition dates, we also evaluated the related goodwill for potential impairment. In each case, we determined that the related reporting units’ long-term performance was not materially impacted and there was no resulting goodwill impairment. During fiscal 2016, we also recognized a $1.0 million loss, which represented the final cash settlement of an earn-out liability that was valued at $0 at the end of fiscal 2015. During fiscal 2015, we decreased our contingent earn-out liabilities and reported a related gain in operating income of $3.1 million . This gain resulted from an updated valuation of the contingent consideration liability for Caber Engineering Inc. ("Caber"), which is part of our RME segment. The acquisition agreement for Caber included a contingent earn-out agreement based on the achievement of operating income thresholds (in Canadian dollars) in each of the first two years beginning on the acquisition date, which was in the first quarter of fiscal 2014. The maximum earn-out obligation over the two -year earn-out period was C$8.0 million ( C$4.0 million in each year). These amounts could be earned on a pro-rata basis for operating income within a predetermined range in each year. Caber was required to meet a minimum operating income threshold in each year to earn any contingent consideration. These thresholds were C$4.0 million and C$4.6 million in years one and two, respectively. In order to earn the maximum contingent consideration, Caber needed to generate operating income of C$4.4 million in year one and C$5.1 million in year two. The determination of the fair value of the purchase price for Caber on the acquisition date included our estimate of the fair value of the related contingent earn-out obligation. This initial valuation was primarily based on probability-weighted internal estimates of Caber's operating income during each earn-out period. As a result of these estimates, we calculated an initial fair value at the acquisition date of Caber's contingent earn-out liability of C$6.5 million in the first quarter of fiscal 2014. In determining that Caber would earn 81% of the maximum potential earn-out, we considered several factors including Caber's recent historical revenue and operating income levels and growth rates. We also considered the recent trend in Caber's backlog level and the prospects for the oil and gas industry in Western Canada. Caber's actual financial performance in the first earn-out period exceeded our original estimate at the acquisition date. As a result, in the fourth quarter of fiscal 2014, we increased the related contingent consideration liability and recognized a loss of $1.0 million . This updated valuation included our assumption that Caber would earn the maximum amount of contingent consideration of $4.0 million in the first earn-out period. In the second quarter of fiscal 2015, we completed our final calculation of the contingent consideration for the first earn-out period and paid contingent consideration of C$4.0 million (USD $3.2 million ). At that time we also evaluated our estimate of Caber's contingent consideration liability for the second earn-out period. This assessment included a review of the status of ongoing projects in Caber's backlog, and the inventory of prospective new contract awards. We also considered the status of the oil and gas industry in Western Canada, particularly in light of the decline in oil prices at the time. As a result of this assessment, we concluded that Caber's operating income in the second earn-out period would be lower than our original estimate at the acquisition date and our subsequent estimates through the first quarter of fiscal 2015. We also concluded that Caber's operating income for the second earn-out period would be lower than the minimum requirement of C$4.6 million to earn any contingent consideration. Accordingly, in the second quarter of fiscal 2015, we reduced the Caber contingent earn-out liability to $0 , which resulted in a gain of $3.1 million . The second earn-out period ended in the first quarter of fiscal 2016 with no further adjustments. At October 1, 2017 , there was a total maximum of $8.9 million of outstanding contingent consideration related to acquisitions. Of this amount, $2.4 million was estimated as the fair value and accrued on our consolidated balance sheet. The following table summarizes the changes in the carrying value of estimated contingent earn-out liabilities: Fiscal Year Ended October 1, October 2, September 27, (in thousands) Beginning balance (at fair value) $ 8,757 $ 4,169 $ 7,030 Estimated earn-out liabilities for acquisitions during the fiscal year 1,604 4,745 4,100 Increases due to re-measurement of fair value reported in interest expense 260 271 136 Net increase (decrease) due to re-measurement of fair value reported as losses (gains) in operating income (6,923 ) 2,823 (3,113 ) Foreign exchange impact 59 — (785 ) Earn-out payments: Reported as cash used in operating activities — — — Reported as cash used in financing activities (1,319 ) (3,251 ) (3,199 ) Ending balance (at fair value) $ 2,438 $ 8,757 $ 4,169 Subsequent Event. On October 2, 2017, we acquired Glumac, a leader in sustainable infrastructure design. The company has more than 300 employees and incorporates innovative sustainable technologies and solutions into each of its designs, including the design and engineering of Leadership in Energy and Environmental Design (LEED) standard and Net-Zero infrastructure .

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Oct. 01, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets The following table summarizes the changes in the carrying value of goodwill: WEI RME Total (in thousands) Balance at September 27, 2015 $ 210,748 $ 390,631 $ 601,379 Goodwill additions 9,080 98,538 107,618 Goodwill adjustments — 1,687 1,687 Foreign exchange translation 2,125 5,179 7,304 Balance at October 2, 2016 221,953 496,035 717,988 Goodwill additions — 7,055 7,055 Goodwill adjustments 13,509 (12,804 ) 705 Foreign exchange translation 6,273 8,865 15,138 Balance at October 1, 2017 $ 241,735 $ 499,151 $ 740,886 We perform our annual goodwill impairment review at the beginning of our fiscal fourth quarter. Our last review at July 3, 2017 (i.e. the first day of our fourth quarter in fiscal 2017 ), indicated that we had no impairment of goodwill, and all of our reporting units had estimated fair values that were in excess of their carrying values, including goodwill. We had no reporting units that had estimated fair values that exceeded their carrying values by less than 20% . In addition, we regularly evaluate whether events and circumstances have occurred that may indicate a potential change in the recoverability of goodwill. We perform interim goodwill impairment reviews between our annual reviews if certain events and circumstances have occurred, such as a deterioration in general economic conditions; an increase in the 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. In the fourth quarter of fiscal 2015, the mining sector continued to contract in response to lower global growth expectations driven in large part by China's actual and projected slower economic growth. Consistent with this trend, our mining customers continued their curtailment of capital spending for new mining projects. As a result, our Global Mining Practice ("GMP") reporting unit experienced a 25% decline in revenue in the fourth quarter of fiscal 2015 compared to the same period of fiscal 2014. This negative trend was compared to the expected revenue growth of approximately 3% in the previous goodwill impairment test, performed as of June 30, 2014. In response to these results, we performed a strategic review of GMP in the fourth quarter of fiscal 2015, and determined that our mining activities would likely decline further in fiscal 2016, and that revenue and profits would not return to acceptable levels of performance in the foreseeable future. We also decided to redeploy a significant portion of our mining resources into other operational areas that have better growth and profitability prospects. Consequently, as of the first day of fiscal 2016, GMP was no longer a reporting unit. We considered GMP's financial performance and prospects in our goodwill impairment analysis in the fourth quarter of fiscal 2015 and determined that GMP's fair value had fallen significantly below its carrying value, including goodwill. As required, we performed further analysis to measure the amount of the impairment loss and, as a result, we wrote-off all of GMP's goodwill and identifiable intangible assets and recorded a related impairment charge of $60.8 million ( $57.3 million after-tax) in the fourth quarter of fiscal 2015. The related goodwill and identifiable intangible assets that were determined not to be recoverable totaled $58.1 million and $2.7 million , respectively. Our fourth quarter 2017 and 2016 goodwill impairment reviews indicated that we had no other impairment of goodwill, and all of our other reporting units had estimated fair values that were in excess of their carrying values, including goodwill. Although we believe that our estimates of fair value for these reporting units are reasonable, if financial performance for these reporting units falls significantly below our expectations or market prices for similar business decline, the goodwill for these reporting units could become impaired. Foreign exchange translation relates to our foreign subsidiaries with functional currencies that are different than our reporting currency. The gross amounts of goodwill for WEI were $324.1 million and $304.4 million at October 1, 2017 and October 2, 2016 , respectively, excluding $82.4 million of accumulated impairment. The gross amounts of goodwill for RME were $532.4 million and $529.2 million at October 1, 2017 and October 2, 2016 , respectively, excluding $33.2 million of accumulated impairment. The gross amount and accumulated amortization of our acquired identifiable intangible assets with finite useful lives included in "Intangible assets – net" on the consolidated balance sheets, were as follows: Fiscal Year Ended October 1, 2017 October 2, 2016 Weighted- Average Remaining Life (in years) Gross Amount Accumulated Amortization Gross Amount Accumulated Amortization ($ in thousands) Non-compete agreements 0.1 $ 495 $ (493 ) $ 881 $ (840 ) Client relations 2.9 90,297 (75,074 ) 112,367 (83,514 ) Backlog 1.4 21,518 (13,301 ) 23,018 (7,536 ) Technology and trade names 3.3 6,685 (3,439 ) 7,778 (3,192 ) Total $ 118,995 $ (92,307 ) $ 144,044 $ (95,082 ) Foreign currency translation adjustments reduced net identifiable intangible assets by $0.1 million and $1.1 million in fiscal 2017 and 2016, respectively. Amortization expense for the identifiable intangible assets for fiscal 2017 , 2016 and 2015 was $22.8 million , $22.1 million and $20.2 million , respectively. Estimated amortization expense for the succeeding five years and beyond is as follows: Amount (in thousands) 2018 $ 14,548 2019 7,034 2020 2,802 2021 1,664 2022 411 Beyond 229 Total $ 26,688

Property and Equipment

Property and Equipment	12 Months Ended
	Oct. 01, 2017
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and Equipment Property and equipment consisted of the following: Fiscal Year Ended October 1, October 2, (in thousands) Land and buildings $ 3,680 $ 3,683 Equipment, furniture and fixtures 150,026 180,750 Leasehold improvements 27,689 30,261 Total property and equipment 181,395 214,694 Accumulated depreciation (124,560 ) (146,867 ) Property and equipment, net $ 56,835 $ 67,827 The depreciation expense related to property and equipment was $22.2 million , $22.8 million and $23.1 million for fiscal 2017 , 2016 and 2015 , respectively.

Income Taxes

Income Taxes	12 Months Ended
	Oct. 01, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The income before income taxes, by geographic area, was as follows: Fiscal Year Ended October 1, October 2, September 27, (in thousands) Income before income taxes: United States $ 166,074 $ 113,576 $ 118,822 Foreign 5,687 10,890 (38,501 ) Total income before income taxes $ 171,761 $ 124,466 $ 80,321 Income tax expense consisted of the following: Fiscal Year Ended October 1, October 2, September 27, (in thousands) Current: Federal $ 45,604 $ 22,277 $ 23,836 State 8,860 5,634 5,072 Foreign 9,337 6,651 3,773 Total current income tax expense 63,801 34,562 32,681 Deferred: Federal (4,251 ) 6,231 7,218 State (945 ) (16 ) 2,335 Foreign (4,761 ) (164 ) (1,141 ) Total deferred income tax expense (9,957 ) 6,051 8,412 Total income tax expense $ 53,844 $ 40,613 $ 41,093 Total income tax expense was different from the amount computed by applying the U.S. federal statutory rate to pre-tax income as follows: Fiscal Year Ended October 1, October 2, September 27, Tax at federal statutory rate 35.0% 35.0% 35.0% State taxes, net of federal benefit 3.4 3.1 5.0 Research and Development ("R&D") credit (1.8) (3.4) (3.8) Domestic production deduction (0.7) (0.7) (0.8) Tax differential on foreign earnings — (1.6) (3.8) Non-taxable foreign interest income (2.9) (3.9) (5.9) Non-deductible executive compensation — 2.0 — Goodwill and contingent consideration — — 19.2 Stock compensation (2.8) 0.3 0.5 Valuation allowance (0.5) 2.4 5.7 Change in uncertain tax positions 1.8 (2.0) — Other (0.2) 1.4 0.1 Total income tax expense 31.3% 32.6% 51.2% The effective tax rates for fiscal 2017 and 2016 were 31.3% and 32.6% , respectively. During fiscal 2017, we adopted accounting guidance which requires excess tax benefits and deficiencies on share-based payments to be recorded as an income tax benefit or expense, respectively, in the statement of income rather than being recorded in additional paid-in capital on the balance sheet. As a result, we recognized an income tax benefit of $4.9 million in fiscal 2017. Excluding this items, the effective tax rate for fiscal 2017 was 34.2% . In fiscal 2017, the Internal Revenue Service (“IRS”) concluded their examination for fiscal years 2010 through 2013, and we recognized a related $1.2 million tax benefit in fiscal 2017. Additionally, as a result of prior-year tax examinations, we made payments to tax authorities totaling approximately $23 million in fiscal 2017. In fiscal 2016, we incurred $13.3 million of acquisition and integration expenses and debt pre-payment fees for which no tax benefit was recognized. Of this amount, $6.4 million resulted from acquisition expenses that were not tax deductible and $6.9 million resulted from integration expenses and debt pre-payment fees incurred in jurisdictions with current and historical net operating losses where the related deferred tax asset was fully reserved. Additionally, during the first quarter of fiscal 2016, the Protecting Americans from Tax Hikes Act of 2015 was signed into law which permanently extended the R&D credit retroactive to January 1, 2015. Our income tax expense for fiscal 2016 included an income tax benefit of $2.0 million attributable to operating income during the last nine months of fiscal 2015, primarily related to the retroactive recognition of the R&D credit. Excluding these items, the effective tax rate for fiscal 2016 was 30.9% . We are currently under examination by the Internal Revenue Service for fiscal years 2014 through 2016, and by the California Franchise Tax Board for fiscal years 2004 through 2009. We are also subject to various other state audits. With a few exceptions, we are no longer subject to U.S. federal, state and local, or non-U.S. income tax examinations for fiscal years before 2010. Temporary differences comprising the net deferred income tax liability shown on the accompanying consolidated balance sheets were as follows: Fiscal Year Ended October 1, October 2, (in thousands) Deferred Tax Assets: State taxes $ 598 $ 697 Reserves and contingent liabilities 2,941 2,539 Allowance for doubtful accounts 4,273 3,817 Accrued liabilities 22,466 24,663 Stock-based compensation 10,069 10,684 Intangibles — — Loss carry-forwards 28,261 23,514 Valuation allowance (25,326 ) (25,447 ) Total deferred tax assets 43,282 40,467 Deferred Tax Liabilities: Unbilled revenue (46,408 ) (54,638 ) Prepaid expense (6,253 ) (2,921 ) Intangibles (24,328 ) (33,268 ) Property and equipment (8,311 ) (9,358 ) Total deferred tax liability (85,300 ) (100,185 ) Net deferred tax liabilities $ (42,018 ) $ (59,718 ) At October 1, 2017, undistributed earnings of our foreign subsidiaries, primarily in Canada, amounting to approximately $68.4 million are expected to be permanently reinvested. Accordingly, no provision for U.S. income taxes or foreign withholding taxes has been made. Upon distribution of those earnings, we would be subject to U.S. income taxes and foreign withholding taxes. Assuming the permanently reinvested foreign earnings were repatriated under the laws and rates applicable at October 1, 2017, the incremental federal tax applicable to those earnings would be approximately $6.2 million . At October 1, 2017, we had available unused state net operating loss ("NOL") carry forwards of $43.7 million that expire at various dates from 2023 to 2036; and available foreign NOL carry forwards of $92.9 million , of which $28.8 million expire at various dates from 2023 to 2037, and $64.0 million have no expiration date. We have performed an assessment of positive and negative evidence regarding the realization of the deferred tax assets. This assessment included the evaluation of scheduled reversals of deferred tax liabilities, availability of carrybacks, cumulative losses in recent years, and estimates of projected future taxable income. Although realization is not assured, based on our assessment, we have concluded that it is more likely than not that the assets will be realized except for the assets related to the loss carry-forwards and certain foreign intangibles for which a valuation allowance of $25.3 million has been provided. At October 1, 2017, we had $9.3 million of unrecognized tax benefits. Included in the balance of unrecognized tax benefits at the end of fiscal year 2017 were $9.3 million of tax benefits that, if recognized, would affect our effective tax rate. It is not expected that there will be a significant change in the unrecognized tax benefits in the next 12 months. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: Fiscal Year Ended October 1, October 2, September 27, (in thousands) Beginning balance $ 22,786 $ 21,618 $ 21,717 Additions for current year tax positions 1,060 2,802 1,147 Additions for prior year tax positions 2,365 1,466 2,309 Reductions for prior year tax positions (6,875 ) (3,100 ) (23 ) Settlements (9,999 ) — (3,532 ) Ending balance $ 9,337 $ 22,786 $ 21,618 We recognize potential interest and penalties related to unrecognized tax benefits in income tax expense. During fiscal years 2017 and 2016, we accrued additional interest expense of $0.4 million $0.2 million , respectively, and recorded reductions in accrued interest of $0.9 million and $0 million , respectively, as a result of audit settlements and other prior-year adjustments. The amount of interest and penalties accrued at October 1, 2017 and October 2, 2016 was $1.1 million and $1.0 million , respectively.

