Tetra Tech (TTEK) 10-Q 1 May 15 2015 Q2 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	6 Months Ended
	Mar. 29, 2015	Apr. 27, 2015
Document and Entity Information
Entity Registrant Name	TETRA TECH INC
Entity Central Index Key	831641
Document Type	10-Q
Document Period End Date	29-Mar-15
Amendment Flag	FALSE
Current Fiscal Year End Date	-18
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		60,259,015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q2

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Mar. 29, 2015	Sep. 28, 2014
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$98,518	$122,379
Accounts receivable - net	666,013	701,892
Prepaid expenses and other current assets	48,657	52,256
Income taxes receivable	18,392	22,076
Total current assets	831,580	898,603
Property and equipment - net	65,107	73,864
Investments in and advances to unconsolidated joint ventures	2,159	2,140
Goodwill	671,397	714,190
Intangible assets - net	49,062	63,095
Other long-term assets	24,642	24,512
Total assets	1,643,947	1,776,404
Current liabilities:
Accounts payable	136,319	175,952
Accrued compensation	89,423	110,186
Billings in excess of costs on uncompleted contracts	95,270	103,343
Deferred income taxes	21,778	20,387
Current portion of long-term debt	10,805	10,989
Estimated contingent earn-out liabilities		3,568
Other current liabilities	73,499	79,436
Total current liabilities	427,094	503,861
Deferred income taxes	27,287	28,786
Long-term debt	228,007	192,842
Long-term estimated contingent earn-out liabilities		3,462
Other long-term liabilities	38,655	34,397
Commitments and contingencies
Equity:
Preferred stock - Authorized, 2,000 shares of $0.01 par value; no shares issued and outstanding at March 29, 2015, and September 28, 2014
Common stock - Authorized, 150,000 shares of $0.01 par value; issued and outstanding, 60,333 and 62,591 shares at March 29, 2015, and September 28, 2014, respectively	603	626
Additional paid-in capital	346,863	402,516
Accumulated other comprehensive loss	-112,620	-42,538
Retained earnings	687,437	651,475
Tetra Tech stockholders' equity	922,283	1,012,079
Noncontrolling interests	621	977
Total equity	922,904	1,013,056
Total liabilities and equity	$1,643,947	$1,776,404

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 29, 2015	Sep. 28, 2014
In Thousands, except Per Share data, unless otherwise specified
Condensed Consolidated Balance Sheets
Preferred stock, Authorized shares	2,000	2,000
Preferred stock, par value (in dollars per share)	$0.01	$0.01
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, Authorized shares	150,000	150,000
Common stock, par value (in dollars per share)	$0.01	$0.01
Common stock, shares issued	60,333	62,591
Common stock, shares outstanding	60,333	62,591

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Income (USD $)	3 Months Ended		6 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 29, 2015	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014
Condensed Consolidated Statements of Income
Revenue	$564,763	$586,285	$1,145,819	$1,232,133
Subcontractor costs	-132,009	-130,300	-275,985	-293,158
Other costs of revenue	-362,957	-386,913	-721,238	-783,442
Selling, general and administrative expenses	-42,512	-44,229	-84,699	-91,602
Contingent consideration - fair value adjustments	3,113	21,343	3,113	25,973
Operating income	30,398	46,186	67,010	89,904
Interest expense	-1,804	-2,496	-3,594	-4,919
Income before income tax expense	28,594	43,690	63,416	84,985
Income tax expense	-9,584	-11,781	-18,760	-25,749
Net income including noncontrolling interests	19,010	31,909	44,656	59,236
Net loss (income) attributable to noncontrolling interests	7	-200	-64	-213
Net income attributable to Tetra Tech	$19,017	$31,709	$44,592	$59,023
Earnings per share attributable to Tetra Tech:
Basic	$0.31	$0.49	$0.72	$0.91
Diluted	$0.31	$0.48	$0.71	$0.90
Weighted-average common shares outstanding:
Basic	61,153	64,835	61,816	64,670
Diluted	61,723	65,710	62,431	65,517
Cash dividends paid per share	$0.07		$0.14

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 29, 2015	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014
Consolidated Statements of Comprehensive Income
Net income including noncontrolling interests	$19,010	$31,909	$44,656	$59,236
Other comprehensive income, net of tax:
Foreign currency translation adjustments	-43,680	-15,684	-68,189	-37,819
(Loss) gain on cash flow hedge valuations, net of tax	-1,517	-386	-1,997	439
Other comprehensive loss, net of tax	-45,197	-16,070	-70,186	-37,380
Comprehensive income (loss) including noncontrolling interests	-26,187	15,839	-25,530	21,856
Net loss (income) attributable to noncontrolling interests	7	-200	-64	-213
Foreign currency translation adjustments	164	34	104	73
Comprehensive (income) loss attributable to noncontrolling interests	171	-166	40	-140
Comprehensive income (loss) attributable to Tetra Tech	($26,016)	$15,673	($25,490)	$21,716

Condensed_Consolidated_Stateme2

Condensed Consolidated Statements of Cash Flows (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Mar. 29, 2015	Mar. 30, 2014
Cash flows from operating activities:
Net income including noncontrolling interests	$44,656	$59,236
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	23,948	29,414
Equity in earnings of unconsolidated joint ventures	-1,842	-1,492
Distributions of earnings from unconsolidated joint ventures	1,694	1,064
Stock-based compensation	5,391	5,537
Excess tax benefits from stock-based compensation	-165	-677
Deferred income taxes	1,460	-2,658
Provision for doubtful accounts	-1,411	3,634
Fair value adjustments to contingent consideration	-3,113	-25,973
(Gain) loss on disposal of property and equipment	-6,175	717
Foreign exchange loss (gain)	54	-280
Changes in operating assets and liabilities, net of effects of business acquisitions:
Accounts receivable	37,289	5,550
Prepaid expenses and other assets	6,289	-4,101
Accounts payable	-39,634	9,517
Accrued compensation	-20,763	-21,403
Billings in excess of costs on uncompleted contracts	-8,073	6,460
Other liabilities	-20,333	-15,551
Income taxes receivable/payable	5,494	7,212
Net cash provided by operating activities	24,766	56,206
Cash flows from investing activities:
Capital expenditures	-12,096	-11,699
Payments for business acquisitions, net of cash acquired		-10,286
Payment received on note for sale of operation		3,900
Proceeds from sale of property and equipment	9,824	2,957
Net cash used in investing activities	-2,272	-15,128
Cash flows from financing activities:
Payments on long-term debt	-24,001	-459
Proceeds from borrowings	59,095
Payments of earn-out liabilities	-3,199	-9,337
Net change in overdrafts		-915
Excess tax benefits from stock-based compensation	165	677
Repurchases of common stock	-68,735	-6,612
Dividends paid	-8,630
Net proceeds from issuance of common stock	4,316	17,529
Net cash (used in) provided by financing activities	-40,989	883
Effect of foreign exchange rate changes on cash	-5,366	-4,041
Net (decrease) increase in cash and cash equivalents	-23,861	37,920
Cash and cash equivalents at beginning of period	122,379	129,305
Cash and cash equivalents at end of period	98,518	167,225
Cash paid during the year for:
Interest	3,604	4,404
Income taxes, net of refunds received of $1.2 million and $1.7 million	$11,599	$19,973

Condensed_Consolidated_Stateme3

Condensed Consolidated Statements of Cash Flows (Parenthetical) (USD $)	6 Months Ended
In Millions, unless otherwise specified	Mar. 29, 2015	Mar. 30, 2014
Condensed Consolidated Statements of Cash Flows
Income taxes, refunds received	$1.20	$1.70

Basis_of_Presentation

Basis of Presentation	6 Months Ended
	Mar. 29, 2015
Basis of Presentation
Basis of Presentation
	1.Basis of Presentation
	The accompanying unaudited condensed consolidated financial statements and related notes of Tetra Tech, Inc. (“we,” “us” or “our”) have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X.  They do not include all of the information and footnotes required by GAAP for complete financial statements and, therefore, should be read in conjunction with the audited consolidated financial statements and related notes contained in our Annual Report on Form 10-K for the fiscal year ended September 28, 2014.
	These financial statements reflect all normal recurring adjustments that are considered necessary for a fair statement of our financial position, results of operations and cash flows for the interim periods presented.  The results of operations and cash flows for any interim period are not necessarily indicative of results for the full year or for future years.
	Beginning in the first quarter of fiscal 2015, we reorganized our core operations to better align them with our markets, resulting in two renamed reportable segments.  We now 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, mining, waste management, remediation, utilities, and international development services.  We report the results of the wind-down of our non-core construction activities in the Remediation and Construction Management (“RCM”) reportable segment.  Prior year amounts for reportable segments have been revised to conform to the current-year presentation.

Accounts_Receivable_Net_and_Re

Accounts Receivable - Net and Revenue Recognition	6 Months Ended
	Mar. 29, 2015
Accounts Receivable - Net and Revenue Recognition
Accounts Receivable - Net and Revenue Recognition
	2.Accounts Receivable – Net and Revenue Recognition
	Net accounts receivable and billings in excess of costs on uncompleted contracts consisted of the following:
		March 29,		September 28,
		2015		2014
		(in thousands)
	Billed	$	314,993	$	351,693
	Unbilled	359,574		363,050
	Contract retentions	26,008		26,929
	Total accounts receivable – gross	700,575		741,672
	Allowance for doubtful accounts	-34,562		-39,780
	Total accounts receivable – net	$	666,013	$	701,892
	Billings in excess of costs on uncompleted contracts	$	95,270	$	103,343
	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 March 29, 2015 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 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 revenue recognized.  The majority of billings in excess of costs on uncompleted contracts, excluding those related to claims, 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 progresses without obtaining a definitive client agreement.  Unapproved change orders constitute claims 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, 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 March 29, 2015 and September 28, 2014 included approximately $80 million and $79 million, respectively, related to claims, including requests for equitable adjustment, on contracts that provide for price redetermination.  We regularly evaluate all 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, we reduced revenue and operating income by a net $3.0 million in the second quarter of fiscal 2015 as a result of our updated assessment of the collectability of claims with a U.S. state and local government client.  On a year-to-date basis, we have recorded net gains of $0.2 million related to claims.  During both the second quarter and first six months of fiscal 2014, we recognized gains related to settlement of claims of $3.4 million.
	Billed accounts receivable related to U.S. federal government contracts were $59.3 million and $57.4 million at March 29, 2015 and September 28, 2014, respectively.  U.S. federal government unbilled receivables were $68.2 million and $73.2 million at March 29, 2015 and September 28, 2014, respectively.  Other than the U.S. federal government, no single client accounted for more than 10% of our accounts receivable at March 29, 2015 and September 28, 2014.
	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 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 unfavorable operating income adjustments of $3.5 million and $5.9 million during the second quarter and first half of fiscal 2015, respectively, compared to $5.3 million in the comparable periods of last year.  Changes in revenue and cost estimates could also result in a projected loss that would be recorded immediately in earnings.  As of March 29, 2015 and September 28, 2014, we maintained a liability for anticipated losses of $13.6 million and $18.6 million, respectively.  The estimated cost to complete the related contracts as of March 29, 2015 was $83.9 million.

Mergers_and_Acquisitions

Mergers and Acquisitions	6 Months Ended
	Mar. 29, 2015
Mergers and Acquisitions
Mergers and Acquisitions
	3.Mergers and Acquisitions
	We made no acquisitions in the first half of fiscal 2015.  In fiscal 2014, we made immaterial acquisitions that enhanced our service offerings and expanded our geographic presence in our WEI and RME reportable segments.
	Subsequent Event.  On May 1, 2015, we acquired Cornerstone Environmental Group, an environmental engineering and consulting firm focused on solid waste markets in the United States.  The purchase price was not material.
	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.  Specifically, the goodwill additions related to the fiscal 2014 acquisitions primarily represent the value of workforces with distinct expertise in the oil and gas and disaster preparedness 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.  None of the acquisitions were considered material, individually or in the aggregate, to our condensed consolidated financial statements.  As a result, no pro forma information has been provided for the respective periods.
	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 “Estimated contingent earn-out liabilities” and “Long-term estimated 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 (as described in “Critical Accounting Policies and Estimates” in our Annual Report on Form 10-K for the fiscal year ended September 28, 2014).  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.
	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 previous 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 the second quarter and first half of fiscal 2015, we recorded a decrease in 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 (“Caber”), which is part of our Oil, Gas & Energy reporting unit in the 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 would need 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 C$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 on-going 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 recent decline in oil prices.  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 concluded that Caber’s operating income for the second earn-out period, which ends in the first quarter of fiscal 2016, 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.
	In the second quarter and first six months of fiscal 2014, we recorded net decreases in our contingent earn-out liabilities and reported related gains in operating income of $21.3 million and $26.0 million, respectively.  The fiscal 2014 gains primarily resulted from updated valuations of the contingent consideration liability for Parkland Pipeline (“Parkland”), which is part of our Oil, Gas & Energy reporting unit in our RME segment.
	The acquisition agreement for Parkland included a contingent earn-out agreement based on the achievement of operating income thresholds (in Canadian dollars) in each of the first three years beginning on the acquisition date, which was in the second quarter of fiscal 2013.  The maximum earn-out obligation over the three-year earn-out period was C$56.0 million (C$12.0 million, C$22.0 million and C$22.0 million in earn-out years one, two and three, respectively).  These 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 C$56.0 million.  Parkland was required to meet a minimum operating income threshold in each year in order to earn any contingent consideration.  These thresholds were C$34.7 million, C$38.2 million and C$41.9 million in years one, two and three, respectively.  In order to earn the maximum contingent consideration, Parkland would need to generate operating income of C$42.5 million in year one, C$46.4 million in year two, and C$50.6 million in year three.
	The determination of the fair value of the purchase price for Parkland 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 Parkland’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 Parkland’s contingent earn-out liability of C$46.8 million in the second quarter of fiscal 2013.  In determining that Parkland would attain 84% of the maximum potential earn-out, we considered several factors including Parkland’s recent historical revenue and operating income levels and growth rates, the recent trend in Parkland’s backlog level, and the prospects for the midstream oil and gas industry in Western Canada.
	In fiscal 2014, we recorded decreases in our contingent earn-out liability for Parkland and reported related net gains in operating income of $44.6 million.  These gains resulted from Parkland’s actual and projected post-acquisition performance falling below our initial expectations concerning the likelihood and timing of achieving the relevant operating income thresholds.  The remaining difference compared to the initial value was due to currency translation, and the related liability was $0 at the end of fiscal 2014.
	In the second quarter of fiscal 2014, we updated the estimated cost to complete a large fixed-price contract at Parkland, and determined that the project would be break-even compared to the significant profit estimated the previous quarter when the project was initiated.  As a result, during the second quarter of fiscal 2014 we reversed $5.3 million of profit previously recognized on the project.  This variance, and our updated estimate that the revenue for the remainder of the project would produce no operating income, resulted in our conclusion that Parkland’s operating income in the first and second earn-out periods would fall below the minimum operating income thresholds in each such year.  As a result, we reduced the contingent earn-out liability for the first and second earn-out periods to $0, which resulted in gains totaling $24.7 million ($5.6 million and $19.1 million in the first and second quarters of fiscal 2014, respectively).
	In the fourth quarter of fiscal 2014, we updated our projection of Parkland’s operating income for the third earn-out period.  This assessment included a review of the projects in Parkland’s backlog, the inventory of prospective new contract awards, and the forecast for economic activity in the Western Canada oil and gas sector.  As a result of this assessment, we concluded that Parkland’s operating income in the third earn-out period would be lower than our original estimate at the acquisition date and would fall below the minimum operating income threshold.  As a result, we reduced the remaining contingent earn-out liability balance for the third earn-out period to $0, which resulted in a gain of $19.9 million.
	Each time we determined that Parkland’s and Caber’s operating income would be lower than our original estimate at the acquisition date, we also evaluated the related goodwill for potential impairment.  In each case, we determined that the lower income projections were the result of temporary events, and did not negatively impact the reporting unit’s longer term performance or result in a goodwill impairment.
	At March 29, 2015, there was a total maximum of $20.6 million of outstanding contingent consideration related to acquisitions.  Of this amount, there were no accruals on our condensed consolidated balance sheet.  In the first half of fiscal 2015, we made $3.2 million of earn-out payments to former owners, and reported this amount as cash used in financing activities.  In the first half of fiscal 2014, we made $10.6 million of earn-out payments to former owners.  Of this amount, we reported $9.3 million as cash used in financing activities and $1.3 million as cash used in operating activities.