Long-Term Debt

Long-Term Debt	12 Months Ended
	Oct. 01, 2017
Debt Disclosure [Abstract]
Long-Term Debt	Long-Term Debt Long-term debt consisted of the following: Fiscal Year Ended October 1, October 2, (in thousands) Credit facilities $ 356,438 $ 346,813 Other 433 198 Total long-term debt 356,871 347,011 Less: Current portion of long-term debt (15,588 ) (15,510 ) Long-term debt, less current portion $ 341,283 $ 331,501 On May 7, 2013, we entered into a credit agreement that provided for a $205 million term loan facility and a $460 million revolving credit facility that was scheduled to mature in May 2018. On May 29, 2015, we entered into a third amendment to our credit agreement (as amended, the "Credit Agreement") that extended the maturity date for these facilities to May 2020. The Credit Agreement is a $654.8 million senior secured, five -year facility that provides for a $194.8 million term loan facility (the "Term Loan Facility") and a $460 million revolving credit facility (the "Revolving Credit Facility"). The Credit Agreement allows us to, among other things, finance certain permitted open market repurchases of our common stock, permitted acquisitions, and cash dividends and distributions. The Revolving Credit Facility includes a $150 million sublimit for the issuance of standby letters of credit, a $20 million sublimit for swingline loans, and a $150 million sublimit for multicurrency borrowings. The interest rate provisions of the Term Loan Facility and the Revolving Credit Facility did not materially change. The Term Loan Facility is subject to quarterly amortization of principal, with $10.3 million payable in year 1, and $15.4 million payable in years 2 through 5. The Term Loan may be prepaid at any time without penalty. We may borrow on the Revolving Credit Facility, at our option, at either (a) a Eurocurrency rate plus a margin that ranges from 1.15% to 2.00% per annum, or (b) a base rate for loans in U.S. dollars (the highest of the U.S. federal funds rate plus 0.50% per annum, the bank's prime rate or the Eurocurrency rate plus 1.00% ) plus a margin that ranges from 0.15% to 1.00% per annum. In each case, the applicable margin is based on our Consolidated Leverage Ratio, calculated quarterly. The Term Loan Facility is subject to the same interest rate provisions. The interest rate of the Term Loan Facility at the date of inception was 1.57% . The Credit Agreement expires on May 29, 2020 , or earlier at our discretion upon payment in full of loans and other obligations. As of October 1, 2017 , we had $356.4 million in outstanding borrowings under the Credit Agreement, which was comprised of $161.4 million under the Term Loan Facility and $195.0 million under the Revolving Credit Facility at a weighted-average interest rate of 2.45% per annum. In addition, we had $0.9 million in standby letters of credit under the Credit Agreement. Our average effective weighted-average interest rate on borrowings outstanding at October 1, 2017 under the Credit Agreement, including the effects of interest rate swap agreements described in Note 14, "Derivative Financial Instruments", was 2.65% . At October 1, 2017 , we had $264.0 million of available credit under the Revolving Credit Facility, all of which could be borrowed without a violation of our debt covenants. In addition, we entered into agreements with four banks to issue standby letters of credit. The aggregate amount of standby letters of credit outstanding under these additional agreements and other bank guarantees was $23.9 million , of which $4.9 million was issued in currencies other than the U.S. dollar. The Credit Agreement contains certain affirmative and restrictive covenants, and customary events of default. The financial covenants provide for a maximum Consolidated Leverage Ratio of 3.00 to 1.00 (total funded debt/EBITDA, as defined in the Credit Agreement) and a minimum Consolidated Fixed Charge Coverage Ratio of 1.25 to 1.00 (EBITDA, as defined in the Credit Agreement minus capital expenditures/cash interest plus taxes plus principal payments of indebtedness including capital leases, notes and post-acquisition payments). At October 1, 2017 , we were in compliance with these covenants with a consolidated leverage ratio of 1.62 x and a consolidated fixed charge coverage ratio of 2.27 x. Our obligations under the Credit Agreement are guaranteed by certain of our subsidiaries and are secured by first priority liens on (i) the equity interests of certain of our subsidiaries, including those subsidiaries that are guarantors or borrowers under the Credit Agreement, and (ii) our accounts receivable, general intangibles and intercompany loans, and those of our subsidiaries that are guarantors or borrowers. At the time of the acquisition, Coffey had an existing secured credit facility with a bank, comprised of an overdraft facility, a term facility and a bank guaranty facility. This facility was amended in March 2016 to extend the term to April 2016, and allow for the issuance of a parent guarantee and release of certain subsidiary guarantors. The facility was amended again to provide for a secured AUD $30 million facility, which may be used by Coffey for bank overdrafts, short-term cash advances or bank guarantees. This facility expired in April 2017, and prior to its expiration, a new facility was entered into with a new bank to provide for an AUD $30 million facility, which may be used by Coffey for bank overdrafts, short-term cash advances or bank guarantees. This facility expires in March 2019 and is secured by a parent guarantee. At October 1, 2017 , there were no borrowings outstanding under this facility; bank guarantees outstanding were $5.6 million , which was issued in currencies other than the U.S. dollar. The following table presents scheduled maturities of our long-term debt: Amount (in thousands) 2018 $ 15,588 2019 15,595 2020 325,688 2021 — 2022 — Beyond — Total $ 356,871

Leases

Leases	12 Months Ended
	Oct. 01, 2017
Leases [Abstract]
Leases	Leases We lease office and field equipment, vehicles and buildings under various operating leases. In fiscal 2017 , 2016 and 2015 , we recognized $71.3 million , $75.0 million and $66.4 million of expense associated with operating leases, respectively. The following are amounts payable under non-cancelable operating and capital lease commitments for the next five fiscal years and beyond: Operating Capital (in thousands) 2018 $ 77,854 $ 158 2019 62,634 211 2020 45,906 — 2021 28,740 — 2022 17,261 — Beyond 21,770 — Total $ 254,165 $ 369 Less: Amounts representing interest 2 Net present value $ 367 We vacated certain facilities under long-term non-cancelable leases and recorded contract termination costs of $2.9 million in fiscal 2016 . These amounts were initially measured at the fair value of the portion of the lease payments associated with the vacated facilities, reduced by estimated sublease rentals, less the write off of a prorated portion of existing deferred items previously recognized on these leases. We expect the remaining lease payments to be paid through the various lease expiration dates that continue until 2025. We initially measured the lease contract termination liability at the fair value of the prorated portion of the lease payments associated with the vacated facilities, reduced by estimated sublease rentals and other costs. If the actual timing and potential termination costs or realization of sublease income differ from our estimates, the resulting liabilities could vary from recorded amounts. These liabilities are reviewed periodically and adjusted when necessary. The following is a reconciliation of the beginning and ending balances of these liabilities related to lease contract termination costs: WEI RME RCM Total (in thousands) Balance at September 27, 2015 $ 531 $ 2,461 $ 177 $ 3,169 Cost transfer between groups 637 (637) — — Cost incurred and charged to expense 1,418 749 — 2,167 Adjustments (1) (1,034 ) (1,060) (138 ) (2,232 ) Balance at October 2, 2016 1,552 1,513 39 $ 3,104 Adjustments (1) (1,009 ) (365 ) (36 ) (1,410 ) Balance at October 1, 2017 $ 543 $ 1,148 $ 3 $ 1,694 (1) Adjustments of the actual timing and potential termination costs or realization of sublease income.

Stockholders' Equity and Stock

Stockholders' Equity and Stock Compensation Plans	12 Months Ended
	Oct. 01, 2017
Stockholders' Equity Note [Abstract]
Stockholders' Equity and Stock Compensation Plans	Stockholders' Equity and Stock Compensation Plans At October 1, 2017 , we had the following stock-based compensation plans: • Employee Stock Purchase Plan ("ESPP"). Purchase rights to purchase common stock are granted to our eligible full and part-time employees, and shares of common stock are issued upon exercise of the purchase rights. An aggregate of 2,373,290 shares may be issued pursuant to such exercise. The maximum amount that an employee can contribute during a purchase right period is $5,000 . The exercise price of a purchase right is the lesser of 100% of the fair market value of a share of common stock on the first day of the purchase right period or 85% of the fair market value on the last day of the purchase right period (December 15, or the business day preceding December 15 if December 15 is not a business day). • 2005 Equity Incentive Plan ("2005 EIP"). Key employees and non-employee directors may be granted equity awards, including stock options, restricted stock and restricted stock units ("RSUs"). Options granted before March 6, 2006 vested at 25% on the first anniversary of the grant date, and the balance vests monthly thereafter, such that these options become fully vested no later than four years from the date of grant. These options expire no later than ten years from the date of grant. Options granted on and after March 6, 2006 vest at 25% on each anniversary of the grant date. These options expire no later than eight years from the grant date. RSUs granted to date vest at 25% on each anniversary of the grant date. Our Compensation Committee has also awarded restricted stock to executive officers and non-employee directors under the 2005 EIP. Restricted stock grants generally vest over a minimum three -year period, and may be performance-based, determined by EPS growth, or service-based. No awards have made under the 2005 EIP since the adoption of the 2015 Equity Incentive Plan described below. • 2015 Equity Incentive Plan ("2015 EIP"). Key employees and non-employee directors may be granted equity awards, including stock options, performance share units ("PSUs") and RSUs. Shares issued with respect to awards granted under the 2015 EIP other than stock options or stock appreciation rights, which are referred to as "full value awards", are counted against the 2015 EIP's aggregate share limit as three shares for every share or unit actually issued. At October 1, 2017 , there were 2.6 million shares available for future awards pursuant to the 2015 EIP. The stock-based compensation and related income tax benefits were as follows: Fiscal Year Ended October 1, October 2, September 27, (in thousands) Total stock-based compensation $ 13,450 $ 12,964 $ 10,926 Income tax benefit related to stock-based compensation (4,715 ) (4,656 ) (3,811 ) Stock-based compensation, net of tax benefit $ 8,735 $ 8,308 $ 7,115 Stock Options Stock option activity for the fiscal year ended October 1, 2017 was as follows: Number of Options (in thousands) Weighted- Average Exercise Price per Share Weighted- Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding on October 2, 2016 2,367 $ 24.88 Granted 183 40.67 Exercised (791 ) 44.19 Forfeited (6 ) 17.72 Outstanding at October 1, 2017 1,753 27.18 4.59 $ 33,963 Vested or expected to vest at October 1, 2017 1,696 27.31 4.50 32,640 Exercisable on October 1, 2017 1,242 25.10 3.43 26,636 The aggregate intrinsic value in the table above represents the total intrinsic value (the difference between our closing stock price on the last trading day of fiscal 2017 and the exercise price, times the number of shares) that would have been received by the in-the-money option holders if they had exercised their options on October 1, 2017 . This amount will change based on the fair market value of our stock. At October 1, 2017 , we expect to recognize $3.5 million of unrecognized compensation cost related to stock option grants over a weighted-average period of 2 years . The weighted-average fair value of stock options granted during fiscal 2017 , 2016 and 2015 was $12.35 , $8.05 and $8.20 , respectively. The aggregate intrinsic value of options exercised during fiscal 2017 , 2016 and 2015 was $16.4 million , $7.3 million and $2.3 million , respectively. The fair value of our stock options was estimated on the date of grant using the Black-Scholes option pricing model. The following assumptions were used in the calculation: Fiscal Year Ended October 1, October 2, September 27, Dividend yield 1.0% 1.2% 1.0% Expected stock price volatility 36.1% - 38.8% 36.1% - 38.8% 36.2% - 38.8% Risk-free rate of return, annual 1.7% - 1.9% 1.6% - 1.8% 1.5% - 1.7% For purposes of the Black-Scholes model, forfeitures were estimated based on historical experience. For the fiscal 2017 , 2016 and 2015 year-ends, we based our expected stock price volatility on historical volatility behavior and current implied volatility behavior. Our risk-free rate of return was based on constant maturity rates provided by the U.S. Treasury. The expected life was based on historical experience. Net cash proceeds from the exercise of stock options were $18.6 million , $18.0 million and $10.8 million for fiscal 2017 , 2016 and 2015 , respectively. Our policy is to issue shares from our authorized shares upon the exercise of stock options. The actual income tax benefit realized from exercises of nonqualified stock options and disqualifying dispositions of qualified options for fiscal 2017 , 2016 and 2015 was $4.9 million , $5.3 million and $3.0 million , respectively. Restricted Stock, PSUs and RSUs The fair value of the total compensation cost of each restricted stock award was determined at the date of grant using the market price of the underlying common stock as of the date of grant. For performance-based awards, our expected performance is reviewed to estimate the percentage of shares that will vest. The total compensation cost of the awards is then amortized over their applicable vesting period on a straight-line basis. Restricted stock activity for the fiscal year ended October 1, 2017 was as follows: Number of Shares (in thousands) Weighted- Average Grant Date Fair Value Nonvested balance at October 2, 2016 35 $ 28.58 Granted 14 28.58 Vested (49 ) 28.58 Forfeited — — Nonvested balance at October 1, 2017 — — Vested or expected to vest at October 1, 2017 — — In fiscal 2017 , 2016 and 2015 , we did not award shares of restricted stock to our executive officers or non-employee directors. PSU activity for the fiscal year ended October 1, 2017 was as follows: Number of Shares (in thousands) Weighted- Average Grant Date Fair Value Nonvested balance at October 2, 2016 277 $ 31.65 Granted 99 48.36 Nonvested balance at October 1, 2017 376 36.05 In fiscal 2017 , we awarded 99,180 PSUs to our executive officers and non-employee directors at the weighted-average fair value of $48.36 per share on the award date. All of the PSUs are performance-based and vest, if at all, after the conclusion of the three -year performance period. The number of PSUs that ultimately vest is based 50% on the growth in our EPS and 50% on our relative total shareholder return over the vesting period. In fiscal 2016 , we awarded 137,777 PSUs to our executive officers and non-employee directors at the weighted-average fair value of $31.63 per share on the award date. All of the PSUs are performance-based and vest, if at all, after the conclusion of the three -year performance period. The number of PSUs that ultimately vest is based 50% on the growth in our EPS and 50% on our relative total shareholder return over the vesting period. RSU activity for the fiscal year ended October 1, 2017 was as follows: Number of Shares (in thousands) Weighted- Average Grant Date Fair Value Nonvested balance at October 2, 2016 499 $ 27.16 Granted 226 41.00 Vested (186 ) 26.98 Forfeited (28 ) 30.15 Nonvested balance at October 1, 2017 511 33.19 In fiscal 2017 , we also awarded 226,241 RSUs to our key employees and non-employee directors at a weighted average fair value of $41.00 per share on the award date. All of the RSUs have time-based vesting over a four -year period, except that RSUs awarded to directors vest after one year . At October 1, 2017 , there were 510,975 RSUs outstanding. RSU forfeitures result from employment terminations prior to vesting. Forfeited shares return to the pool of authorized shares available for award. In fiscal 2016 , we awarded 216,539 RSUs to our key employees and non-employee directors at the weighted average fair value of $27.14 per share on the award date. All of the RSUs have time-based vesting over a four -year period, except that RSUs awarded to directors vest after one year . At October 2, 2016 , there were 499,021 RSUs outstanding. RSU forfeitures result from employment terminations prior to vesting. Forfeited RSUs return to the pool of authorized shares available for award. The stock-based compensation expense related to restricted stock, PSUs and RSUs for fiscal years 2017 , 2016 and 2015 was $10.6 million , $10.3 million and $7.5 million , respectively, and was included in total stock-based compensation expense. At October 1, 2017 , there was $15.1 million of unrecognized compensation costs related to restricted stock, PSUs and RSUs that will be substantially recognized by the end of fiscal 2019. ESPP The following table summarizes shares purchased, weighted-average purchase price, cash received and the aggregate intrinsic value for shares purchased under the ESPP: Fiscal Year Ended October 1, October 2, September 27, (in thousands, except for purchase price) Shares purchased 190 209 243 Weighted-average purchase price $ 26.02 $ 22.54 $ 21.44 Cash received from exercise of purchase rights $ 4,940 $ 4,707 $ 5,204 Aggregate intrinsic value $ — $ 710 $ 1,277 The grant date fair value of each award granted under the ESPP was estimated using the Black-Scholes option pricing model with the following assumptions: Fiscal Year Ended October 1, October 2, September 27, Dividend yield 1.0% 1.3% 1.1% Expected stock price volatility 22.4% 23.7% 23.7% Risk-free rate of return, annual 0.9% 0.2% 0.2% Expected life (in years) 1 1 1 For fiscal 2017 , 2016 and 2015 , we based our expected stock price volatility on historical volatility behavior and current implied volatility behavior. The risk-free rate of return was based on constant maturity rates provided by the U.S. Treasury. The expected life was based on the ESPP terms and conditions. Included in stock-based compensation expense for fiscal 2017 , 2016 and 2015 was $0.5 million , $0.4 million and $0.6 million , respectively, related to the ESPP. The unrecognized stock-based compensation costs for awards granted under the ESPP at October 1, 2017 and October 2, 2016 were $0.1 million and $0.1 million , respectively. At October 1, 2017 , ESPP participants had accumulated $3.1 million to purchase our common stock.

Retirement Plans

Retirement Plans	12 Months Ended
	Oct. 01, 2017
Retirement Benefits [Abstract]
Retirement Plans	Retirement Plans We have established defined contribution plans including 401(k) plans. Generally, employees are eligible to participate in the defined contribution plans upon completion of one year of service and in the 401(k) plans upon commencement of employment. For fiscal 2017 , 2016 and 2015 , employer contributions to the plans were $11.4 million , $10.7 million and $9.8 million , respectively. We have established a non-qualified deferred compensation plan for certain key employees and non-employee directors. Eligible employees and non-employee directors may elect to defer the receipt of salary, incentive payments, restricted stock, PSU and RSU awards, and non-employee director fees, which are generally invested by us in individual variable life insurance contracts we own that are designed to informally fund savings plans of this nature. At October 1, 2017 and October 2, 2016 , the consolidated balance sheets reflect assets of $25.0 million and $20.9 million , respectively, related to the deferred compensation plan in "Other long-term assets," and liabilities of $25.2 million and $20.8 million , respectively, related to the deferred compensation plan in "Other long-term liabilities."

Earnings Per Share

Earnings Per Share	12 Months Ended
	Oct. 01, 2017
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share The following table sets forth the number of weighted-average shares used to compute basic and diluted EPS: Fiscal Year Ended October 1, October 2, September 27, (in thousands, except per share data) Net income attributable to Tetra Tech $ 117,874 $ 83,783 $ 39,074 Weighted-average common shares outstanding – basic 56,911 58,186 60,913 Effect of diluted stock options and unvested restricted stock 1,002 780 619 Weighted-average common stock outstanding – diluted 57,913 58,966 61,532 Earnings per share attributable to Tetra Tech: Basic $ 2.07 $ 1.44 $ 0.64 Diluted $ 2.04 $ 1.42 $ 0.64 For fiscal 2017 and 2016, no options were excluded from the calculation of dilutive potential common shares. For fiscal 2015 , 1.0 million options were excluded from the calculation of dilutive potential common shares. These options were not included in the computation of dilutive potential common shares because the assumed proceeds per share exceeded the average market price per share for that period. Therefore, their inclusion would have been anti-dilutive.

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Oct. 01, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments We use certain interest rate derivative contracts to hedge interest rate exposures on our variable rate debt. We enter into foreign currency derivative contracts with financial institutions to reduce the risk that cash flows and earnings will be adversely affected by foreign currency exchange rate fluctuations. Our hedging program is not designated for trading or speculative purposes. We recognize derivative instruments as either assets or liabilities on the accompanying consolidated balance sheets at fair value. We record changes in the fair value (i.e., gains or losses) of the derivatives that have been designated as cash flow hedges in our consolidated balance sheets as accumulated other comprehensive income (loss), and in our consolidated statements of income for those derivatives designated as fair value hedges. In fiscal 2013, we entered into three interest rate swap agreements that we have designated as cash flow hedges to fix the variable interest rates on a portion of borrowings under our term loan facility. In the first quarter of fiscal 2014, we entered into two interest rate swap agreements that we designated as cash flow hedges to fix the variable interest rates on the borrowings under our term loan facility. At October 1, 2017 and October 2, 2016 , the effective portion of our interest rate swap agreements designated as cash flow hedges before tax effect was $(0.05) million and $1.6 million , respectively, all of which we expect to be reclassified from accumulated other comprehensive income (loss) to interest expense within the next 12 months. As of October 1, 2017 , the notional principal, fixed rates and related expiration dates of our outstanding interest rate swap agreements are as follows: Notional Amount (in thousands) Fixed Rate Expiration Date $40,359 1.36% May 2018 40,359 1.34% May 2018 40,359 1.35% May 2018 20,180 1.23% May 2018 20,180 1.24% May 2018 The fair values of our outstanding derivatives designated as hedging instruments were as follows: Fair Value of Derivative Instruments as of Balance Sheet Location October 1, October 2, (in thousands) Interest rate swap agreements Other current assets (liabilities) $ 49 $ (1,572 ) The impact of the effective portions of derivative instruments in cash flow hedging relationships and fair value relationships on income and other comprehensive income was immaterial for the fiscal years ended October 1, 2017 and October 2, 2016 . Additionally, there were no ineffective portions of derivative instruments. Accordingly, no amounts were excluded from effectiveness testing for our interest rate swap agreements. We had no derivative instruments that were not designated as hedging instruments for fiscal 2017 , 2016 and 2015 .

Reclassifications Out of Accumu

Reclassifications Out of Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Oct. 01, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)	Reclassifications Out of Accumulated Other Comprehensive Income (Loss) The accumulated balances and reporting period activities for fiscal 2017 and 2016 related to reclassifications out of accumulated other comprehensive income (loss) are summarized as follows: Foreign Currency Translation Adjustments Gain (Loss) on Derivative Instruments Accumulated Other Comprehensive Income (Loss) (in thousands) Balances at September 27, 2015 $ (141,229 ) $ (1,942 ) $ (143,171 ) Other comprehensive income before reclassifications 14,389 2,718 17,107 Amounts reclassified from accumulated other comprehensive income Interest rate contracts, net of tax (1) — (1,944 ) (1,944 ) Net current-period other comprehensive income 14,389 774 15,163 Balances at October 2, 2016 $ (126,840 ) $ (1,168 ) $ (128,008 ) Other comprehensive income before reclassifications 27,894 2,363 30,257 Amounts reclassified from accumulated other comprehensive income Interest rate contracts, net of tax (1) — (749 ) (749 ) Net current-period other comprehensive income 27,894 1,614 29,508 Balances at October 1, 2017 $ (98,946 ) $ 446 $ (98,500 ) (1) This accumulated other comprehensive component is reclassified to "Interest expense" in our consolidated statements of income. See Note 14 , " Derivative Financial Instruments ", for more information.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Oct. 01, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Derivative Instruments. For additional information about our derivative financial instruments (see Note 2 , " Basis of Presentation and Preparation " and Note 14 , " Derivative Financial Instruments "). Contingent Consideration. We measure our contingent earn-out liabilities at fair value on a recurring basis (see Note 2 , " Basis of Presentation and Preparation " and Note 5 , " Mergers and Acquisitions " for further information). Debt. The fair value of long-term debt was determined using the present value of future cash flows based on the borrowing rates currently available for debt with similar terms and maturities (Level 2 measurement, as described in Note 2 , " Basis of Presentation and Preparation – Fair Value of Financial Instruments"). The carrying value of our long-term debt approximated fair value at October 1, 2017 and October 2, 2016 . At October 1, 2017 , we had borrowings of $356.4 million outstanding under our Credit Agreement, which were used to fund our business acquisitions, working capital needs, capital expenditures and contingent earn-outs (see Note 9 , " Long-Term Debt " for more information).

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Oct. 01, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies We are subject to certain claims and lawsuits typically filed against the engineering, consulting and construction profession, alleging primarily professional errors or omissions. We carry professional liability insurance, subject to certain deductibles and policy limits, against such claims. However, in some actions, parties are seeking damages that exceed our insurance coverage or for which we are not insured. While management does not believe that the resolution of these claims will have a material adverse effect, individually or in aggregate, on our financial position, results of operations or cash flows, management acknowledges the uncertainty surrounding the ultimate resolution of these matters.

Reportable Segments

Reportable Segments	12 Months Ended
	Oct. 01, 2017
Segment Reporting [Abstract]
Reportable Segments	Reportable Segments Our reportable segments are described as follows: WEI: WEI provides consulting and engineering services worldwide for a broad range of water and infrastructure-related needs in both developed and emerging economies. WEI supports both public and private clients including federal, state/provincial, and local governments, and global and local commercial clients. The primary markets for WEI’s services include water resources analysis and water management, environmental restoration, government consulting, and a broad range of civil infrastructure master planning and engineering design for facilities, transportation, and regional and local development. WEI’s services span from early data collection and monitoring, to data analysis and information technology, to science and engineering applied research, to engineering design, to construction management and operations and maintenance. RME: RME provides consulting and engineering services worldwide for a broad range of resource management and energy needs. RME supports both private and public clients, including global industrial and commercial clients, U.S. federal agencies in large scale remediation, and major international development agencies. The primary markets for RME’s services include natural resources, energy, international development, remediation, waste management and utilities. RME’s services span from early data collection and monitoring, to data analysis and information technology, to science and engineering applied research, to engineering design, to construction management and operations and maintenance. RME also supports engineering, procurement and construction management (“EPCM”) for full service implementation of commercial projects. RCM: We report the results of the wind-down of our non-core construction activities in the RCM reportable segment. The remaining work to be performed in this segment will be substantially completed in calendar 2017. Management evaluates the performance of these reportable segments based upon their respective segment operating income before the effect of amortization expense related to acquisitions, and other unallocated corporate expenses. We account for inter-segment sales and transfers as if the sales and transfers were to third parties; that is, by applying a negotiated fee onto the costs of the services performed. All significant intercompany balances and transactions are eliminated in consolidation. In fiscal 2016 , the Corporate segment operating losses included $19.5 million of acquisition and integration expenses, as described in Note 5 , " Mergers and Acquisitions ". The following tables set forth summarized financial information concerning our reportable segments: Reportable Segments Fiscal Year Ended October 1, October 2, September 27, (in thousands) Revenue WEI $ 1,146,366 $ 1,028,281 $ 993,631 RME 1,666,364 1,569,702 1,282,046 RCM 18,207 52,150 86,575 Elimination of inter-segment revenue (77,577 ) (66,664 ) (62,931 ) Total revenue $ 2,753,360 $ 2,583,469 $ 2,299,321 Operating Income (Loss) WEI $ 117,894 $ 95,996 $ 93,142 RME 111,122 112,202 93,359 RCM (14,712 ) (11,834 ) (8,614 ) Corporate (1) (30,962 ) (60,509 ) (90,203 ) Total operating income $ 183,342 $ 135,855 $ 87,684 Depreciation WEI $ 4,690 $ 4,797 $ 5,335 RME 15,142 15,703 13,342 RCM 1,062 736 1,801 Corporate 1,313 1,520 2,632 Total depreciation $ 22,207 $ 22,756 $ 23,110 (1) Includes goodwill and other intangible assets impairment charges, amortization of intangibles, other costs and other income not allocable to segments. The impairment charges of $60.8 million for fiscal 2015 was recorded at Corporate. The intangible asset amortization expense for fiscal 2017 , 2016 and 2015 was 22.8 million , $22.1 million and 20.2 million , respectively. Corporate results also included income (loss) for fair value adjustments to contingent consideration liabilities of 6.9 million , $(2.8) million and $3.1 million for fiscal 2017 , 2016 and 2015 , respectively. Fiscal 2016 also included 19.5 million of acquisition and integration related expenses recorded at Corporate. October 1, October 2, (in thousands) Total Assets WEI $ 354,709 $ 308,438 RME 555,485 522,895 RCM 33,620 39,107 Corporate (1) 958,931 930,339 Total assets $ 1,902,745 $ 1,800,779 (1) Corporate assets consist of intercompany eliminations and assets not allocated to segments including goodwill, intangible assets, deferred income taxes and certain other assets. Geographic Information Fiscal Year Ended October 1, 2017 October 2, 2016 September 27, 2015 Revenue Long-Lived Assets (2) Revenue Long-Lived Assets (2) Revenue Long-Lived Assets (2) United States $ 2,018,841 $ 58,965 $ 1,858,551 $ 59,334 $ 1,734,439 $ 61,526 Foreign countries (1) 734,519 34,183 724,918 39,067 564,882 32,230 (1) Includes revenue generated from our foreign operations, primarily in Canada and Australia, and revenue generated from non-U.S. clients. Long-lived assets consist primarily of amounts from our Canadian operations. (2) Excludes goodwill and other intangible assets. Major Clients Other than the U.S. federal government, we had no single client that accounted for more than 10% of our revenue. All of our segments generated revenue from all client sectors. The following table presents our revenue by client sector: Fiscal Year Ended October 1, October 2, September 27, (in thousands) Client Sector International (1) $ 734,519 $ 724,918 $ 564,882 U.S commercial 764,643 763,443 736,815 U.S. federal government (2) 901,136 784,368 709,600 U.S. state and local government 353,062 310,740 288,024 Total $ 2,753,360 $ 2,583,469 $ 2,299,321 (1) Includes revenue generated from foreign operations, primarily in Canada and Australia, and revenue generated from non-U.S. clients. (2) Includes revenue generated under U.S. federal government contracts performed outside the United States.