Goodwill_and_Intangible_Assets

Goodwill and Intangible Assets	6 Months Ended
	Mar. 29, 2015
Goodwill and Intangible Assets
Goodwill and Intangible Assets
	4.Goodwill and Intangible Assets
	Effective September 29, 2014, we reorganized our core operations into our WEI and RME reportable segments.  The results of the wind-down of our non-core construction activities are reported in the RCM reportable segment.  Prior year amounts for reportable segments have been revised to conform to the current-year presentation.
	The following table summarizes the changes in the carrying value of goodwill:
		WEI			RME			Total
		(in thousands)
	Balance at September 28, 2014	$	238,086		$	476,104		$	714,190
	Foreign exchange translation	-15,528			-27,265			-42,793
	Balance at March 29, 2015	$	222,558		$	448,839		$	671,397
	We perform our annual goodwill impairment review at the beginning of our fiscal fourth quarter.  Our most recent review at June 30, 2014 (i.e. the first day of our fourth quarter in fiscal 2014), 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.
	The reorganization of our core operations, described further in Note 10, “Reportable Segments”, also impacted the definition of our reporting units used for goodwill impairment testing.  As a result, as of September 29, 2014, we performed impairment testing for goodwill under our new segment structure and determined that the estimated fair value of each reporting unit exceeded its corresponding carrying amount including recorded goodwill, and, as such, no impairment existed as of September 29, 2014.  However, our Global Mining Practice (“GMP”) reporting unit, which is part of our RME reportable segment, had an estimated fair value that exceeded its carrying value by less than 20%.
	We estimate the fair value of all reporting units with a goodwill balance based on a comparison and weighting of the income approach (weighted 70%), specifically the discounted cash flow method and the market approach (weighted 30%), 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.  The resulting fair value is most sensitive to the assumptions we use in our discounted cash flow analysis.  The assumptions that have the most significant impact on the fair value calculation are the reporting unit’s revenue growth rate and operating profit margin, and the discount rate used to convert future estimated cash flows to a single present value amount.
	In our discounted cash flow model for GMP as of September 29, 2014, we assumed annual revenue growth rates of 3% to 5% based on historical trends in GMP and the mining industry, projections for future mining activity, and GMP’s backlog and prospects for new orders.  We discounted the resulting cash flows at a rate of 14%.  Our market-based assessment resulted in a value approximating a 0.7 multiple of revenue, net of subcontractor costs, for the 12 month period preceding the valuation date.  The discounted cash flow value, combined on a weighted-basis with the results of our market analysis, resulted in an estimated fair value for GMP of approximately $102.8 million compared to our carrying value including goodwill of approximately $91.8 million.  As of March 29, 2015, the goodwill amount for GMP was $61.4 million.
	Although we believe that our current estimate of fair value is reasonable, our analysis is primarily dependent on our future level of revenue from our mining clients.  However, the extent of future activity is uncertain, particularly in light of the significant contraction in the mining sector over the last two years.  We currently anticipate that if GMP’s future revenue declines by 20% or more, or market prices for similar businesses decline by more than 15%, GMP’s goodwill could become impaired.
	Additionally, if the yield to maturity on 20-year U.S. treasury bonds (our assumed risk-free rate of return) or the additional return investors require for alternate investments, including those similar to GMP, increases, we may be required to increase the discount rate used in our cash flow analysis.  If all of our operating assumptions remain constant, but we are required to increase the discount rate in our cash flow model to 15.5% or higher, GMP’s goodwill could become impaired.
	Foreign exchange impact relates to our foreign subsidiaries with functional currencies that are different than our reporting currency.  The gross amounts of goodwill for WEI were $253.7 million and $269.2 million at March 29, 2015 and September 28, 2014, respectively, excluding $31.1 million of accumulated impairment.  The gross amounts of goodwill for RME were $475.2 million and $502.5 million at March 29, 2015 and September 28, 2014, respectively, excluding $26.4 million of accumulated impairment.
	The gross amount and accumulated amortization of our acquired identifiable intangible assets with finite useful lives included in “Intangible assets - net” on the condensed consolidated balance sheets, were as follows:
		March 29, 2015								September 28, 2014
		Weighted-		Gross			Accumulated			Gross		Accumulated
		Average		Amount			Amortization			Amount		Amortization
		Remaining Life
		(in Years)
		($ in thousands)
	Non-compete agreements	1.5		$	933		$	-564		$	1,086	$	-524
	Client relations	3.4		113,716			-65,824			122,198		-61,117
	Backlog	–		1,070			-1,070			1,283		-1,072
	Technology and trade names	1.6		2,627			-1,826			2,917		-1,676
	Total			$	118,346		$	-69,284		$	127,484	$	-64,389
	Foreign currency translation adjustments reduced net identifiable intangible assets by $3.3 million in the first half of fiscal 2015.  Amortization expense for the identifiable intangible assets for the three and six months ended March 29, 2015 was $4.8 million and $10.8 million, respectively, compared to $6.7 million and $15.3 million for the prior-year periods.  Estimated amortization expense for the remainder of fiscal 2015 and succeeding years is as follows:
		Amount
		(in thousands)
	2015	$	8,842
	2016	15,616
	2017	13,727
	2018	6,038
	2019	2,832
	Beyond	2,007
	Total	$	49,062

Property_and_Equipment

Property and Equipment	6 Months Ended
	Mar. 29, 2015
Property and Equipment
Property and Equipment
	5.Property and Equipment
	Property and equipment consisted of the following:
		March 29,		September 28,
		2015		2014
		(in thousands)
	Land and buildings	$	3,648	$	4,029
	Equipment, furniture and fixtures	174,056		204,298
	Leasehold improvements	23,047		24,478
	Total property and equipment	200,751		232,805
	Accumulated depreciation	-135,644		-158,941
	Property and equipment, net	$	65,107	$	73,864
	The depreciation expense related to property and equipment, including assets under capital leases, was $5.9 million and $12.8 million for the three and six months ended March 29, 2015, respectively, compared to $6.6 million and $13.7 million for the prior-year periods.  In the first six months of fiscal 2015, we sold assets comprised primarily of equipment of $3.6 million for net proceeds of $9.8 million, and recognized a corresponding gain of $6.2 million.  This equipment was primarily related to our RCM segment.

Stock_Repurchase_and_Dividends

Stock Repurchase and Dividends	6 Months Ended
	Mar. 29, 2015
Stock Repurchase and Dividends.
Stock Repurchase and Dividends
	6.Stock Repurchase and Dividends
	In June 2013, our Board of Directors authorized a stock repurchase program under which we could repurchase up to $100 million of our common stock.  Stock repurchases could be made on the open market or in privately negotiated transactions with third parties.  From the inception of this program through September 28, 2014, we repurchased through open market purchases a total of 3.9 million shares at an average price of $25.59 per share, for a total cost of $100 million.
	On November 10, 2014, the Board of Directors authorized a new stock repurchase program under which we may repurchase up to $200 million of our common stock over the next two years.  In the first half of fiscal 2015, we repurchased through open market purchases a total of 2.7 million shares at an average price of $25.11, for a total cost of $68.7 million under this new repurchase program.
	On November 10, 2014, the Board of Directors declared a quarterly cash dividend of $0.07 per share to stockholders of record as of the close of business on November 26, 2014.  On January 26, 2015, the Board of Directors declared a quarterly cash dividend of $0.07 per share to stockholders of record as of the close of business on February 11, 2015.  A total of $8.6 million was paid in dividends for the first half of fiscal 2015.
	Subsequent Event.  On April 27, 2015, the Board of Directors declared a quarterly cash dividend of $0.08 per share payable on May 29, 2015 to stockholders of record as of the close of business on May 14, 2015.

Stockholders_Equity_and_Stock_

Stockholders' Equity and Stock Compensation Plans	6 Months Ended
	Mar. 29, 2015
Stockholders' Equity and Stock Compensation Plans
Stockholders' Equity and Stock Compensation Plans
	7.Stockholders’ Equity and Stock Compensation Plans
	We recognize the fair value of our stock-based compensation awards as compensation expense on a straight-line basis over the requisite service period in which the award vests.  Stock-based compensation expense for the three and six months ended March 29, 2015 was $2.6 million and $5.4 million, respectively, compared to $3.2 million and $5.5 million for the same periods last year.  The majority of these amounts were included in “Selling, general and administrative (“SG&A”) expenses” in our condensed consolidated statements of income.  There were no material stock compensation awards in the second quarter of fiscal 2015.  For the six months ended March 29, 2015, we granted 266,420 stock options with an exercise price of $27.26 per share and an estimated weighted-average fair value of $8.20 per share.  In addition, we awarded 155,265 performance shares units (“PSUs”) to our non-employee directors and executive officers at the fair value of $27.26 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 diluted earnings per share and 50% on our total shareholder return over the vesting period.  Additionally, we awarded 239,747 restricted stock units (“RSUs”) to our non-employee directors, executive officers and employees at the fair value of $27.26 per share on the award date.  All of the executive officer and employee RSUs have time-based vesting over a four-year period, and the non-employee director RSUs vest after one year.

Earnings_Per_Share_EPS

Earnings Per Share ("EPS")	6 Months Ended
	Mar. 29, 2015
Earnings Per Share ("EPS")
Earnings Per Share ("EPS")
	8.Earnings Per Share (“EPS”)
	Basic EPS is computed by dividing net income available to common stockholders by the weighted-average number of common shares outstanding, less unvested restricted stock for the period.  Diluted EPS is computed by dividing net income by the weighted-average number of common shares outstanding and dilutive potential common shares for the period.  Potential common shares include the weighted-average dilutive effects of outstanding stock options and unvested restricted stock using the treasury stock method.
	The following table sets forth the number of weighted-average shares used to compute basic and diluted EPS:
		Three Months Ended				Six Months Ended
		March 29,		March 30,		March 29,		March 30,
		2015		2014		2015		2014
		(in thousands, except per share data)
	Net income attributable to Tetra Tech	$	19,017	$	31,709	$	44,592	$	59,023
	Weighted-average common shares outstanding – basic	61,153		64,835		61,816		64,670
	Effect of dilutive stock options and unvested restricted stock	570		875		615		847
	Weighted-average common stock outstanding – diluted	61,723		65,710		62,431		65,517
	Earnings per share attributable to Tetra Tech:
	Basic	$	0.31	$	0.49	$	0.72	$	0.91
	Diluted	$	0.31	$	0.48	$	0.71	$	0.90
	For both three and six months ended March 29, 2015, 1.3 million options were excluded from the calculation of dilutive potential common shares, compared to 0.3 million and no options for the same periods last year.  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 during the period.  Therefore, their inclusion would have been anti-dilutive.

Income_Taxes

Income Taxes	6 Months Ended
	Mar. 29, 2015
Income Taxes
Income Taxes
	9.Income Taxes
	The effective tax rates for the first half of fiscal 2015 and 2014 were 29.6% and 30.3%, respectively.  During the first quarter of fiscal 2015, the Tax Increase Prevention Act of 2014 was signed into law.  This law retroactively extended the federal research and experimentation credits (“R&E credits”) for amounts incurred from January 1, 2014 through December 31, 2014.  Our income tax expense for the first half of fiscal 2015 includes a tax benefit of $1.2 million attributable to operating income during the last nine months of fiscal 2014, primarily related to the retroactive recognition of these tax credits.
	At March 29, 2015, approximately $56.7 million of undistributed earnings of our foreign subsidiaries, primarily in Canada, 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.  Determination of the amount of unrecognized deferred U.S. income tax liability is not practicable; however, the potential foreign tax credit associated with the deferred income would be available to partially reduce the resulting U.S. tax liabilities.
	We review the realizability of deferred tax assets on a quarterly basis by assessing the need for a valuation allowance.  As of March 29, 2015, we performed our assessment of net deferred tax assets.  Significant management judgment is required in determining the provision for income taxes and, in particular, any valuation allowance recorded against our deferred tax assets.  Applying the applicable accounting guidance requires an assessment of all available evidence, both positive and negative, regarding the realizability of the net deferred tax assets.  Based upon recent results, we concluded that a cumulative loss in recent years exists in certain foreign jurisdictions.  We have historically relied on the following factors in our assessment of the realizability of our net deferred tax assets:
		·	taxable income in prior carryback years as permitted under the tax law;
		·	future reversals of existing taxable temporary differences;
		·	consideration of available tax planning strategies and actions that could be implemented, if necessary; and
		·	estimates of future taxable income from our operations.
	We considered these factors in our estimate of the reversal pattern of deferred tax assets, using assumptions that we believe are reasonable and consistent with operating results.  However, as a result of projected cumulative pre-tax losses in these certain foreign jurisdictions for the 36 months ending September 27, 2015, we concluded that our estimates of future taxable income and certain tax planning strategies did not constitute sufficient positive evidence to assert that it is more likely than not that certain deferred tax assets would be realizable before expiration.  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 loss carry-forwards in foreign jurisdictions for which a valuation allowance of $7.4 million has been provided in prior years.

Reportable_Segments

Reportable Segments	6 Months Ended
	Mar. 29, 2015
Reportable Segments
Reportable Segments
	10.Reportable Segments
	Beginning in the first quarter of fiscal 2015, we reorganized our core operations into our WEI and RME reportable segments.  The results of the wind-down of our non-core construction activities are reported in the RCM reportable segment.  Prior year amounts for reportable segments have been revised to conform to the current-year presentation.
	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 and industrial clients.  The primary markets for WEI’s services include water management, environmental restoration, government consulting, and a broad range of civil infrastructure requirements 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 oil and gas, energy, mining, remediation, utilities, waste management, and international development.  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 supports engineering, procurement and construction management (“EPCM”) for full service implementation of commercial projects, especially for oil and gas, industrial, and mining customers.
	RCM:  We report the results of the wind-down of our non-core construction activities in the RCM reportable segment.  We plan to complete the remaining work performed in this segment primarily in fiscal 2015.
	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.
	The following tables set forth summarized financial information regarding our reportable segments:
	Reportable Segments
		Three Months Ended				Six Months Ended
		March 29,		March 30,		March 29,		March 30,
		2015		2014		2015		2014
		(in thousands)
	Revenue
	WEI	$	223,366	$	223,977	$	457,033	$	453,307
	RME	342,185		342,897		673,859		702,161
	RCM	18,151		40,282		52,581		122,364
	Elimination of inter-segment revenue	-18,939		-20,871		-37,654		-45,699
	Total revenue	$	564,763	$	586,285	$	1,145,819	$	1,232,133
	Operating Income (Loss)
	WEI	$	15,787	$	18,296	$	37,620	$	40,521
	RME	19,751		10,726		45,471		43,985
	RCM	5		730		-3,416		-3,401
	Corporate (1)	-5,145		16,434		-12,665		8,799
	Total operating income	$	30,398	$	46,186	$	67,010	$	89,904
	Depreciation
	WEI	$	1,189	$	1,362	$	2,422	$	2,777
	RME	3,665		3,708		7,344		7,870
	RCM	675		771		1,335		1,569
	Corporate (1)	400		737		1,692		1,491
	Total depreciation	$	5,929	$	6,578	$	12,793	$	13,707
	(1)   Includes amortization of intangibles, other costs, and other income not allocable to our reportable segments.
		March 29,		September 28,
		2015		2014
		(in thousands)
	Total Assets
	WEI	$	253,282	$	302,877
	RME	435,039		442,911
	RCM	91,418		100,996
	Corporate (1)	864,208		929,620
	Total assets	$	1,643,947	$	1,776,404
	(1)Corporate assets consist of intercompany eliminations and assets not allocated to our reportable segments including goodwill, intangible assets, deferred income taxes and certain other assets.
	Major Clients
	Other than the U.S. federal government, no single client accounted for more than 10% of our revenue.  All of our segments generated revenue from all client sectors.
	The following table represents our revenue by client sector:
		Three Months Ended				Six Months Ended
		March 29,		March 30,		March 29,		March 30,
		2015		2014		2015		2014
		(in thousands)
	Client Sector
	International (1)	$	173,680	$	181,570	$	320,741	$	345,504
	U.S. commercial	158,156		147,854		333,339		334,150
	U.S. federal government (2)	168,250		178,341		352,436		373,525
	U.S. state and local government	64,677		78,520		139,303		178,954
	Total	$	564,763	$	586,285	$	1,145,819	$	1,232,133
	(1)Includes revenue generated from foreign operations, primarily in Canada, and revenue generated from non-U.S. clients.
	(2)Includes revenue generated under U.S. federal government contracts performed outside the United States.

Fair_Value_Measurements

Fair Value Measurements	6 Months Ended
	Mar. 29, 2015
Fair Value Measurements
Fair Value Measurements
	11.Fair Value Measurements
	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 “Critical Accounting Policies and Estimates” in our Annual Report on Form 10-K for the fiscal year ended September 28, 2014).  The carrying value of our long-term debt approximated fair value at March 29, 2015 and September 28, 2014.  As of March 29, 2015, we had borrowings of $237.9 million outstanding under our amended credit agreement, which were used to fund our business acquisitions, working capital needs, and contingent earn-outs.