Quarterly Financial Information

Quarterly Financial Information-Unaudited	12 Months Ended
	Oct. 01, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information-Unaudited	Quarterly Financial Information – Unaudited In the opinion of management, the following unaudited quarterly data for the fiscal years ended October 1, 2017 and October 2, 2016 reflect all adjustments necessary for a fair statement of the results of operations. In fiscal 2016 , we incurred Coffey-related acquisition and integration expenses totaling $19.5 million . These costs were recognized in the second, third, and fourth quarters of fiscal 2016 in the amounts of $15.9 million , $1.0 million , and $2.6 million , respectively. In addition, interest expense in fiscal 2016 includes Coffey-related debt pre-payment fees of $1.9 million that were incurred in the second quarter. First Quarter Second Quarter Third Quarter Fourth Quarter (in thousands, except per share data) Fiscal Year 2017 Revenue $ 668,851 $ 663,781 $ 685,539 $ 735,188 Operating income 39,855 42,956 45,884 54,647 Net income attributable to Tetra Tech 26,562 26,862 29,983 34,467 Earnings per share attributable to Tetra Tech (1) : Basic $ 0.47 $ 0.47 $ 0.52 $ 0.61 Diluted $ 0.46 $ 0.46 $ 0.52 $ 0.60 Weighted-average common shares outstanding: Basic 57,099 57,270 57,184 56,338 Diluted 58,145 58,270 58,161 57,326 Fiscal Year 2016 Revenue $ 560,708 $ 627,384 $ 666,869 $ 728,508 Operating income 32,930 16,650 39,085 47,190 Net income attributable to Tetra Tech 23,239 3,744 25,694 31,106 Earnings per share attributable to Tetra Tech (1) : Basic $ 0.39 $ 0.06 $ 0.44 $ 0.54 Diluted $ 0.39 $ 0.06 $ 0.44 $ 0.53 Weighted-average common shares outstanding: Basic 59,058 58,451 57,796 57,309 Diluted 59,793 59,131 58,616 58,192 (1) The sum of the quarterly EPS may not add up to the full-year EPS due to rounding .

SCHEDULE II-VALUATION AND QUALI

SCHEDULE II-VALUATION AND QUALIFYING ACCOUNTS AND RESERVES	12 Months Ended
	Oct. 01, 2017
Valuation and Qualifying Accounts [Abstract]
SCHEDULE II-VALUATION AND QUALIFYING ACCOUNTS AND RESERVES	SCHEDULE II – VALUATION AND QUALIFYING ACCOUNTS AND RESERVES For the Fiscal Years Ended September 27, 2015 , October 2, 2016 and October 1, 2017 (in thousands) Balance at Beginning of Period Charged to Costs, Expenses and Revenue Deductions (1) Other (2) Balance at End of Period Allowance for doubtful accounts: Fiscal 2015 $ 39,780 $ (1,034 ) $ (5,965 ) (1,291 ) $ 31,490 Fiscal 2016 31,490 8,082 (12,191 ) 7,852 35,233 Fiscal 2017 35,233 2,848 (6,233 ) 411 32,259 Income tax valuation allowance: Fiscal 2015 $ 7,576 $ 4,609 $ — $ (4,394 ) $ 7,791 Fiscal 2016 7,791 3,856 — 13,800 25,447 Fiscal 2017 25,447 (121 ) — — 25,326 (1) Primarily represents uncollectible accounts written off, net of recoveries. (2) Includes allowances from new business acquisitions, loss in foreign jurisdictions, currency adjustments, and valuation allowance adjustments related to net operating loss carry-forwards .

Basis of Presentation and Pre30

Basis of Presentation and Preparation (Policies)	12 Months Ended
	Oct. 01, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Principles of Consolidation and Presentation	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	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	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	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. 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	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	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. 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	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	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 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	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	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	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	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	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	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.
Foreign Currency Translation	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	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

Accounts Receivable - Net and31

Accounts Receivable - Net and Revenue Recognition (Tables)	12 Months Ended
	Oct. 01, 2017
Accounts Receivable - Net and Revenue Recognition
Net accounts receivable and billings in excess of costs on uncompleted contracts	Net accounts receivable and billings in excess of costs on uncompleted contracts consisted of the following at October 1, 2017 and October 2, 2016 : October 1, October 2, (in thousands) Billed $ 376,287 $ 364,287 Unbilled 404,899 356,147 Contract retentions 39,840 29,135 Total accounts receivable – gross 821,026 749,569 Allowance for doubtful accounts (32,259 ) (35,233 ) Total accounts receivable – net $ 788,767 $ 714,336 Billings in excess of costs on uncompleted contracts $ 117,499 $ 88,223

Mergers and Acquisitions (Table

Mergers and Acquisitions (Tables)	12 Months Ended
	Oct. 01, 2017
Business Combinations [Abstract]
Summary of estimated fair values of assets acquired and liabilities assumed	The following table summarizes the estimated fair values of assets acquired and liabilities assumed as of the respective acquisition dates for our acquisitions completed in fiscal 2016 (in thousands): Accounts receivable $ 71,515 Other current assets 18,869 Property and equipment 14,218 Goodwill 108,323 Backlog and trade name intangible assets 29,445 Other assets 747 Current liabilities (78,311 ) Borrowings (65,086 ) Other long-term liabilities (4,885 ) Net assets acquired $ 94,835
Summary of consolidated pro forma operating results	The table below presents summarized unaudited consolidated pro forma operating results including the related acquisition, integration and debt pre-payment charges, assuming we had acquired Coffey and INDUS at the beginning of fiscal 2016 . These pro-forma operating results are presented for illustrative purposes only and are not indicative of the operating results that would have been achieved had the related events occurred at the beginning of fiscal 2016 . Pro-Forma Fiscal Year Ended October 1, October 2, (in thousands, except per share data) Revenue $ 2,753,360 $ 2,714,658 Operating income 183,342 152,676 Net income attributable to Tetra Tech 117,874 98,871 Earnings per share attributable to Tetra Tech Basic $ 2.07 $ 1.70 Diluted $ 2.04 $ 1.68
Summary of acquisition and integration expenses	Acquisition and integration expenses in the accompanying consolidated statements of income are comprised of the following: Fiscal Year Ended (in thousands) Severance including change in control payments $ 10,917 Professional services 5,685 Real estate-related 2,946 Total $ 19,548
Summary of changes in the carrying value of estimated contingent earn-out liabilities	The following table summarizes the changes in the carrying value of estimated contingent earn-out liabilities: Fiscal Year Ended October 1, October 2, September 27, (in thousands) Beginning balance (at fair value) $ 8,757 $ 4,169 $ 7,030 Estimated earn-out liabilities for acquisitions during the fiscal year 1,604 4,745 4,100 Increases due to re-measurement of fair value reported in interest expense 260 271 136 Net increase (decrease) due to re-measurement of fair value reported as losses (gains) in operating income (6,923 ) 2,823 (3,113 ) Foreign exchange impact 59 — (785 ) Earn-out payments: Reported as cash used in operating activities — — — Reported as cash used in financing activities (1,319 ) (3,251 ) (3,199 ) Ending balance (at fair value) $ 2,438 $ 8,757 $ 4,169

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Oct. 01, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of carrying value of goodwill	The following table summarizes the changes in the carrying value of goodwill: WEI RME Total (in thousands) Balance at September 27, 2015 $ 210,748 $ 390,631 $ 601,379 Goodwill additions 9,080 98,538 107,618 Goodwill adjustments — 1,687 1,687 Foreign exchange translation 2,125 5,179 7,304 Balance at October 2, 2016 221,953 496,035 717,988 Goodwill additions — 7,055 7,055 Goodwill adjustments 13,509 (12,804 ) 705 Foreign exchange translation 6,273 8,865 15,138 Balance at October 1, 2017 $ 241,735 $ 499,151 $ 740,886
Summary of acquired identifiable intangible assets with finite useful lives	The gross amount and accumulated amortization of our acquired identifiable intangible assets with finite useful lives included in "Intangible assets – net" on the consolidated balance sheets, were as follows: Fiscal Year Ended October 1, 2017 October 2, 2016 Weighted- Average Remaining Life (in years) Gross Amount Accumulated Amortization Gross Amount Accumulated Amortization ($ in thousands) Non-compete agreements 0.1 $ 495 $ (493 ) $ 881 $ (840 ) Client relations 2.9 90,297 (75,074 ) 112,367 (83,514 ) Backlog 1.4 21,518 (13,301 ) 23,018 (7,536 ) Technology and trade names 3.3 6,685 (3,439 ) 7,778 (3,192 ) Total $ 118,995 $ (92,307 ) $ 144,044 $ (95,082 )
Estimated amortization expense for the succeeding five years and beyond	Estimated amortization expense for the succeeding five years and beyond is as follows: Amount (in thousands) 2018 $ 14,548 2019 7,034 2020 2,802 2021 1,664 2022 411 Beyond 229 Total $ 26,688

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Oct. 01, 2017
Property, Plant and Equipment [Abstract]
Schedule of components of property and equipment	Property and equipment consisted of the following: Fiscal Year Ended October 1, October 2, (in thousands) Land and buildings $ 3,680 $ 3,683 Equipment, furniture and fixtures 150,026 180,750 Leasehold improvements 27,689 30,261 Total property and equipment 181,395 214,694 Accumulated depreciation (124,560 ) (146,867 ) Property and equipment, net $ 56,835 $ 67,827

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Oct. 01, 2017
Income Tax Disclosure [Abstract]
Schedule of income before income taxes, by geographical area	The income before income taxes, by geographic area, was as follows: Fiscal Year Ended October 1, October 2, September 27, (in thousands) Income before income taxes: United States $ 166,074 $ 113,576 $ 118,822 Foreign 5,687 10,890 (38,501 ) Total income before income taxes $ 171,761 $ 124,466 $ 80,321
Schedule of components of income tax expense	Income tax expense consisted of the following: Fiscal Year Ended October 1, October 2, September 27, (in thousands) Current: Federal $ 45,604 $ 22,277 $ 23,836 State 8,860 5,634 5,072 Foreign 9,337 6,651 3,773 Total current income tax expense 63,801 34,562 32,681 Deferred: Federal (4,251 ) 6,231 7,218 State (945 ) (16 ) 2,335 Foreign (4,761 ) (164 ) (1,141 ) Total deferred income tax expense (9,957 ) 6,051 8,412 Total income tax expense $ 53,844 $ 40,613 $ 41,093
Schedule of reconciliation of income tax expense and effective income tax rates	Total income tax expense was different from the amount computed by applying the U.S. federal statutory rate to pre-tax income as follows: Fiscal Year Ended October 1, October 2, September 27, Tax at federal statutory rate 35.0% 35.0% 35.0% State taxes, net of federal benefit 3.4 3.1 5.0 Research and Development ("R&D") credit (1.8) (3.4) (3.8) Domestic production deduction (0.7) (0.7) (0.8) Tax differential on foreign earnings — (1.6) (3.8) Non-taxable foreign interest income (2.9) (3.9) (5.9) Non-deductible executive compensation — 2.0 — Goodwill and contingent consideration — — 19.2 Stock compensation (2.8) 0.3 0.5 Valuation allowance (0.5) 2.4 5.7 Change in uncertain tax positions 1.8 (2.0) — Other (0.2) 1.4 0.1 Total income tax expense 31.3% 32.6% 51.2%
Schedule of temporary differences comprising the net deferred income tax liability	Temporary differences comprising the net deferred income tax liability shown on the accompanying consolidated balance sheets were as follows: Fiscal Year Ended October 1, October 2, (in thousands) Deferred Tax Assets: State taxes $ 598 $ 697 Reserves and contingent liabilities 2,941 2,539 Allowance for doubtful accounts 4,273 3,817 Accrued liabilities 22,466 24,663 Stock-based compensation 10,069 10,684 Intangibles — — Loss carry-forwards 28,261 23,514 Valuation allowance (25,326 ) (25,447 ) Total deferred tax assets 43,282 40,467 Deferred Tax Liabilities: Unbilled revenue (46,408 ) (54,638 ) Prepaid expense (6,253 ) (2,921 ) Intangibles (24,328 ) (33,268 ) Property and equipment (8,311 ) (9,358 ) Total deferred tax liability (85,300 ) (100,185 ) Net deferred tax liabilities $ (42,018 ) $ (59,718 )
Reconciliation of the beginning and ending amounts of unrecognized tax benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: Fiscal Year Ended October 1, October 2, September 27, (in thousands) Beginning balance $ 22,786 $ 21,618 $ 21,717 Additions for current year tax positions 1,060 2,802 1,147 Additions for prior year tax positions 2,365 1,466 2,309 Reductions for prior year tax positions (6,875 ) (3,100 ) (23 ) Settlements (9,999 ) — (3,532 ) Ending balance $ 9,337 $ 22,786 $ 21,618

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Oct. 01, 2017
Debt Disclosure [Abstract]
Schedule of long-term debt	Long-term debt consisted of the following: Fiscal Year Ended October 1, October 2, (in thousands) Credit facilities $ 356,438 $ 346,813 Other 433 198 Total long-term debt 356,871 347,011 Less: Current portion of long-term debt (15,588 ) (15,510 ) Long-term debt, less current portion $ 341,283 $ 331,501
Schedule of maturities of long-term debt	The following table presents scheduled maturities of our long-term debt: Amount (in thousands) 2018 $ 15,588 2019 15,595 2020 325,688 2021 — 2022 — Beyond — Total $ 356,871

Leases (Tables)

Leases (Tables)	12 Months Ended
	Oct. 01, 2017
Leases [Abstract]
Schedule of amounts payable under non-cancelable operating and capital lease commitments	The following are amounts payable under non-cancelable operating and capital lease commitments for the next five fiscal years and beyond: Operating Capital (in thousands) 2018 $ 77,854 $ 158 2019 62,634 211 2020 45,906 — 2021 28,740 — 2022 17,261 — Beyond 21,770 — Total $ 254,165 $ 369 Less: Amounts representing interest 2 Net present value $ 367
Schedule of reconciliation of the beginning and ending balances of liabilities related to lease contract termination costs	The following is a reconciliation of the beginning and ending balances of these liabilities related to lease contract termination costs: WEI RME RCM Total (in thousands) Balance at September 27, 2015 $ 531 $ 2,461 $ 177 $ 3,169 Cost transfer between groups 637 (637) — — Cost incurred and charged to expense 1,418 749 — 2,167 Adjustments (1) (1,034 ) (1,060) (138 ) (2,232 ) Balance at October 2, 2016 1,552 1,513 39 $ 3,104 Adjustments (1) (1,009 ) (365 ) (36 ) (1,410 ) Balance at October 1, 2017 $ 543 $ 1,148 $ 3 $ 1,694 (1) Adjustments of the actual timing and potential termination costs or realization of sublease income.

Stockholders' Equity and Stoc38

Stockholders' Equity and Stock Compensation Plans (Tables)	12 Months Ended
	Oct. 01, 2017
Stockholders' Equity Note [Abstract]
Schedule of the stock-based compensation and related income tax benefits	The stock-based compensation and related income tax benefits were as follows: Fiscal Year Ended October 1, October 2, September 27, (in thousands) Total stock-based compensation $ 13,450 $ 12,964 $ 10,926 Income tax benefit related to stock-based compensation (4,715 ) (4,656 ) (3,811 ) Stock-based compensation, net of tax benefit $ 8,735 $ 8,308 $ 7,115
Schedule of stock option activity	Stock option activity for the fiscal year ended October 1, 2017 was as follows: Number of Options (in thousands) Weighted- Average Exercise Price per Share Weighted- Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding on October 2, 2016 2,367 $ 24.88 Granted 183 40.67 Exercised (791 ) 44.19 Forfeited (6 ) 17.72 Outstanding at October 1, 2017 1,753 27.18 4.59 $ 33,963 Vested or expected to vest at October 1, 2017 1,696 27.31 4.50 32,640 Exercisable on October 1, 2017 1,242 25.10 3.43 26,636
Schedule of assumptions used in the calculation of the fair value of stock options using the Black-Scholes option pricing model	The fair value of our stock options was estimated on the date of grant using the Black-Scholes option pricing model. The following assumptions were used in the calculation: Fiscal Year Ended October 1, October 2, September 27, Dividend yield 1.0% 1.2% 1.0% Expected stock price volatility 36.1% - 38.8% 36.1% - 38.8% 36.2% - 38.8% Risk-free rate of return, annual 1.7% - 1.9% 1.6% - 1.8% 1.5% - 1.7%
Schedule of restricted stock activity	Restricted stock activity for the fiscal year ended October 1, 2017 was as follows: Number of Shares (in thousands) Weighted- Average Grant Date Fair Value Nonvested balance at October 2, 2016 35 $ 28.58 Granted 14 28.58 Vested (49 ) 28.58 Forfeited — — Nonvested balance at October 1, 2017 — — Vested or expected to vest at October 1, 2017 — —
Schedule of performance-based awards	PSU activity for the fiscal year ended October 1, 2017 was as follows: Number of Shares (in thousands) Weighted- Average Grant Date Fair Value Nonvested balance at October 2, 2016 277 $ 31.65 Granted 99 48.36 Nonvested balance at October 1, 2017 376 36.05
Schedule of RSU activity	RSU activity for the fiscal year ended October 1, 2017 was as follows: Number of Shares (in thousands) Weighted- Average Grant Date Fair Value Nonvested balance at October 2, 2016 499 $ 27.16 Granted 226 41.00 Vested (186 ) 26.98 Forfeited (28 ) 30.15 Nonvested balance at October 1, 2017 511 33.19
Summary of shares purchased, weighted-average purchase price, cash received, and the aggregate intrinsic value for shares purchased under the ESPP	The following table summarizes shares purchased, weighted-average purchase price, cash received and the aggregate intrinsic value for shares purchased under the ESPP: Fiscal Year Ended October 1, October 2, September 27, (in thousands, except for purchase price) Shares purchased 190 209 243 Weighted-average purchase price $ 26.02 $ 22.54 $ 21.44 Cash received from exercise of purchase rights $ 4,940 $ 4,707 $ 5,204 Aggregate intrinsic value $ — $ 710 $ 1,277
Schedule of the assumptions used in the Black-Scholes option pricing model in estimating the grant date fair value of each award granted under the ESPP	The grant date fair value of each award granted under the ESPP was estimated using the Black-Scholes option pricing model with the following assumptions: Fiscal Year Ended October 1, October 2, September 27, Dividend yield 1.0% 1.3% 1.1% Expected stock price volatility 22.4% 23.7% 23.7% Risk-free rate of return, annual 0.9% 0.2% 0.2% Expected life (in years) 1 1 1

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Oct. 01, 2017
Earnings Per Share [Abstract]
Schedule of number of weighted-average shares used to compute basic and diluted EPS	The following table sets forth the number of weighted-average shares used to compute basic and diluted EPS: Fiscal Year Ended October 1, October 2, September 27, (in thousands, except per share data) Net income attributable to Tetra Tech $ 117,874 $ 83,783 $ 39,074 Weighted-average common shares outstanding – basic 56,911 58,186 60,913 Effect of diluted stock options and unvested restricted stock 1,002 780 619 Weighted-average common stock outstanding – diluted 57,913 58,966 61,532 Earnings per share attributable to Tetra Tech: Basic $ 2.07 $ 1.44 $ 0.64 Diluted $ 2.04 $ 1.42 $ 0.64

Derivative Financial Instrume40

Derivative Financial Instruments (Tables)	12 Months Ended
	Oct. 01, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of notional principal, fixed rates and related expiration dates of outstanding interest rate swap agreements	As of October 1, 2017 , the notional principal, fixed rates and related expiration dates of our outstanding interest rate swap agreements are as follows: Notional Amount (in thousands) Fixed Rate Expiration Date $40,359 1.36% May 2018 40,359 1.34% May 2018 40,359 1.35% May 2018 20,180 1.23% May 2018 20,180 1.24% May 2018
Schedule of fair values of the entity's outstanding derivatives designated as hedging instruments	The fair values of our outstanding derivatives designated as hedging instruments were as follows: Fair Value of Derivative Instruments as of Balance Sheet Location October 1, October 2, (in thousands) Interest rate swap agreements Other current assets (liabilities) $ 49 $ (1,572 )

Reclassifications Out of Accu41

Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Oct. 01, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Summary of reclassifications out of accumulated other comprehensive income (loss)	The accumulated balances and reporting period activities for fiscal 2017 and 2016 related to reclassifications out of accumulated other comprehensive income (loss) are summarized as follows: Foreign Currency Translation Adjustments Gain (Loss) on Derivative Instruments Accumulated Other Comprehensive Income (Loss) (in thousands) Balances at September 27, 2015 $ (141,229 ) $ (1,942 ) $ (143,171 ) Other comprehensive income before reclassifications 14,389 2,718 17,107 Amounts reclassified from accumulated other comprehensive income Interest rate contracts, net of tax (1) — (1,944 ) (1,944 ) Net current-period other comprehensive income 14,389 774 15,163 Balances at October 2, 2016 $ (126,840 ) $ (1,168 ) $ (128,008 ) Other comprehensive income before reclassifications 27,894 2,363 30,257 Amounts reclassified from accumulated other comprehensive income Interest rate contracts, net of tax (1) — (749 ) (749 ) Net current-period other comprehensive income 27,894 1,614 29,508 Balances at October 1, 2017 $ (98,946 ) $ 446 $ (98,500 ) (1) This accumulated other comprehensive component is reclassified to "Interest expense" in our consolidated statements of income. See Note 14 , " Derivative Financial Instruments ", for more information.

Reportable Segments (Tables)

Reportable Segments (Tables)	12 Months Ended
	Oct. 01, 2017
Segment Reporting [Abstract]
Summarized financial information of reportable segments	The following tables set forth summarized financial information concerning our reportable segments: Reportable Segments Fiscal Year Ended October 1, October 2, September 27, (in thousands) Revenue WEI $ 1,146,366 $ 1,028,281 $ 993,631 RME 1,666,364 1,569,702 1,282,046 RCM 18,207 52,150 86,575 Elimination of inter-segment revenue (77,577 ) (66,664 ) (62,931 ) Total revenue $ 2,753,360 $ 2,583,469 $ 2,299,321 Operating Income (Loss) WEI $ 117,894 $ 95,996 $ 93,142 RME 111,122 112,202 93,359 RCM (14,712 ) (11,834 ) (8,614 ) Corporate (1) (30,962 ) (60,509 ) (90,203 ) Total operating income $ 183,342 $ 135,855 $ 87,684 Depreciation WEI $ 4,690 $ 4,797 $ 5,335 RME 15,142 15,703 13,342 RCM 1,062 736 1,801 Corporate 1,313 1,520 2,632 Total depreciation $ 22,207 $ 22,756 $ 23,110 (1) Includes goodwill and other intangible assets impairment charges, amortization of intangibles, other costs and other income not allocable to segments. The impairment charges of $60.8 million for fiscal 2015 was recorded at Corporate. The intangible asset amortization expense for fiscal 2017 , 2016 and 2015 was 22.8 million , $22.1 million and 20.2 million , respectively. Corporate results also included income (loss) for fair value adjustments to contingent consideration liabilities of 6.9 million , $(2.8) million and $3.1 million for fiscal 2017 , 2016 and 2015 , respectively. Fiscal 2016 also included 19.5 million of acquisition and integration related expenses recorded at Corporate. October 1, October 2, (in thousands) Total Assets WEI $ 354,709 $ 308,438 RME 555,485 522,895 RCM 33,620 39,107 Corporate (1) 958,931 930,339 Total assets $ 1,902,745 $ 1,800,779 (1) Corporate assets consist of intercompany eliminations and assets not allocated to segments including goodwill, intangible assets, deferred income taxes and certain other assets.
Schedule of geographic information	Geographic Information Fiscal Year Ended October 1, 2017 October 2, 2016 September 27, 2015 Revenue Long-Lived Assets (2) Revenue Long-Lived Assets (2) Revenue Long-Lived Assets (2) United States $ 2,018,841 $ 58,965 $ 1,858,551 $ 59,334 $ 1,734,439 $ 61,526 Foreign countries (1) 734,519 34,183 724,918 39,067 564,882 32,230 (1) Includes revenue generated from our foreign operations, primarily in Canada and Australia, and revenue generated from non-U.S. clients. Long-lived assets consist primarily of amounts from our Canadian operations. (2) Excludes goodwill and other intangible assets.
Summary of revenue by client sector	The following table presents our revenue by client sector: Fiscal Year Ended October 1, October 2, September 27, (in thousands) Client Sector International (1) $ 734,519 $ 724,918 $ 564,882 U.S commercial 764,643 763,443 736,815 U.S. federal government (2) 901,136 784,368 709,600 U.S. state and local government 353,062 310,740 288,024 Total $ 2,753,360 $ 2,583,469 $ 2,299,321 (1) Includes revenue generated from foreign operations, primarily in Canada and Australia, and revenue generated from non-U.S. clients. (2) Includes revenue generated under U.S. federal government contracts performed outside the United States.

Quarterly Financial Informati43

Quarterly Financial Information-Unaudited (Tables)	12 Months Ended
	Oct. 01, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of unaudited quarterly data	First Quarter Second Quarter Third Quarter Fourth Quarter (in thousands, except per share data) Fiscal Year 2017 Revenue $ 668,851 $ 663,781 $ 685,539 $ 735,188 Operating income 39,855 42,956 45,884 54,647 Net income attributable to Tetra Tech 26,562 26,862 29,983 34,467 Earnings per share attributable to Tetra Tech (1) : Basic $ 0.47 $ 0.47 $ 0.52 $ 0.61 Diluted $ 0.46 $ 0.46 $ 0.52 $ 0.60 Weighted-average common shares outstanding: Basic 57,099 57,270 57,184 56,338 Diluted 58,145 58,270 58,161 57,326 Fiscal Year 2016 Revenue $ 560,708 $ 627,384 $ 666,869 $ 728,508 Operating income 32,930 16,650 39,085 47,190 Net income attributable to Tetra Tech 23,239 3,744 25,694 31,106 Earnings per share attributable to Tetra Tech (1) : Basic $ 0.39 $ 0.06 $ 0.44 $ 0.54 Diluted $ 0.39 $ 0.06 $ 0.44 $ 0.53 Weighted-average common shares outstanding: Basic 59,058 58,451 57,796 57,309 Diluted 59,793 59,131 58,616 58,192 (1) The sum of the quarterly EPS may not add up to the full-year EPS due to rounding .

Description of Business (Detail

Description of Business (Details)	12 Months Ended
	Oct. 01, 2017segment
Description of Business
Number of reportable segments	3

Basis of Presentation and Pre45

Basis of Presentation and Preparation - Fiscal Year (Details)	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Principles of Consolidation and Presentation
Number of weeks in a fiscal year, low end of range	364 days
Number of weeks in a fiscal year, high end of range	371 days
Number of weeks in a fiscal year	364 days	371 days	364 days

Basis of Presentation and Pre46

Basis of Presentation and Preparation - Revenue Recognition and Contract Costs (Details)	12 Months Ended
	Oct. 01, 2017Contract
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of types of contracts under which revenue is recognized	3

Basis of Presentation and Pre47

Basis of Presentation and Preparation - Cash and Cash Equivalents and Accounts Receivable (Details) $ in Millions	12 Months Ended
	Oct. 01, 2017USD ($)
Cash and Cash Equivalents
Maximum term of original maturity to classify instrument as cash equivalent	90 days
Restricted cash included in "Prepaid expenses and other current assets"	$ 2.7
Accounts Receivable - Net
Period for billing and collecting unbilled receivables	12 months
Period for earning majority of billings in excess of costs	12 months

Basis of Presentation and Pre48

Basis of Presentation and Preparation - Property and Equipment (Details)	12 Months Ended
	Oct. 01, 2017
Equipment | Maximum
Estimated useful lives
Estimated useful lives	10 years
Equipment | Minimum
Estimated useful lives
Estimated useful lives	3 years
Furniture and fixtures | Maximum
Estimated useful lives
Estimated useful lives	10 years
Furniture and fixtures | Minimum
Estimated useful lives
Estimated useful lives	3 years
Buildings | Maximum
Estimated useful lives
Estimated useful lives	40 years

Basis of Presentation and Pre49

Basis of Presentation and Preparation - Goodwill and Intangible Assets (Details)	12 Months Ended
	Oct. 01, 2017LevelStep
Goodwill and Intangible Assets
Number of levels below reportable segments at which goodwill impairment testing is performed | Level	1
Number of steps involved in process of goodwill annual impairment test | Step	2

Basis of Presentation and Pre50

Basis of Presentation and Preparation - Contingent Consideration and Concentration of Credit Risk (Details)	12 Months Ended
	Oct. 01, 2017Institution
Concentration of Credit Risk
Financial institutions, in any such number of which investment exposure is limited	1
Accounts receivable due from various agencies of the U.S. federal government (as a percent)	23.00%
U.S. government
Concentration of Credit Risk
Revenue from customers (as a percent)	45.00%
U.S. commercial
Concentration of Credit Risk
Revenue from customers (as a percent)	28.00%
International
Concentration of Credit Risk
Revenue from customers (as a percent)	27.00%
Minimum
Contingent Consideration
Period for contingent earn-out payments	2 years
Maximum
Contingent Consideration
Period for contingent earn-out payments	3 years

Basis of Presentation and Pre51

Basis of Presentation and Preparation - Recently Adopted and Pending Accounting Guidance (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess tax benefits included in cash flows from operating activities	$ 137,992	$ 142,020	$ 162,847
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess tax benefit	4,900
Excess tax benefits included in cash flows from operating activities	$ 4,900

Stock Repurchase and Dividends

Stock Repurchase and Dividends (Details) - USD ($)	Nov. 06, 2017	Jul. 31, 2017	May 01, 2017	Jan. 30, 2017	Nov. 07, 2016	Oct. 01, 2017	Oct. 02, 2016
Subsequent Event [Line Items]
Maximum repurchase amount under stock repurchase program					$ 200,000,000
Shares repurchased through open market purchases						2,266,397
Average price of shares repurchased (in dollars per share)						$ 44.12
Cost of shares repurchased						$ 100,000,000
Quarterly cash dividend declared (in dollars per share)		$ 0.10	$ 0.10	$ 0.09	$ 0.09
Payment of dividends						$ 21,700,000	$ 19,700,000
Subsequent Event
Subsequent Event [Line Items]
Quarterly cash dividend declared (in dollars per share)	$ 0.10

Accounts Receivable - Net Accou

Accounts Receivable - Net Accounts Receivable and Billings in Excess of Costs on Uncompleted Contracts (Details) - USD ($) $ in Thousands	Oct. 01, 2017	Oct. 02, 2016
Accounts Receivable - Net and Revenue Recognition
Billed	$ 376,287	$ 364,287
Unbilled	404,899	356,147
Contract retentions	39,840	29,135
Total accounts receivable – gross	821,026	749,569
Allowance for doubtful accounts	(32,259)	(35,233)
Total accounts receivable – net	788,767	714,336
Billings in excess of costs on uncompleted contracts	$ 117,499	$ 88,223