Joint_Ventures

Joint Ventures	6 Months Ended
	Mar. 29, 2015
Joint Ventures
Joint Ventures
	12.Joint Ventures
	Consolidated Joint Ventures
	The aggregate revenue from our consolidated joint ventures for the three and six months ended March 29, 2015 was $1.6 million and $3.8 million, respectively, compared to $3.5 million and $6.2 million for the same periods last year.  The assets and liabilities of these consolidated joint ventures were immaterial at March 29, 2015 and September 28, 2014.  These assets are restricted for use only by those joint ventures and are not available for our general operations.  Cash and cash equivalents maintained by the consolidated joint ventures at March 29, 2015 and September 28, 2014 were $1.3 million and $1.4 million, respectively.
	Unconsolidated Joint Ventures
	We account for our unconsolidated joint ventures using the equity method of accounting.  Under this method, we recognize our proportionate share of the net earnings of these joint ventures within “Other costs of revenue” in our condensed consolidated statements of income.  For the three and six months ended March 29, 2015, we reported $1.2 million and $1.8 million of equity in earnings of unconsolidated joint ventures, respectively, compared to $0.8 million and $1.5 million for the same periods last year.  Our maximum exposure to loss as a result of our investments in unconsolidated joint ventures is typically limited to the aggregate of the carrying value of the investment.  Future funding commitments for our unconsolidated joint ventures are immaterial.  The unconsolidated joint ventures are, individually and in the aggregate, immaterial to our condensed consolidated financial statements.
	The aggregate carrying values of the assets and liabilities of the unconsolidated joint ventures were $17.6 million and $15.4 million, respectively, at March 29, 2015, and $20.1 million and $18.0 million, respectively, at September 28, 2014.

Derivative_Financial_Instrumen

Derivative Financial Instruments	6 Months Ended
	Mar. 29, 2015
Derivative Financial Instruments
Derivative Financial Instruments
	13.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 condensed consolidated balance sheets at fair value (Level 2 measurement, as described in “Critical Accounting Policies and Estimates” in our Annual Report on Form 10-K for the fiscal year ended September 28, 2014).  We record changes in the fair value (i.e., gains or losses) of the derivatives that have been designated as accounting hedges in our condensed consolidated balance sheets as accumulated other comprehensive income (loss).
	In fiscal 2013, we entered into three interest rate swap agreements that we 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 the term loan facility.  At March 29, 2015, the effective portion of our interest rate swap agreements designated as cash flow hedges before tax effect was $1.8 million, all of which we expect to reclassify from accumulated other comprehensive income to interest expense within the next 12 months.
	As of March 29, 2015, the total notional principal amount of our outstanding interest rate swap agreements which expire in May 2018 was $197.3 million and the weighted average fixed interest rate was 1.32%.
	The fair values of our outstanding derivatives designated as hedging instruments are as follows:
		Balance Sheet Location	March 29,		September 28,
			2015		2014
			(in thousands)
	Interest rate swap agreements	Other current liabilities	$	2,034	$	45
	The impact of the effective portions of derivative instruments in cash flow hedging relationships on income and other comprehensive income from our foreign currency forward contracts and interest rate swap agreements was immaterial for the first six months of fiscal 2015 and the fiscal year ended September 28, 2014.  Additionally, there were no ineffective portions of derivative instruments.  Accordingly, no amounts were excluded from effectiveness testing for our foreign currency forward contracts and interest rate swap agreements.  We had no derivative instruments that were not designated as hedging instruments for fiscal 2014 and the first half of fiscal 2015.

Reclassifications_Out_of_Accum

Reclassifications Out of Accumulated Other Comprehensive Income (Loss)	6 Months Ended
	Mar. 29, 2015
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)
	14.Reclassifications Out of Accumulated Other Comprehensive Income (Loss)
	The accumulated balances and reporting period activities for the three and six months ended March 29, 2015 and September 28, 2014 related to reclassifications out of accumulated other comprehensive income (loss) are summarized as follows:
		Three Months Ended
		Foreign		Loss on		Accumulated
		Currency		Derivative		Other
		Translation		Instruments		Comprehensive
		Adjustments				Income (Loss)
		(in thousands)
	Balances at December 29, 2013	$	-19,756	$	343	$	-19,413
	Other comprehensive income (loss) before reclassifications	-15,650		262		-15,388
	Reclassification adjustment of prior derivative settlement, net of tax	–		-648		-648
	Net current-period other comprehensive loss	-15,650		-386		-16,036
	Balances at March 30, 2014	$	-35,406	$	-43	$	-35,449
	Balances at December 28, 2014	$	-67,654	$	67	$	-67,587
	Other comprehensive loss before reclassifications	-43,516		-938		-44,454
	Reclassification adjustment of prior derivative settlement, net of tax	–		-579		-579
	Net current-period other comprehensive loss	-43,516		-1,517		-45,033
	Balances at March 29, 2015	$	-111,170	$	-1,450	$	-112,620
		Six Months Ended
		Foreign		Loss on		Accumulated
		Currency		Derivative		Other
		Translation		Instruments		Comprehensive
		Adjustments				Income (Loss)
		(in thousands)
	Balances at September 29, 2013	$	2,340	$	-482	$	1,858
	Other comprehensive income (loss) before reclassifications	-37,746		1,570		-36,176
	Reclassification adjustment of prior derivative settlement, net of tax	–		-1,131		-1,131
	Net current-period other comprehensive income (loss)	-37,746		439		-37,307
	Balances at March 30, 2014	$	-35,406	$	-43	$	-35,449
	Balances at September 28, 2014	$	-43,085	$	547	$	-42,538
	Other comprehensive loss before reclassifications	-68,085		-828		-68,913
	Reclassification adjustment of prior derivative settlement, net of tax	–		-1,169		-1,169
	Net current-period other comprehensive loss	-68,085		-1,997		-70,082
	Balances at March 29, 2015	$	-111,170	$	-1,450	$	-112,620

Commitments_and_Contingencies

Commitments and Contingencies	6 Months Ended
	Mar. 29, 2015
Commitments and Contingencies
Commitments and Contingencies
	15.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.
	We acquired BPR Inc. (“BPR”), a Quebec-based engineering firm on October 4, 2010.  Subsequently, we have been informed of the following with respect to pre-acquisition activities at BPR:
	On April 17, 2012, authorities in the province of Quebec, Canada charged two former employees of BPR Triax, a subsidiary of BPR, and BPR Triax, under the Canadian Criminal Code with allegations of corruption.  Discovery procedures associated with the charges are currently ongoing, and the legal process is expected to continue into 2016.  We have conducted an internal investigation concerning this matter and, based on the results of our investigation, we believe these allegations are limited to activities at BPR Triax prior to our acquisition of BPR.  The financial impact to us of this matter is unknown at this time.
	On April 19, 2013, a class action proceeding was filed in Montreal in which BPR, BPR’s former president, and other Quebec-based engineering firms and individuals are named as defendants.  The plaintiff class includes all individuals and entities that have paid real estate or municipal taxes to the city of Montreal.  The allegations include participation in collusion to share contracts awarded by the City of Montreal, conspiracy to reduce competition and fix prices, payment of bribes to officials, making illegal political contributions, and bid rigging.  A class certification hearing was held in March 2014, and on May 7, 2014, the court dismissed the action.  On June 5, 2014, the plaintiff filed an appeal, and on November 3, 2014, the court dismissed this appeal.  The plaintiff filed an appeal with the Supreme Court of Canada, and on April 23, 2015, the court dismissed the application.  Accordingly, this matter is officially closed.

Recent_Accounting_Pronouncemen

Recent Accounting Pronouncements	6 Months Ended
	Mar. 29, 2015
Recent Accounting Pronouncements
Recent Accounting Pronouncements
	16.Recent Accounting Pronouncements
	In July 2013, the FASB issued an update on the financial statement presentation of unrecognized tax benefits.  We are required to present a liability related to an unrecognized tax benefit as a reduction of a deferred tax asset for a net operating loss carryforward, a similar tax loss or a tax credit carryforward if such settlement is required or expected in the event the uncertain tax position is disallowed.  This guidance became effective for us in the first quarter of fiscal 2015, and did not have a material impact on our consolidated financial statements.
	In April 2014, the FASB issued guidance that changes the threshold for reporting discontinued operations and adds new disclosures.  The new guidance defines a discontinued operation as a disposal of a component or group of components that is disposed of or is classified as held for sale and “represents a strategic shift that has (or will have) a major effect on our operations and financial results.”  For disposals of individually significant components that do not qualify as discontinued operations, we must disclose pre-tax earnings of the disposed component.  This guidance is effective for us prospectively for all disposals (or classifications as held for sale) of components of an entity that occur within annual periods beginning on or after December 15, 2014, and interim periods within those years.  Early adoption is permitted, but only for disposals (or classifications as held for sale) that have not been reported in financial statements previously issued or available for issuance.  We do not expect the adoption of this guidance to have a material impact on our consolidated financial statements.
	In May 2014, the FASB issued and 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 accounting standard is effective for us in the first quarter of fiscal year 2018.  Companies may use either a full retrospective or a modified retrospective approach to adopt this standard, and management is currently evaluating which transition approach to use.  In April 2015, the FASB proposed a deferral of the effective date of the new revenue standard by one year, subject to the FASB’s due process requirement.  We are currently in the process of assessing what impact this new standard may have on our condensed consolidated financial statements.
	In June 2014, the FASB issued updated guidance intended to eliminate the diversity in practice regarding share-based payment awards that include terms which provide for a performance target that affects vesting being achieved after the requisite service period.  The new standard requires that a performance target which affects vesting and could be achieved after the requisite service period be treated as a performance condition that affects vesting and should not be reflected in estimating the grant-date fair value.  The updated guidance is effective for interim and annual reporting periods beginning after December 15, 2015, with early adoption permitted.  We do not expect the adoption of this guidance to have an impact on our condensed consolidated financial statements.
	In August 2014, the FASB issued an amendment to the accounting guidance related to the evaluation of an entity to continue as a going concern.  The amendment established management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern in connection with preparing financial statements for each annual and interim reporting period.  The update also gives guidance to determine whether to disclose information about relevant conditions and events when there is substantial doubt about an entity’s ability to continue as a going concern.  This guidance is effective for us in the first quarter of fiscal 2017.  We do not expect the adoption of this guidance to have an impact on our condensed consolidated financial statements.
	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 is effective for us in the first quarter of fiscal 2017.  We do not expect the adoption of this guidance to have an impact on our condensed consolidated financial statements.
	In February 2015, the FASB issued updated guidance which changes the analysis that a reporting entity must perform to determine whether it should consolidate certain types of legal entities.  The updated guidance is effective for interim and annual reporting periods beginning after December 15, 2015, with early adoption permitted.  We do not expect the adoption of this guidance to have an impact on our condensed consolidated financial statements.
	In April 2015, the FASB issued updated guidance intended to simplify, and provide consistency to, the presentation of debt issuance costs.  The new standard requires that debt issuance costs be presented in the balance sheet as a direct deduction from the carrying amount of the debt liability, consistent with debt discounts.  The updated guidance is effective for interim and annual reporting periods beginning after December 15, 2015, with early adoption permitted.  We do not expect the adoption of this guidance to have an impact on our condensed consolidated financial statements.

Accounts_Receivable_Net_and_Re1

Accounts Receivable - Net and Revenue Recognition (Tables)	6 Months Ended
	Mar. 29, 2015
Accounts Receivable - Net and Revenue Recognition
Net accounts receivable and billings in excess of costs on uncompleted contracts
		March 29,		September 28,
		2015		2014
		(in thousands)
	Billed	$	314,993	$	351,693
	Unbilled	359,574		363,050
	Contract retentions	26,008		26,929
	Total accounts receivable – gross	700,575		741,672
	Allowance for doubtful accounts	-34,562		-39,780
	Total accounts receivable – net	$	666,013	$	701,892
	Billings in excess of costs on uncompleted contracts	$	95,270	$	103,343

Goodwill_and_Intangible_Assets1

Goodwill and Intangible Assets (Tables)	6 Months Ended
	Mar. 29, 2015
Goodwill and Intangible Assets
Summary of changes in the carrying value of goodwill
		WEI			RME			Total
		(in thousands)
	Balance at September 28, 2014	$	238,086		$	476,104		$	714,190
	Foreign exchange translation	-15,528			-27,265			-42,793
	Balance at March 29, 2015	$	222,558		$	448,839		$	671,397
Summary of acquired identifiable intangible assets with finite useful lives
		March 29, 2015								September 28, 2014
		Weighted-		Gross			Accumulated			Gross		Accumulated
		Average		Amount			Amortization			Amount		Amortization
		Remaining Life
		(in Years)
		($ in thousands)
	Non-compete agreements	1.5		$	933		$	-564		$	1,086	$	-524
	Client relations	3.4		113,716			-65,824			122,198		-61,117
	Backlog	–		1,070			-1,070			1,283		-1,072
	Technology and trade names	1.6		2,627			-1,826			2,917		-1,676
	Total			$	118,346		$	-69,284		$	127,484	$	-64,389
Estimated amortization expense for the succeeding five years and beyond
		Amount
		(in thousands)
	2015	$	8,842
	2016	15,616
	2017	13,727
	2018	6,038
	2019	2,832
	Beyond	2,007
	Total	$	49,062

Property_and_Equipment_Tables

Property and Equipment (Tables)	6 Months Ended
	Mar. 29, 2015
Property and Equipment
Schedule of components of property and equipment
		March 29,		September 28,
		2015		2014
		(in thousands)
	Land and buildings	$	3,648	$	4,029
	Equipment, furniture and fixtures	174,056		204,298
	Leasehold improvements	23,047		24,478
	Total property and equipment	200,751		232,805
	Accumulated depreciation	-135,644		-158,941
	Property and equipment, net	$	65,107	$	73,864

Earnings_Per_Share_EPS_Tables

Earnings Per Share ("EPS") (Tables)	6 Months Ended
	Mar. 29, 2015
Earnings Per Share ("EPS")
Schedule of number of weighted-average shares used to compute basic and diluted EPS
		Three Months Ended				Six Months Ended
		March 29,		March 30,		March 29,		March 30,
		2015		2014		2015		2014
		(in thousands, except per share data)
	Net income attributable to Tetra Tech	$	19,017	$	31,709	$	44,592	$	59,023
	Weighted-average common shares outstanding – basic	61,153		64,835		61,816		64,670
	Effect of dilutive stock options and unvested restricted stock	570		875		615		847
	Weighted-average common stock outstanding – diluted	61,723		65,710		62,431		65,517
	Earnings per share attributable to Tetra Tech:
	Basic	$	0.31	$	0.49	$	0.72	$	0.91
	Diluted	$	0.31	$	0.48	$	0.71	$	0.90

Reportable_Segments_Tables

Reportable Segments (Tables)	6 Months Ended
	Mar. 29, 2015
Reportable Segments
Summarized financial information of reportable segments
		Three Months Ended				Six Months Ended
		March 29,		March 30,		March 29,		March 30,
		2015		2014		2015		2014
		(in thousands)
	Revenue
	WEI	$	223,366	$	223,977	$	457,033	$	453,307
	RME	342,185		342,897		673,859		702,161
	RCM	18,151		40,282		52,581		122,364
	Elimination of inter-segment revenue	-18,939		-20,871		-37,654		-45,699
	Total revenue	$	564,763	$	586,285	$	1,145,819	$	1,232,133
	Operating Income (Loss)
	WEI	$	15,787	$	18,296	$	37,620	$	40,521
	RME	19,751		10,726		45,471		43,985
	RCM	5		730		-3,416		-3,401
	Corporate (1)	-5,145		16,434		-12,665		8,799
	Total operating income	$	30,398	$	46,186	$	67,010	$	89,904
	Depreciation
	WEI	$	1,189	$	1,362	$	2,422	$	2,777
	RME	3,665		3,708		7,344		7,870
	RCM	675		771		1,335		1,569
	Corporate (1)	400		737		1,692		1,491
	Total depreciation	$	5,929	$	6,578	$	12,793	$	13,707
	(1)   Includes amortization of intangibles, other costs, and other income not allocable to our reportable segments.
		March 29,		September 28,
		2015		2014
		(in thousands)
	Total Assets
	WEI	$	253,282	$	302,877
	RME	435,039		442,911
	RCM	91,418		100,996
	Corporate (1)	864,208		929,620
	Total assets	$	1,643,947	$	1,776,404
	(1)Corporate assets consist of intercompany eliminations and assets not allocated to our reportable segments including goodwill, intangible assets, deferred income taxes and certain other assets.
Summary of revenue by client sector
		Three Months Ended				Six Months Ended
		March 29,		March 30,		March 29,		March 30,
		2015		2014		2015		2014
		(in thousands)
	Client Sector
	International (1)	$	173,680	$	181,570	$	320,741	$	345,504
	U.S. commercial	158,156		147,854		333,339		334,150
	U.S. federal government (2)	168,250		178,341		352,436		373,525
	U.S. state and local government	64,677		78,520		139,303		178,954
	Total	$	564,763	$	586,285	$	1,145,819	$	1,232,133
	(1)Includes revenue generated from foreign operations, primarily in Canada, and revenue generated from non-U.S. clients.
	(2)Includes revenue generated under U.S. federal government contracts performed outside the United States.