Accounts Receivable - Net and54

Accounts Receivable - Net and Revenue Recognition (Details) - USD ($) $ in Millions	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Financial information concerning reportable segments
Period for billing and collecting unbilled receivables	12 months
Period for earning majority of billings in excess of costs	12 months
Unbilled accounts receivable related to claims and requests for equitable adjustment on contracts	$ 59	$ 45
Billed accounts receivable related to U.S. federal government contracts	45.4	47.4
U.S. federal government unbilled receivables	$ 109.7	$ 92.2
Threshold percentage for disclosure of accounts receivable from a single client	10.00%	10.00%
Net unfavorable operating income adjustments	$ 8		$ 8.9
Liability for anticipated losses	8.1	$ 6.7
Estimated cost to complete the related contracts	5
RCM
Financial information concerning reportable segments
Reduction in the revenue related to the evaluation of the claims	4.9
Gain (loss) from claim settlement	(3.6)	4.6
Cash proceeds from claim settlement		13.4
Claims settlement amount		8.8
Decrease in operating income related to the increase in allowance for doubtful accounts		7.9
Increase in allowance for doubtful accounts		7.9
Collectability of certain accounts receivable		4.6
Net unfavorable operating income adjustments	5.7	$ 2.3
RME
Financial information concerning reportable segments
Net unfavorable operating income adjustments	$ 2.3

Mergers and Acquisitions - Acqu

Mergers and Acquisitions - Acquisition Narrative (Details)	Oct. 02, 2017employee	Apr. 02, 2017USD ($)employee	Mar. 27, 2016USD ($)employee	Jun. 28, 2015USD ($)	Sep. 27, 2015USD ($)	Oct. 01, 2017USD ($)	Oct. 02, 2016USD ($)
Business acquisition
Contingent earn-out liability					$ 0	$ 2,400,000
Aggregate maximum of contingent consideration						$ 8,900,000
CEG
Business acquisition
Aggregate fair value of purchase prices					15,900,000
Cash paid to the sellers					11,800,000
Contingent earn-out liability		$ 1,800,000		$ 4,100,000	4,100,000		$ 3,900,000
Aggregate maximum of contingent consideration				$ 9,800,000	$ 9,800,000
Earn-out period				3 years
Coffey
Business acquisition
Aggregate fair value of purchase prices			$ 76,100,000
Number of employees | employee			3,300
Assumed debt			$ 65,100,000
Secured bank debt assumed			37,100,000
Unsecured corporate bonds assumed			28,000,000
INDUS
Business acquisition
Aggregate fair value of purchase prices			18,700,000
Cash paid to the sellers			14,000,000
Contingent earn-out liability		0	4,700,000				$ 4,900,000
Aggregate maximum of contingent consideration			$ 8,000,000
Earn-out period			2 years
ELA
Business acquisition
Aggregate fair value of purchase prices		9,900,000
Cash paid to the sellers		8,300,000
Contingent earn-out liability		1,600,000
Aggregate maximum of contingent consideration		$ 1,700,000
Number of employees | employee		160
Earn-out period		2 years
Glumac | Subsequent Event
Business acquisition
Number of employees | employee	300

Mergers and Acquisitions - Esti

Mergers and Acquisitions - Estimated Fair Value of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Business acquisition
Goodwill	$ 740,886	$ 717,988	$ 601,379
Minimum | Existing customer contracts
Business acquisition
Useful life of intangible assets	1 year
Minimum | Trade names
Business acquisition
Useful life of intangible assets	3 years
Maximum | Existing customer contracts
Business acquisition
Useful life of intangible assets	5 years
Maximum | Trade names
Business acquisition
Useful life of intangible assets	5 years
Weighted average | Existing customer contracts
Business acquisition
Useful life of intangible assets	3 years
Coffey and INDUS
Business acquisition
Accounts receivable		71,515
Other current assets		18,869
Property and equipment		14,218
Goodwill		108,323
Backlog and trade name intangible assets		29,445
Other assets		747
Current liabilities		(78,311)
Borrowings		(65,086)
Other long-term liabilities		(4,885)
Net assets acquired		$ 94,835

Mergers and Acquisitions - Pro-

Mergers and Acquisitions - Pro-Forma Operating Results (Details) - Coffey and INDUS - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016
Pro forma operating results
Revenue	$ 2,753,360	$ 2,714,658
Operating income	183,342	152,676
Net income attributable to Tetra Tech	$ 117,874	$ 98,871
Earnings per share attributable to Tetra Tech
Basic (in dollars per share)	$ 2.07	$ 1.7
Diluted (in dollars per share)	$ 2.04	$ 1.68

Mergers and Acquisitions - Comp

Mergers and Acquisitions - Components of Acquisition and Integration Expenses (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Oct. 02, 2016	Jun. 26, 2016	Mar. 27, 2016	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Business acquisition
Severance including change in control payments					$ 10,917
Professional services					5,685
Real estate-related					2,946
Total				$ 0	19,548	$ 0
Coffey
Business acquisition
Total	$ 2,600	$ 1,000	$ 15,900		19,500
Coffey | Interest expense
Business acquisition
Pre-payment charges paid			$ 1,900		$ 1,900

Mergers and Acquisitions - Cont

Mergers and Acquisitions - Contingent Consideration Narrative (Details) CAD in Millions	Jul. 03, 2017USD ($)	Oct. 01, 2017USD ($)	Apr. 02, 2017USD ($)	Oct. 02, 2016USD ($)	Mar. 27, 2016USD ($)	Dec. 27, 2015USD ($)	Sep. 27, 2015USD ($)	Jun. 28, 2015USD ($)	Mar. 29, 2015CAD	Mar. 29, 2015USD ($)	Sep. 28, 2014USD ($)	Dec. 29, 2013CAD	Oct. 01, 2017USD ($)	Oct. 02, 2016USD ($)	Sep. 27, 2015USD ($)
Business acquisition
Increase (decrease) in contingent consideration													$ (6,900,000)	$ 2,800,000
Contingent earn-out liability		$ 2,400,000					$ 0						2,400,000		$ 0
Aggregate maximum of contingent consideration		8,900,000											8,900,000
Gain (loss) on change in contingent consideration													$ 6,900,000	(2,800,000)
Impairment of goodwill	$ 0						58,100,000
CEG
Business acquisition
Earn-out period								3 years
Increase (decrease) in contingent consideration					$ 1,800,000									1,800,000
Earn-out paid to former owners		$ 1,300,000		$ 2,300,000
Contingent earn-out liability			$ 1,800,000	3,900,000			4,100,000	$ 4,100,000						3,900,000	4,100,000
Aggregate maximum of contingent consideration							9,800,000	9,800,000							9,800,000
Potential earn-out to be paid each year								$ 3,250,000
Estimated potential earn-out (as a percent)								42.00%
Minimum operating income threshold to earn contingent consideration during year one								$ 2,000,000
Minimum operating income threshold to earn contingent consideration during year two								2,300,000
Minimum operating income threshold to earn contingent consideration during year three								2,600,000
Gain (loss) on change in contingent consideration			2,100,000		$ (1,800,000)
Potential maximum earn-out to be paid								9,800,000
Operating income to earn maximum consideration during the first year								4,500,000
Operating income to earn maximum consideration during the second year								4,800,000
Operating income to earn maximum consideration during the third year								$ 5,100,000
Impairment of goodwill			0
Other Acquisitions
Business acquisition
Earn-out paid to former owners														1,000,000
Contingent earn-out liability							$ 0								0
Gain (loss) on change in contingent consideration														(1,000,000)
INDUS
Business acquisition
Earn-out period					2 years
Contingent earn-out liability			0	$ 4,900,000	$ 4,700,000									$ 4,900,000
Aggregate maximum of contingent consideration					8,000,000
Potential earn-out to be paid each year					$ 4,000,000
Estimated potential earn-out (as a percent)					50.00%									59.00%
Minimum operating income threshold to earn contingent consideration during year one			3,200,000		$ 3,200,000
Minimum operating income threshold to earn contingent consideration during year two			3,600,000		3,600,000
Gain (loss) on change in contingent consideration			5,000,000
Operating income to earn maximum consideration during the first year					3,600,000
Operating income to earn maximum consideration during the second year					$ 4,000,000
Impairment of goodwill			$ 0
Caber
Business acquisition
Earn-out period												2 years
Increase (decrease) in contingent consideration											$ 1,000,000				(3,100,000)
Earn-out paid to former owners									CAD 4	$ 3,200,000
Contingent earn-out liability										0		CAD 6.5
Aggregate maximum of contingent consideration | CAD												8
Potential earn-out to be paid each year | CAD												CAD 4
Estimated potential earn-out (as a percent)												81.00%
Minimum operating income threshold to earn contingent consideration during year one | CAD												CAD 4
Minimum operating income threshold to earn contingent consideration during year two | CAD									CAD 4.6			4.6
Gain (loss) on change in contingent consideration						$ 0				$ 3,100,000	(1,000,000)				$ 3,100,000
Potential maximum earn-out to be paid											$ 4,000,000
Operating income to earn maximum consideration during the first year | CAD												4.4
Operating income to earn maximum consideration during the second year | CAD												CAD 5.1
Minimum
Business acquisition
Earn-out period													2 years
Maximum
Business acquisition
Earn-out period													3 years

Mergers and Acquisitions - Chan

Mergers and Acquisitions - Changes in the Carrying Value of Estimated Contingent Earn-Out Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Estimated contingent earn-out liabilities
Beginning balance (at fair value)	$ 8,757	$ 4,169	$ 7,030
Estimated earn-out liabilities for acquisitions during the fiscal year	1,604	4,745	4,100
Increases due to re-measurement of fair value reported in interest expense	260	271	136
Net increase (decrease) due to re-measurement of fair value reported as losses (gains) in operating income	(6,923)	2,823	(3,113)
Foreign exchange impact	59	0	(785)
Earn-out payments:
Reported as cash used in operating activities	0	0	0
Reported as cash used in financing activities	(1,319)	(3,251)	(3,199)
Ending balance (at fair value)	$ 2,438	$ 8,757	$ 4,169

Goodwill and Intangible Asset61

Goodwill and Intangible Assets - Schedule of Carrying Value of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016
Goodwill [Roll Forward]
Balance at beginning of the period	$ 717,988	$ 601,379
Goodwill additions	7,055	107,618
Goodwill adjustments	705	1,687
Foreign exchange translation	15,138	7,304
Balance at end of the period	740,886	717,988
WEI
Goodwill [Roll Forward]
Balance at beginning of the period	221,953	210,748
Goodwill additions	0	9,080
Goodwill adjustments	13,509	0
Foreign exchange translation	6,273	2,125
Balance at end of the period	241,735	221,953
RME
Goodwill [Roll Forward]
Balance at beginning of the period	496,035	390,631
Goodwill additions	7,055	98,538
Goodwill adjustments	(12,804)	1,687
Foreign exchange translation	8,865	5,179
Balance at end of the period	$ 499,151	$ 496,035

Goodwill and Intangible Asset62

Goodwill and Intangible Assets - Narrative (Details)	Jul. 03, 2017USD ($)reporting_unit	Jun. 30, 2014	Sep. 27, 2015USD ($)	Oct. 01, 2017USD ($)	Oct. 02, 2016USD ($)	Sep. 27, 2015USD ($)
Goodwill [Line Items]
Impairment of goodwill	$ 0		$ 58,100,000
Number of reporting units having fair value in excess of carrying value of less than 20%. | reporting_unit	0
Impairment of goodwill and other intangible assets			60,800,000	$ 0	$ 0	$ 60,763,000
Impairment of goodwill and other intangible assets, net of tax			57,300,000
Identifiable intangible assets that were determined not to be recoverable			$ 2,700,000
Minimum
Goodwill [Line Items]
Percentage of excess of fair value over carrying value	20.00%
WEI
Goodwill [Line Items]
Gross amounts of goodwill				324,100,000	304,400,000
Accumulated impairment				82,400,000	82,400,000
RME
Goodwill [Line Items]
Gross amounts of goodwill				532,400,000	529,200,000
Accumulated impairment				$ 33,200,000	$ 33,200,000
GMP | RME
Goodwill [Line Items]
Percentage of decline in revenue			25.00%
Annual revenue growth rate (as a percent)		3.00%

Goodwill and Intangible Asset63

Goodwill and Intangible Assets - Amortization (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Finite-lived intangible assets
Gross Amount	$ 118,995	$ 144,044
Accumulated Amortization	(92,307)	(95,082)
Foreign currency translation adjustments	(100)	(1,100)
Amortization expense for intangible assets	22,800	22,100	$ 20,200
Estimated amortization expense
2,018	14,548
2,019	7,034
2,020	2,802
2,021	1,664
2,022	411
Beyond	229
Total	$ 26,688
Non-compete agreements
Finite-lived intangible assets
Weighted- Average Remaining Life (in years)	1 month 6 days
Gross Amount	$ 495	881
Accumulated Amortization	$ (493)	(840)
Client relations
Finite-lived intangible assets
Weighted- Average Remaining Life (in years)	2 years 10 months 24 days
Gross Amount	$ 90,297	112,367
Accumulated Amortization	$ (75,074)	(83,514)
Backlog
Finite-lived intangible assets
Weighted- Average Remaining Life (in years)	1 year 4 months 24 days
Gross Amount	$ 21,518	23,018
Accumulated Amortization	$ (13,301)	(7,536)
Technology and trade names
Finite-lived intangible assets
Weighted- Average Remaining Life (in years)	3 years 3 months 18 days
Gross Amount	$ 6,685	7,778
Accumulated Amortization	$ (3,439)	$ (3,192)

Property and Equipment (Details

Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Property and Equipment
Property and equipment, gross	$ 181,395	$ 214,694
Accumulated depreciation	(124,560)	(146,867)
Property and equipment, net	56,835	67,827
Depreciation expense related to property and equipment	22,207	22,756	$ 23,110
Land and buildings
Property and Equipment
Property and equipment, gross	3,680	3,683
Equipment, furniture and fixtures
Property and Equipment
Property and equipment, gross	150,026	180,750
Leasehold improvements
Property and Equipment
Property and equipment, gross	$ 27,689	$ 30,261

Income Taxes - Summary (Details

Income Taxes - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Income before income taxes:
United States	$ 166,074	$ 113,576	$ 118,822
Foreign	5,687	10,890	(38,501)
Total income before income taxes	171,761	124,466	80,321
Current:
Federal	45,604	22,277	23,836
State	8,860	5,634	5,072
Foreign	9,337	6,651	3,773
Total current income tax expense	63,801	34,562	32,681
Deferred:
Federal	(4,251)	6,231	7,218
State	(945)	(16)	2,335
Foreign	(4,761)	(164)	(1,141)
Total deferred income tax expense	(9,957)	6,051	8,412
Total income tax expense	$ 53,844	$ 40,613	$ 41,093
Reconciliation of effective income tax rate
Tax at federal statutory rate (as a percent)	35.00%	35.00%	35.00%
State taxes, net of federal benefit (as a percent)	3.40%	3.10%	5.00%
Research and Development (R&D) credit (as a percent)	(1.80%)	(3.40%)	(3.80%)
Domestic production deduction (as a percent)	(0.70%)	(0.70%)	(0.80%)
Tax differential on foreign earnings (as a percent)	(0.00%)	(1.60%)	(3.80%)
Non-taxable foreign interest income (as a percent)	(2.90%)	(3.90%)	(5.90%)
Non-deductible executive compensation (as a percent)	0.00%	2.00%	0.00%
Goodwill and contingent consideration (as a percent)	0.00%	0.00%	19.20%
Stock compensation (as a percent)	(2.80%)	0.30%	0.50%
Valuation allowance (as a percent)	(0.50%)	2.40%	5.70%
Change in uncertain tax positions (as a percent)	1.80%	(2.00%)	0.00%
Other (as a percent)	(0.20%)	1.40%	0.10%
Total income tax expense (as a percent)	31.30%	32.60%	51.20%