Derivative_Financial_Instrumen1

Derivative Financial Instruments (Tables)	6 Months Ended
	Mar. 29, 2015
Derivative Financial Instruments
Schedule of fair values of the entity's outstanding derivatives designated as hedging instruments
		Balance Sheet Location	March 29,		September 28,
			2015		2014
			(in thousands)
	Interest rate swap agreements	Other current liabilities	$	2,034	$	45

Reclassifications_Out_of_Accum1

Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Mar. 29, 2015
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)
Summary of reclassifications out of accumulated other comprehensive income (loss)
		Three Months Ended
		Foreign		Loss on		Accumulated
		Currency		Derivative		Other
		Translation		Instruments		Comprehensive
		Adjustments				Income (Loss)
		(in thousands)
	Balances at December 29, 2013	$	-19,756	$	343	$	-19,413
	Other comprehensive income (loss) before reclassifications	-15,650		262		-15,388
	Reclassification adjustment of prior derivative settlement, net of tax	–		-648		-648
	Net current-period other comprehensive loss	-15,650		-386		-16,036
	Balances at March 30, 2014	$	-35,406	$	-43	$	-35,449
	Balances at December 28, 2014	$	-67,654	$	67	$	-67,587
	Other comprehensive loss before reclassifications	-43,516		-938		-44,454
	Reclassification adjustment of prior derivative settlement, net of tax	–		-579		-579
	Net current-period other comprehensive loss	-43,516		-1,517		-45,033
	Balances at March 29, 2015	$	-111,170	$	-1,450	$	-112,620
		Six Months Ended
		Foreign		Loss on		Accumulated
		Currency		Derivative		Other
		Translation		Instruments		Comprehensive
		Adjustments				Income (Loss)
		(in thousands)
	Balances at September 29, 2013	$	2,340	$	-482	$	1,858
	Other comprehensive income (loss) before reclassifications	-37,746		1,570		-36,176
	Reclassification adjustment of prior derivative settlement, net of tax	–		-1,131		-1,131
	Net current-period other comprehensive income (loss)	-37,746		439		-37,307
	Balances at March 30, 2014	$	-35,406	$	-43	$	-35,449
	Balances at September 28, 2014	$	-43,085	$	547	$	-42,538
	Other comprehensive loss before reclassifications	-68,085		-828		-68,913
	Reclassification adjustment of prior derivative settlement, net of tax	–		-1,169		-1,169
	Net current-period other comprehensive loss	-68,085		-1,997		-70,082
	Balances at March 29, 2015	$	-111,170	$	-1,450	$	-112,620

Accounts_Receivable_Net_and_Re2

Accounts Receivable - Net and Revenue Recognition (Details) (USD $)	3 Months Ended			6 Months Ended
	Mar. 29, 2015	Sep. 28, 2014	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014
Accounts Receivable - Net and Revenue Recognition
Billed	$314,993,000	$351,693,000		$314,993,000
Unbilled	359,574,000	363,050,000		359,574,000
Contract retentions	26,008,000	26,929,000		26,008,000
Total accounts receivable - gross	700,575,000	741,672,000		700,575,000
Allowance for doubtful accounts	-34,562,000	-39,780,000		-34,562,000
Total accounts receivable - net	666,013,000	701,892,000		666,013,000
Billings in excess of costs on uncompleted contracts	95,270,000	103,343,000		95,270,000
Period for billing and collecting unbilled receivables				12 months
Period for earning majority of billings in excess of costs				12 months
Total accounts receivable related to claims and requests for equitable adjustment on contracts	80,000,000	79,000,000		80,000,000
Reduction in the revenue related to the evaluation of claim amounts	3,000,000
Decrease in operating income related to the evaluation of claim amounts	3,000,000
Net gains on settlement of claims			3,400,000	200,000	3,400,000
Billed accounts receivable related to U.S. federal government contracts	59,300,000	57,400,000		59,300,000
U.S. federal government unbilled receivables	68,200,000	73,200,000		68,200,000
Threshold percentage for disclosure of accounts receivable from a single client		10.00%		10.00%
Revenue Recognition and Contract Costs
Net unfavorable operating income adjustments	3,500,000		5,300,000	5,900,000	5,300,000
Liability for anticipated losses	13,600,000	18,600,000		13,600,000
Estimated cost to complete the related contracts	$83,900,000			$83,900,000
Accounts Receivable
Account receivable major customer
Number of clients exceeding threshold		0		0

Mergers_and_Acquisitions_Detai

Mergers and Acquisitions (Details)	3 Months Ended	6 Months Ended				3 Months Ended				6 Months Ended	3 Months Ended				6 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014	Mar. 29, 2015	Mar. 29, 2015	Mar. 29, 2015	Mar. 29, 2015	Sep. 28, 2014	Dec. 29, 2013	Mar. 29, 2015	Sep. 28, 2014	Mar. 30, 2014	Dec. 29, 2013	Mar. 31, 2013	Mar. 30, 2014	Sep. 28, 2014
	USD ($)	USD ($)	USD ($)	Maximum	Minimum	Caber	Caber	Caber	Caber	Caber	Parkland	Parkland	Parkland	Parkland	Parkland	Parkland
		item				USD ($)	CAD	USD ($)	CAD	USD ($)	USD ($)	USD ($)	USD ($)	CAD	USD ($)	USD ($)
Business acquisition
Number of acquisitions		0
Contingent earn-out liability		$0				$0				$0	$0	$0	$0		$0	$0
Aggregate maximum of contingent consideration		20.6							8
Earn-out period for operating income projection				3 years	2 years				2 years					3 years
Decreases (increase) in contingent earn-out liabilities						3.1		-1		3.1		21.3			26
Net decrease in contingent earn-out liabilities																44.6
Gains on fair value adjustment in operating income	5.6					3.1				3.1		21.3			26
Net gains on fair value adjustments in operating income																44.6
Earn-out paid to former owners		3.2	10.6			3.2	4
Potential earn-out to be paid each year									4
Potential maximum earn-out to be paid									4					56
Potential earn-out to be paid in the first year														12
Potential earn-out to be paid in the second year														22
Potential earn-out to be paid in the third year														22
Minimum operating income threshold to earn contingent consideration during year one									4					34.7
Minimum operating income threshold to earn contingent consideration during year two									4.6					38.2
Minimum operating income threshold to earn contingent consideration during year three														41.9
Operating income to earn maximum consideration during the first year									4.4					42.5
Operating income to earn maximum consideration during the second year									5.1					46.4
Operating income to earn maximum consideration during the third year														50.6
Initial fair value of the contingent consideration									6.5					46.8
Estimated potential earn-out (as a percent)									81.00%					84.00%
Gain (loss) on change in contingent consideration						3.1		-1			19.9	19.1	5.6		24.7
Profit previously recognized on project												5.3
Earn-outs paid to former owners reported as cash used in financing activities		3.2	9.3
Earn-outs paid to former owners reported as cash used in operating activities			$1.30

Goodwill_and_Intangible_Assets2

Goodwill and Intangible Assets (Details) (USD $)	0 Months Ended		6 Months Ended
	Sep. 29, 2014	Jun. 30, 2014	Mar. 29, 2015	Sep. 28, 2014
Goodwill information
Goodwill			$671,397,000
Goodwill
Balance at beginning of the period	714,190,000		714,190,000
Foreign exchange translation			-42,793,000
Balance at end of the period			671,397,000
Impairment of goodwill	0	0
WEI
Goodwill information
Goodwill			222,558,000
Goodwill
Balance at beginning of the period	238,086,000		238,086,000
Foreign exchange translation			-15,528,000
Balance at end of the period			222,558,000
Gross amounts of goodwill			253,700,000	269,200,000
Accumulated impairment			31,100,000	31,100,000
RME
Goodwill information
Goodwill			448,839,000
Goodwill
Balance at beginning of the period	476,104,000		476,104,000
Foreign exchange translation			-27,265,000
Balance at end of the period			448,839,000
Gross amounts of goodwill			475,200,000	502,500,000
Accumulated impairment			$26,400,000	$26,400,000

Goodwill_and_Intangible_Assets3

Goodwill and Intangible Assets (Details 2) (USD $)	6 Months Ended
	Mar. 29, 2015	Sep. 28, 2014
Goodwill	671,397,000	$714,190,000
RME
Goodwill	448,839,000	476,104,000
RME | GMP
Fair value of business	102,800,000
Carrying value of business	91,800,000
Goodwill	61,400,000
RME | GMP | US treasury bonds
Impairment of goodwill
Maturity of investments whose yield is considered in determination of impairment	20 years
Goodwill. | RME | GMP
Discounted cash flow rate (as a percent)	14.00%
Revenue multiple	0.7
Impairment of goodwill
Significant contraction in mining activity period	2 years
Goodwill. | RME | GMP | Minimum
Annual revenue growth rate (as a percent)	3.00%
Impairment of goodwill
Decline in future revenue leading to goodwill impairment (as a percent)	20.00%
Decline in future market prices of similar businesses leading to goodwill impairment (as a percent)	15.00%
Discounted cash flow rate leading to impairment of goodwill (as a percent)	15.50%
Goodwill. | RME | GMP | Maximum
Annual revenue growth rate (as a percent)	5.00%
Income approach
Weighted rate used in fair value of goodwill (as a percent)	70.00%
Discounted cash flow and market approach
Weighted rate used in fair value of goodwill (as a percent)	30.00%