Income Taxes - Acquisition and

Income Taxes - Acquisition and integration expenses information (Details) - USD ($)	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effective tax rate (as a percent)	31.30%	32.60%	51.20%
Effective income tax rate excluding R&D credits, acquisition expenses and debt pre-payment fees (as a percent)	34.20%	30.90%
Tax benefit recognized based on IRS examination and settlement.	$ 1,200,000
Payments made to tax authorities	23,000,000
Acquisition and integration expenses and debt pre-payment fees		$ 13,300,000
Income tax benefit on business combination acquisition and integration expenses and debt pre-payment fees		0
Business combination acquisition related expenses		6,400,000
Business combination integration costs and debt pre-payment fees		6,900,000
R&D credits		$ 2,000,000
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess tax benefit	$ 4,900,000

Income Taxes - Schedule of temp

Income Taxes - Schedule of temporary differences comprising the net deferred income tax liability (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016
Deferred Tax Assets:
State taxes	$ 598	$ 697
Reserves and contingent liabilities	2,941	2,539
Allowance for doubtful accounts	4,273	3,817
Accrued liabilities	22,466	24,663
Stock-based compensation	10,069	10,684
Intangibles	0	0
Loss carry-forwards	28,261	23,514
Valuation allowance	(25,326)	(25,447)
Total deferred tax assets	43,282	40,467
Deferred Tax Liabilities:
Unbilled revenue	(46,408)	(54,638)
Prepaid expense	(6,253)	(2,921)
Intangibles	(24,328)	(33,268)
Property and equipment	(8,311)	(9,358)
Total deferred tax liability	(85,300)	(100,185)
Net deferred tax liabilities	(42,018)	$ (59,718)
Undistributed earnings of foreign subsidiaries	68,400
Incremental federal tax due to repatriation of foreign earnings	6,200
Unrecognized tax benefits that would affect the effective tax rate, if recognized	$ 9,300
Period during which unrecognized tax benefits would affect the effective tax rate	12 months
State | Expiration dates through 2036
Deferred Tax Liabilities:
Net operating loss carry forwards which expire at various dates	$ 43,700
Foreign
Deferred Tax Liabilities:
Net operating loss carry forwards which have no expiration date	64,000
Foreign | Expiration dates through 2036
Deferred Tax Liabilities:
Net operating loss carry forwards which expire at various dates	28,800
Net operating loss carryforwards	$ 92,900

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Reconciliation of unrecognized tax benefits [Roll Forward]
Beginning balance	$ 22,786	$ 21,618	$ 21,717
Additions for current year tax positions	1,060	2,802	1,147
Additions for prior year tax positions	2,365	1,466	2,309
Reductions for prior year tax positions	(6,875)	(3,100)	(23)
Settlements	(9,999)	0	(3,532)
Ending balance	9,337	22,786	$ 21,618
Accrued additional interest expense	400	200
Reduction in accrued interest	900	0
Amount of interest and penalties accrued	$ 1,100	$ 1,000

Long-Term Debt - Schedule of Lo

Long-Term Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Thousands	Oct. 01, 2017	Oct. 02, 2016
Long-term debt
Total long-term debt	$ 356,871	$ 347,011
Less: Current portion of long-term debt	(15,588)	(15,510)
Long-term debt, less current portion	341,283	331,501
Credit facilities
Long-term debt
Total long-term debt	356,438	346,813
Other
Long-term debt
Total long-term debt	$ 433	$ 198

Long-Term Debt - Narrative (Det

Long-Term Debt - Narrative (Details) AUD in Millions	May 29, 2015USD ($)	Oct. 01, 2017USD ($)Institution	Apr. 30, 2017AUD	Apr. 30, 2016AUD	May 07, 2013USD ($)
Long-term debt
Number of banks with whom entity entered into agreement | Institution		4
Amount outstanding under credit facility		$ 356,400,000
Credit Agreement
Long-term debt
Maximum borrowing capacity	$ 654,800,000
Term of borrowings	5 years
Borrowings outstanding		$ 356,400,000
Weighted-average interest rate (as a percent)		2.45%
Weighted-average rate including the effects of interest rate swap agreement (as a percent)		2.65%
Consolidated leverage ratio		1.62
Consolidated fixed charge coverage ratio		2.27
Credit Agreement | Maximum
Long-term debt
Covenant maximum consolidated leverage ratio	3
Credit Agreement | Minimum
Long-term debt
Covenant minimum consolidated fixed charge coverage ratio	1.25
Credit Agreement | Base rate
Long-term debt
Margin spread on variable rate basis, low end of the range (as a percent)	0.15%
Margin spread on variable rate basis, high end of the range (as a percent)	1.00%
Credit Agreement | Base rate | U.S. federal funds base rate
Long-term debt
Basis spread on variable rate (as a percent)	0.50%
Interest rate basis	U.S. federal funds rate
Credit Agreement | Base rate | Eurocurrency base rate
Long-term debt
Basis spread on variable rate (as a percent)	1.00%
Interest rate basis	Eurocurrency rate
Credit Agreement | Base rate | Bank's prime rate
Long-term debt
Basis spread on variable rate (as a percent)	1.00%
Interest rate basis	bank's prime rate
Credit Agreement | Eurocurrency rate | Eurocurrency base rate
Long-term debt
Margin spread on variable rate basis, low end of the range (as a percent)	1.15%
Margin spread on variable rate basis, high end of the range (as a percent)	2.00%
Interest rate basis	Eurocurrency rate
Credit facility.
Long-term debt
Maximum borrowing capacity | AUD			AUD 30	AUD 30
Amount outstanding under credit facility		$ 0
Standby letters of credit under letter of credit agreements
Long-term debt
Letters of credit outstanding		23,900,000
Term loan facility
Long-term debt
Maximum borrowing capacity	$ 194,800,000				$ 205,000,000
Principal payment due in year 1	10,300,000
Principal payment in year 2	15,400,000
Principal payment in year 3	15,400,000
Principal payment in year 4	15,400,000
Principal payment in year 5	15,400,000
Effective interest rate (as a percent)					1.57%
Borrowings outstanding		161,400,000
Bank guarantees
Long-term debt
Amount outstanding under credit facility		5,600,000
Revolving credit facility
Long-term debt
Maximum borrowing capacity	460,000,000				$ 460,000,000
Borrowings outstanding		195,000,000
Amount available for borrowing under facility		264,000,000
Standby letters of credit
Long-term debt
Maximum borrowing capacity	150,000,000
Letters of credit outstanding		900,000
Swingline loans
Long-term debt
Maximum borrowing capacity	20,000,000
Multicurrency borrowings and letter of credit
Long-term debt
Maximum borrowing capacity	$ 150,000,000
Letters of credit outstanding		$ 4,900,000

Long-Term Debt - Scheduled Matu

Long-Term Debt - Scheduled Maturities of Long-Term Debt (Details) - USD ($) $ in Thousands	Oct. 01, 2017	Oct. 02, 2016
Maturities of Long-term Debt [Abstract]
2,018	$ 15,588
2,019	15,595
2,020	325,688
2,021	0
2,022	0
Beyond	0
Total long-term debt	$ 356,871	$ 347,011

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Leases [Abstract]
Expense associated with operating leases	$ 71.3	$ 75	$ 66.4
Lease contract termination costs		$ 2.9

Leases - Commitments (Details)

Leases - Commitments (Details) $ in Thousands	Oct. 01, 2017USD ($)
Operating lease commitments
2,018	$ 77,854
2,019	62,634
2,020	45,906
2,021	28,740
2,022	17,261
Beyond	21,770
Total	254,165
Capital lease commitments
2,018	158
2,019	211
2,020	0
2,021	0
2,022	0
Beyond	0
Total	369
Less: Amounts representing interest	2
Net present value	$ 367

Leases - Reconciliation of Term

Leases - Reconciliation of Termination Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016
Reconciliation of the beginning and ending balances of liabilities related to contract termination costs
Balance at the beginning of the period	$ 3,104	$ 3,169
Cost transfer between groups		0
Cost incurred and charged to expense		2,167
Adjustments	(1,410)	(2,232)
Balance at the end of the period	1,694	3,104
WEI
Reconciliation of the beginning and ending balances of liabilities related to contract termination costs
Balance at the beginning of the period	1,552	531
Cost transfer between groups		637
Cost incurred and charged to expense		1,418
Adjustments	(1,009)	(1,034)
Balance at the end of the period	543	1,552
RME
Reconciliation of the beginning and ending balances of liabilities related to contract termination costs
Balance at the beginning of the period	1,513	2,461
Cost transfer between groups		(637)
Cost incurred and charged to expense		749
Adjustments	(365)	(1,060)
Balance at the end of the period	1,148	1,513
RCM
Reconciliation of the beginning and ending balances of liabilities related to contract termination costs
Balance at the beginning of the period	39	177
Cost transfer between groups		0
Cost incurred and charged to expense		0
Adjustments	(36)	(138)
Balance at the end of the period	$ 3	$ 39

Stockholders' Equity and Stoc75

Stockholders' Equity and Stock Compensation Plans - Summary (Details) - USD ($)	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Stockholder's equity and stock compensation plans
Vesting period	1 year	1 year
Stock-based compensation and related income tax benefits
Total stock-based compensation	$ 13,450,000	$ 12,964,000	$ 10,926,000
Income tax benefit related to stock-based compensation	(4,715,000)	(4,656,000)	(3,811,000)
Stock-based compensation, net of tax benefit	$ 8,735,000	$ 8,308,000	7,115,000
RSUs
Stockholder's equity and stock compensation plans
Vesting period	4 years	4 years
ESPP
Stockholder's equity and stock compensation plans
Available for future awards	2,373,290
Maximum amount that an employee can contribute during a purchase right period	$ 5,000
Exercise price as percentage of fair market value on the first day of purchase right period	100.00%
Exercise price as percentage of fair market value on the last day of purchase right period	85.00%
Stock-based compensation and related income tax benefits
Total stock-based compensation	$ 500,000	$ 400,000	$ 600,000
2005 EIP | Restricted Stock
Stockholder's equity and stock compensation plans
Vesting period	3 years
2015 EIP
Stockholder's equity and stock compensation plans
Available for future awards	2,600,000
The number every share or unit issued counts against aggregate share limit	3
Grant date prior to March 6, 2006 | 2005 EIP | Stock options
Stockholder's equity and stock compensation plans
Vesting period	4 years
Expiration period	10 years
Grant date prior to March 6, 2006 | 2005 EIP | Stock options | First anniversary of grant date and monthly thereafter
Stockholder's equity and stock compensation plans
Percentage of vesting rights after specified period	25.00%
Grant date on or after March 6, 2006 | 2005 EIP | Stock options
Stockholder's equity and stock compensation plans
Expiration period	8 years
Grant date on or after March 6, 2006 | 2005 EIP | Stock options | Each anniversary of grant date
Stockholder's equity and stock compensation plans
Percentage of vesting rights after specified period	25.00%
Grant date on or after March 6, 2006 | 2005 EIP | RSUs | Each anniversary of grant date
Stockholder's equity and stock compensation plans
Percentage of vesting rights after specified period	25.00%

Stockholders' Equity and Stoc76

Stockholders' Equity and Stock Compensation Plans - Stock Options (Details) - Stock options - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Number of Options (in thousands)
Outstanding at the beginning of the year (in shares)	2,367
Granted (in shares)	183
Exercised (in shares)	(791)
Forfeited (in shares)	(6)
Outstanding at the end of the period (in shares)	1,753	2,367
Vested or expected to vest at the end of the period (in shares)	1,696
Exercisable at the end of the period (in shares)	1,242
Weighted- Average Exercise Price per Share
Outstanding at the beginning of the year (in dollars per share)	$ 24.88
Granted (in dollars per share)	40.67
Exercised (in dollars per share)	44.19
Forfeited (in dollars per share)	17.72
Outstanding at the end of the period (in dollars per share)	27.18	$ 24.88
Vested or expected to vest at the end of the period (in dollars per share)	27.31
Exercisable at the end of the period (in dollars per share)	$ 25.10
Weighted- Average Remaining Contractual Term (in years)
Outstanding at the end of the period	4 years 7 months 2 days
Vested or expected to vest at the end of the period	4 years 6 months
Exercisable at the end of the period	3 years 5 months 5 days
Aggregate Intrinsic Value (in thousands)
Outstanding at the end of the period	$ 33,963
Vested or expected to vest at the end of the period	32,640
Exercisable at the end of the period	$ 26,636
Assumptions used in the Black-Scholes option-pricing model
Dividend yield (as a percent)	1.00%	1.20%	1.00%
Expected stock price volatility, minimum (as a percent)	36.10%	36.10%	36.20%
Expected stock price volatility, maximum (as a percent)	38.80%	38.80%	38.80%
Risk-free rate of return, annual, minimum (as a percent)	1.70%	1.60%	1.50%
Risk-free rate of return, annual, maximum (as a percent)	1.90%	1.80%	1.70%
Unrecognized compensation cost	$ 3,500
Weighted-average period to recognize the unrecognized compensation cost	2 years
Weighted-average fair value of stock options granted (in dollars per share)	$ 12.35	$ 8.05	$ 8.20
Aggregate intrinsic value of options exercised	$ 16,400	$ 7,300	$ 2,300
Net cash proceeds from the exercise of stock options	18,600	18,000	10,800
Income tax benefit realized from exercises of nonqualified stock options and disqualifying dispositions of qualified options	$ 4,900	$ 5,300	$ 3,000

Stockholders' Equity and Stoc77

Stockholders' Equity and Stock Compensation Plans - Restricted Stock (Details) - Restricted Stock - $ / shares	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Number of Shares
Nonvested balance at the beginning of the period (in shares)	35,000
Granted (in shares)	14,000
Vested (in shares)	(49,000)
Forfeited (in shares)	0
Nonvested balance at the end of the period (in shares)	0	35,000
Vested or expected to vest at the end of the period (in shares)	0
Weighted-Average Grant Date Fair Value
Nonvested balance at the beginning of the period (in dollars per share)	$ 28.58
Granted (in dollars per share)	28.58
Vested (in dollars per share)	28.58
Forfeited (in dollars per share)	0
Nonvested balance at the end of the period (in dollars per share)	0	$ 28.58
Vested or expected to vest at the end of the period (in dollars per share)	$ 0
Initially granted (in shares)	0	0	0

Stockholders' Equity and Stoc78

Stockholders' Equity and Stock Compensation Plans - PSUs (Details) - $ / shares	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016
Weighted-Average Grant Date Fair Value
Vesting period	1 year	1 year
PSUs
Number of Shares
Nonvested balance at the beginning of the period (in shares)	277,000
Granted (in shares)	99,180	137,777
Nonvested balance at the end of the period (in shares)	376,000	277,000
Weighted-Average Grant Date Fair Value
Nonvested balance at the beginning of the period (in dollars per share)	$ 31.65
Granted (in dollars per share)	48.36	$ 31.63
Nonvested balance at the end of the period (in dollars per share)	$ 36.05	$ 31.65
Vesting period	3 years	3 years
Percentage of shares that ultimately vest depending on fiscal year earnings per share growth rates	50.00%	50.00%
Percentage of shares that ultimately vest depending on total shareholder return	50.00%	50.00%

Stockholders' Equity and Stoc79

Stockholders' Equity and Stock Compensation Plans - RSUs (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Weighted-Average Grant Date Fair Value
Vesting period	1 year	1 year
Stock-based compensation expense	$ 13,450	$ 12,964	$ 10,926
RSUs
Number of Shares
Nonvested balance at the beginning of the period (in shares)	499,021
Granted (in shares)	226,241	216,539
Vested (in shares)	(186,000)
Forfeited (in shares)	(28,000)
Nonvested balance at the end of the period (in shares)	510,975	499,021
Weighted-Average Grant Date Fair Value
Nonvested balance at the beginning of the period (in dollars per share)	$ 27.16
Granted (in dollars per share)	41	$ 27.14
Vested (in dollars per share)	26.98
Forfeited (in dollars per share)	30.15
Nonvested balance at the end of the period (in dollars per share)	$ 33.19	$ 27.16
Vesting period	4 years	4 years
Restricted Stock Program | Restricted Stock, PSUs and RSUs
Weighted-Average Grant Date Fair Value
Stock-based compensation expense	$ 10,600	$ 10,300	$ 7,500
Unrecognized compensation cost	$ 15,100

Stockholders' Equity and Stoc80

Stockholders' Equity and Stock Compensation Plans - ESPP (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Assumptions used in the Black-Scholes option-pricing model
Stock-based compensation expense	$ 13,450	$ 12,964	$ 10,926
ESPP
Stockholder's equity and stock compensation plans
Shares purchased (in shares)	190	209	243
Weighted-average purchase price (in dollars per share)	$ 26.02	$ 22.54	$ 21.44
Cash received from exercise of purchase rights	$ 4,940	$ 4,707	$ 5,204
Aggregate intrinsic value	$ 0	$ 710	$ 1,277
Assumptions used in the Black-Scholes option-pricing model
Dividend yield (as a percent)	1.00%	1.30%	1.10%
Expected stock price volatility (as a percent)	22.40%	23.70%	23.70%
Risk-free rate of return, annual (as a percent)	0.90%	0.20%	0.20%
Expected life (in years)	1 year	1 year	1 year
Stock-based compensation expense	$ 500	$ 400	$ 600
Unrecognized compensation cost	100	$ 100
Accumulated amount by participants to purchase the entity's common stock	$ 3,100

Retirement Plans (Details)

Retirement Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Retirement Benefits [Abstract]
Minimum service period for employee to participate in the defined contribution plans	1 year
Employer contributions to the plans	$ 11.4	$ 10.7	$ 9.8
Assets related to deferred compensation plans	25	20.9
Liabilities related to deferred compensation plans	$ 25.2	$ 20.8

Earnings Per Share - Calculatio

Earnings Per Share - Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Oct. 01, 2017	Jul. 02, 2017	Apr. 02, 2017	Jan. 01, 2017	Oct. 02, 2016	Jun. 26, 2016	Mar. 27, 2016	Dec. 27, 2015	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Number of weighted-average shares used to compute basic and diluted EPS:
Net income attributable to Tetra Tech	$ 34,467	$ 29,983	$ 26,862	$ 26,562	$ 31,106	$ 25,694	$ 3,744	$ 23,239	$ 117,874	$ 83,783	$ 39,074
Weighted-average common shares outstanding – basic	56,338	57,184	57,270	57,099	57,309	57,796	58,451	59,058	56,911	58,186	60,913
Effect of diluted stock options and unvested restricted stock									1,002	780	619
Weighted-average common stock outstanding – diluted	57,326	58,161	58,270	58,145	58,192	58,616	59,131	59,793	57,913	58,966	61,532
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 0.61	$ 0.52	$ 0.47	$ 0.47	$ 0.54	$ 0.44	$ 0.06	$ 0.39	$ 2.07	$ 1.44	$ 0.64
Diluted (in dollars per share)	$ 0.60	$ 0.52	$ 0.46	$ 0.46	$ 0.53	$ 0.44	$ 0.06	$ 0.39	$ 2.04	$ 1.42	$ 0.64

Earnings Per Share - Antidiluti

Earnings Per Share - Antidilutive Securities (Details) - shares	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Stock options
Antidilutive securities
Securities excluded from the calculation of dilutive potential common shares	0	0	1,000,000

Derivative Financial Instrume84

Derivative Financial Instruments - General Information (Details)	3 Months Ended	12 Months Ended
	Dec. 29, 2013agreement	Oct. 01, 2017USD ($)instrument	Oct. 02, 2016USD ($)instrument	Sep. 29, 2013agreement	Sep. 27, 2015instrument
Not designated as hedging instruments
Derivative financial instruments
Number of derivative instruments | instrument		0	0		0
Foreign currency forward contracts and interest rate swap agreements | Derivatives designated as hedging instruments
Derivative financial instruments
Ineffective portion of derivative instruments		$ 0	$ 0
Amounts excluded from effectiveness testing		0	0
Interest rate swap agreements | Designated as cash flow hedges | Derivatives designated as hedging instruments
Derivative financial instruments
Number of derivative agreements | agreement	2			3
Amount of effective portion of derivatives before tax effect		$ (50,000)	1,600,000
Period of reclassification from accumulated other comprehensive income to interest expense		12 months
Amount expected to be reclassified from accumulated other comprehensive income to interest expense		$ (50,000)	$ 1,600,000
Interest rate swap agreement bearing fixed rate 1.36% | Designated as cash flow hedges | Derivatives designated as hedging instruments
Derivative financial instruments
Notional Amount		$ 40,359,000
Fixed Rate (as a percent)		1.36%
Interest rate swap agreement bearing fixed rate 1.34% | Designated as cash flow hedges | Derivatives designated as hedging instruments
Derivative financial instruments
Notional Amount		$ 40,359,000
Fixed Rate (as a percent)		1.34%
Interest rate swap agreement bearing fixed rate 1.35% | Designated as cash flow hedges | Derivatives designated as hedging instruments
Derivative financial instruments
Notional Amount		$ 40,359,000
Fixed Rate (as a percent)		1.35%
Interest rate swap agreement bearing fixed rate 1.23% | Designated as cash flow hedges | Derivatives designated as hedging instruments
Derivative financial instruments
Notional Amount		$ 20,180,000
Fixed Rate (as a percent)		1.23%
Interest rate swap agreement bearing fixed rate 1.24% | Designated as cash flow hedges | Derivatives designated as hedging instruments
Derivative financial instruments
Notional Amount		$ 20,180,000
Fixed Rate (as a percent)		1.24%

Derivative Financial Instrume85

Derivative Financial Instruments - Table (Details) - USD ($) $ in Thousands	Oct. 01, 2017	Oct. 02, 2016
Interest rate swap agreements | Derivatives designated as hedging instruments | Designated as cash flow hedges | Other current liabilities
Derivative financial instruments
Derivative liabilities, Fair Value of Derivative Instruments	$ 49	$ (1,572)

Reclassifications Out of Accu86

Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016
Reclassifications out of accumulated other comprehensive income (loss)
Balance at the beginning of the period	$ 869,259
Other comprehensive income before reclassifications	30,257	$ 17,107
Amounts reclassified from accumulated other comprehensive income	(749)	(1,944)
Net current-period other comprehensive income	29,508	15,163
Balance at the end of the period	928,453	869,259
Foreign Currency Translation Adjustments
Reclassifications out of accumulated other comprehensive income (loss)
Balance at the beginning of the period	(126,840)	(141,229)
Other comprehensive income before reclassifications	27,894	14,389
Amounts reclassified from accumulated other comprehensive income	0	0
Net current-period other comprehensive income	27,894	14,389
Balance at the end of the period	(98,946)	(126,840)
Gain (Loss) on Derivative Instruments
Reclassifications out of accumulated other comprehensive income (loss)
Balance at the beginning of the period	(1,168)	(1,942)
Other comprehensive income before reclassifications	2,363	2,718
Amounts reclassified from accumulated other comprehensive income	(749)	(1,944)
Net current-period other comprehensive income	1,614	774
Balance at the end of the period	446	(1,168)
Accumulated Other Comprehensive Income (Loss)
Reclassifications out of accumulated other comprehensive income (loss)
Balance at the beginning of the period	(128,008)	(143,171)
Balance at the end of the period	$ (98,500)	$ (128,008)

Fair Value Measurements (Detail

Fair Value Measurements (Details) $ in Millions	Oct. 01, 2017USD ($)
Fair Value Disclosures [Abstract]
Net borrowing under credit agreement	$ 356.4

Reportable Segments - Financial

Reportable Segments - Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Oct. 01, 2017	Jul. 02, 2017	Apr. 02, 2017	Jan. 01, 2017	Oct. 02, 2016	Jun. 26, 2016	Mar. 27, 2016	Dec. 27, 2015	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Financial information concerning reportable segments
Revenue	$ 735,188	$ 685,539	$ 663,781	$ 668,851	$ 728,508	$ 666,869	$ 627,384	$ 560,708	$ 2,753,360	$ 2,583,469	$ 2,299,321
Operating Income (Loss)	54,647	$ 45,884	$ 42,956	$ 39,855	47,190	$ 39,085	$ 16,650	$ 32,930	183,342	135,855	87,684
Depreciation									22,207	22,756	23,110
Amortization expense for intangible assets									22,800	22,100	20,200
Fair value adjustments to contingent consideration liabilities									6,923	(2,823)	3,113
Acquisition and integration expenses									0	19,548	0
Total Assets	1,902,745				1,800,779				1,902,745	1,800,779
Operating segments | WEI
Financial information concerning reportable segments
Revenue									1,146,366	1,028,281	993,631
Operating Income (Loss)									117,894	95,996	93,142
Depreciation									4,690	4,797	5,335
Total Assets	354,709				308,438				354,709	308,438
Operating segments | RME
Financial information concerning reportable segments
Revenue									1,666,364	1,569,702	1,282,046
Operating Income (Loss)									111,122	112,202	93,359
Depreciation									15,142	15,703	13,342
Total Assets	555,485				522,895				555,485	522,895
Operating segments | RCM
Financial information concerning reportable segments
Revenue									18,207	52,150	86,575
Operating Income (Loss)									(14,712)	(11,834)	(8,614)
Depreciation									1,062	736	1,801
Total Assets	33,620				39,107				33,620	39,107
Elimination of inter-segment revenue
Financial information concerning reportable segments
Revenue									(77,577)	(66,664)	(62,931)
Corporate
Financial information concerning reportable segments
Operating Income (Loss)									(30,962)	(60,509)	(90,203)
Depreciation									1,313	1,520	2,632
Impairment charge											60,800
Amortization expense for intangible assets									22,800	22,100	20,200
Fair value adjustments to contingent consideration liabilities									6,900	(2,800)	$ 3,100
Acquisition and integration expenses										19,500
Total Assets	$ 958,931				$ 930,339				$ 958,931	$ 930,339

Reportable Segments - Geographi

Reportable Segments - Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Oct. 01, 2017	Jul. 02, 2017	Apr. 02, 2017	Jan. 01, 2017	Oct. 02, 2016	Jun. 26, 2016	Mar. 27, 2016	Dec. 27, 2015	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Reportable Segments
Revenue	$ 735,188	$ 685,539	$ 663,781	$ 668,851	$ 728,508	$ 666,869	$ 627,384	$ 560,708	$ 2,753,360	$ 2,583,469	$ 2,299,321
United States
Reportable Segments
Revenue									2,018,841	1,858,551	1,734,439
Long-Lived Assets	58,965				59,334				58,965	59,334	61,526
Foreign countries
Reportable Segments
Revenue									734,519	724,918	564,882
Long-Lived Assets	$ 34,183				$ 39,067				$ 34,183	$ 39,067	$ 32,230

Reportable Segments - Revenue b

Reportable Segments - Revenue by Sector (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Oct. 01, 2017	Jul. 02, 2017	Apr. 02, 2017	Jan. 01, 2017	Oct. 02, 2016	Jun. 26, 2016	Mar. 27, 2016	Dec. 27, 2015	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Revenue by client sector
Threshold percentage for disclosure of revenue from a single client									10.00%	10.00%	10.00%
Revenue	$ 735,188	$ 685,539	$ 663,781	$ 668,851	$ 728,508	$ 666,869	$ 627,384	$ 560,708	$ 2,753,360	$ 2,583,469	$ 2,299,321
International
Revenue by client sector
Revenue									734,519	724,918	564,882
U.S. commercial
Revenue by client sector
Revenue									764,643	763,443	736,815
U.S. federal government
Revenue by client sector
Revenue									901,136	784,368	709,600
U.S. state and local government
Revenue by client sector
Revenue									$ 353,062	$ 310,740	$ 288,024

Quarterly Financial Informati91

Quarterly Financial Information-Unaudited (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Oct. 01, 2017	Jul. 02, 2017	Apr. 02, 2017	Jan. 01, 2017	Oct. 02, 2016	Jun. 26, 2016	Mar. 27, 2016	Dec. 27, 2015	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Business acquisition
Acquisition and integration expenses									$ 0	$ 19,548	$ 0
Revenue	$ 735,188	$ 685,539	$ 663,781	$ 668,851	$ 728,508	$ 666,869	$ 627,384	$ 560,708	2,753,360	2,583,469	2,299,321
Operating income	54,647	45,884	42,956	39,855	47,190	39,085	16,650	32,930	183,342	135,855	87,684
Net income attributable to Tetra Tech	$ 34,467	$ 29,983	$ 26,862	$ 26,562	$ 31,106	$ 25,694	$ 3,744	$ 23,239	$ 117,874	$ 83,783	$ 39,074
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 0.61	$ 0.52	$ 0.47	$ 0.47	$ 0.54	$ 0.44	$ 0.06	$ 0.39	$ 2.07	$ 1.44	$ 0.64
Diluted (in dollars per share)	$ 0.60	$ 0.52	$ 0.46	$ 0.46	$ 0.53	$ 0.44	$ 0.06	$ 0.39	$ 2.04	$ 1.42	$ 0.64
Weighted-average common shares outstanding:
Basic (in shares)	56,338	57,184	57,270	57,099	57,309	57,796	58,451	59,058	56,911	58,186	60,913
Diluted (in shares)	57,326	58,161	58,270	58,145	58,192	58,616	59,131	59,793	57,913	58,966	61,532
Coffey
Business acquisition
Acquisition and integration expenses					$ 2,600	$ 1,000	$ 15,900			$ 19,500
Coffey | Interest expense
Business acquisition
Pre-payment charges paid							$ 1,900			$ 1,900

SCHEDULE II-VALUATION AND QUA92

SCHEDULE II-VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Sep. 27, 2015
Allowance for doubtful accounts
Changes in valuation and qualifying accounts and reserves
Balance at Beginning of Period	$ 35,233	$ 31,490	$ 39,780
Charged to Costs, Expenses and Revenue	2,848	8,082	(1,034)
Deductions	(6,233)	(12,191)	(5,965)
Other	411	7,852	(1,291)
Balance at End of Period	32,259	35,233	31,490
Income tax valuation allowance
Changes in valuation and qualifying accounts and reserves
Balance at Beginning of Period	25,447	7,791	7,576
Charged to Costs, Expenses and Revenue	(121)	3,856	4,609
Deductions	0	0	0
Other	0	13,800	(4,394)
Balance at End of Period	$ 25,326	$ 25,447	$ 7,791