Goodwill_and_Intangible_Assets4

Goodwill and Intangible Assets (Details 3) (USD $)	3 Months Ended		6 Months Ended
	Mar. 29, 2015	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014	Sep. 28, 2014
Finite-lived intangible assets
Gross Amount	$118,346,000		$118,346,000		$127,484,000
Accumulated Amortization	-69,284,000		-69,284,000		-64,389,000
Foreign currency translation adjustments			3,300,000
Amortization expense for identifiable intangible assets	4,800,000	6,700,000	10,800,000	15,300,000
Estimated amortization expense
2015	8,842,000		8,842,000
2016	15,616,000		15,616,000
2017	13,727,000		13,727,000
2018	6,038,000		6,038,000
2019	2,832,000		2,832,000
Beyond	2,007,000		2,007,000
Total	49,062,000		49,062,000
Non-compete agreements
Finite-lived intangible assets
Weighted-Average Remaining Life			1 year 6 months
Gross Amount	933,000		933,000		1,086,000
Accumulated Amortization	-564,000		-564,000		-524,000
Client relations
Finite-lived intangible assets
Weighted-Average Remaining Life			3 years 4 months 24 days
Gross Amount	113,716,000		113,716,000		122,198,000
Accumulated Amortization	-65,824,000		-65,824,000		-61,117,000
Backlog
Finite-lived intangible assets
Gross Amount	1,070,000		1,070,000		1,283,000
Accumulated Amortization	-1,070,000		-1,070,000		-1,072,000
Technology and trade names
Finite-lived intangible assets
Weighted-Average Remaining Life			1 year 7 months 6 days
Gross Amount	2,627,000		2,627,000		2,917,000
Accumulated Amortization	($1,826,000)		($1,826,000)		($1,676,000)

Property_and_Equipment_Details

Property and Equipment (Details) (USD $)	3 Months Ended		6 Months Ended
	Mar. 29, 2015	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014	Sep. 28, 2014
Property and Equipment
Property and equipment at cost, gross	$200,751,000		$200,751,000		$232,805,000
Accumulated depreciation	-135,644,000		-135,644,000		-158,941,000
Property and equipment, net	65,107,000		65,107,000		73,864,000
Depreciation expense related to property and equipment, including assets under capital leases	5,929,000	6,578,000	12,793,000	13,707,000
Carrying value of property	3,600,000		3,600,000
Proceeds from sale of property and equipment			9,824,000	2,957,000
(Gain) loss on disposal of property and equipment			-6,175,000	717,000
Land and buildings
Property and Equipment
Property and equipment at cost, gross	3,648,000		3,648,000		4,029,000
Equipment, furniture and fixtures
Property and Equipment
Property and equipment at cost, gross	174,056,000		174,056,000		204,298,000
Leasehold improvements
Property and Equipment
Property and equipment at cost, gross	$23,047,000		$23,047,000		$24,478,000

Stock_Repurchase_and_Dividends1

Stock Repurchase and Dividends (Details) (USD $)	0 Months Ended		6 Months Ended	16 Months Ended	0 Months Ended
Share data in Millions, except Per Share data, unless otherwise specified	Jan. 26, 2015	Nov. 10, 2014	Mar. 29, 2015	Sep. 28, 2014	Apr. 27, 2015	Jun. 30, 2013
Maximum repurchase amount under stock repurchase program		$200,000,000				$100,000,000
Shares repurchased through open market purchases			2.7	3.9
Average price of shares repurchased (in dollars per share)			$25.11	$25.59
Cost of shares repurchased			68,700,000	100,000,000
Payment of ordinary dividends			$8,630,000
Quarterly cash dividend declared (in dollars per share)	$0.07	$0.07
Period of stock repurchase program		2 years
Subsequent Event
Quarterly cash dividend declared (in dollars per share)					$0.08

Stockholders_Equity_and_Stock_1

Stockholders' Equity and Stock Compensation Plans (Details) (USD $)	3 Months Ended		6 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 29, 2015	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014
Stockholders' Equity and Stock Compensation Plans
Stock-based compensation expense	$2.60	$3.20	$5.40	$5.50
Options granted (in shares)			266,420
Restricted stock award
Exercise price of stock options granted (in dollars per share)			$27.26
Weighted-average fair value of stock options granted (in dollars per share)			$8.20
Executive officers and employees
Restricted stock award
Vesting period			4 years
Non-employee director
Restricted stock award
Vesting period			1 year
Performance-based restricted stock
Restricted stock award
Percentage of shares that ultimately vest depending on fiscal year earnings per share growth rates			50.00%
Percentage of shares that ultimately vest depending on fiscal year shareholder vesting period			50.00%
Performance-based restricted stock | Non-employee directors and executive officers
Restricted stock award
Granted (in shares)			155,265
Granted, fair value (in dollars per share)			$27.26
Vesting period			3 years
Time-based restricted stock | Non-employee directors, executive officers and employees
Restricted stock award
Granted (in shares)			239,747
Granted, fair value (in dollars per share)			$27.26

Earnings_Per_Share_EPS_Details

Earnings Per Share (''EPS'') (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 29, 2015	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014
Number of weighted-average shares used to compute basic and diluted EPS:
Net income attributable to Tetra Tech	$19,017	$31,709	$44,592	$59,023
Weighted-average common shares outstanding - basic	61,153,000	64,835,000	61,816,000	64,670,000
Effect of diluted stock options and unvested restricted stock	570,000	875,000	615,000	847,000
Weighted-average common stock outstanding - diluted	61,723,000	65,710,000	62,431,000	65,517,000
Earnings per share attributable to Tetra Tech:
Basic	$0.31	$0.49	$0.72	$0.91
Diluted	$0.31	$0.48	$0.71	$0.90
Stock options
Antidilutive securities
Securities excluded from the calculation of dilutive potential common shares	1,300,000	300,000	1,300,000	0

Income_Taxes_Details

Income Taxes (Details) (USD $)	6 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Mar. 29, 2015	Mar. 30, 2014	Sep. 27, 2015
Income Taxes
Effective tax rate (as a percent)	29.60%	30.30%
Undistributed earnings of foreign subsidiaries	$56.70
Loss carry-forwards in foreign jurisdictions, valuation allowance	7.4
Represents the period of projected cumulative pre-tax losses in certain foreign jurisdictions			36 months
R&E credits	$1.20

Reportable_Segments_Details

Reportable Segments (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 29, 2015	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014	Sep. 28, 2014
Financial information concerning reportable segments
Revenue	$564,763	$586,285	$1,145,819	$1,232,133
Operating income (loss)	30,398	46,186	67,010	89,904
Depreciation	5,929	6,578	12,793	13,707
Total assets	1,643,947		1,643,947		1,776,404
Inter-segment elimination
Financial information concerning reportable segments
Revenue	-18,939	-20,871	-37,654	-45,699
Corporate
Financial information concerning reportable segments
Operating income (loss)	-5,145	16,434	-12,665	8,799
Depreciation	400	737	1,692	1,491
Corporate
Financial information concerning reportable segments
Total assets	864,208		864,208		929,620
WEI | Operating segment
Financial information concerning reportable segments
Revenue	223,366	223,977	457,033	453,307
Operating income (loss)	15,787	18,296	37,620	40,521
Depreciation	1,189	1,362	2,422	2,777
Total assets	253,282		253,282		302,877
RME | Operating segment
Financial information concerning reportable segments
Revenue	342,185	342,897	673,859	702,161
Operating income (loss)	19,751	10,726	45,471	43,985
Depreciation	3,665	3,708	7,344	7,870
Total assets	435,039		435,039		442,911
RCM | Operating segment
Financial information concerning reportable segments
Revenue	18,151	40,282	52,581	122,364
Operating income (loss)	5	730	-3,416	-3,401
Depreciation	675	771	1,335	1,569
Total assets	$91,418		$91,418		$100,996

Reportable_Segments_Details_2

Reportable Segments (Details 2) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 29, 2015	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014
Revenue by client sector
Threshold percentage for disclosure of revenue from a single client			10.00%
Revenue	$564,763	$586,285	$1,145,819	$1,232,133
Revenue
Revenue by client sector
Number of clients exceeding threshold			0
International
Revenue by client sector
Revenue	173,680	181,570	320,741	345,504
U.S. commercial
Revenue by client sector
Revenue	158,156	147,854	333,339	334,150
U.S. federal government
Revenue by client sector
Revenue	168,250	178,341	352,436	373,525
U.S. state and local government
Revenue by client sector
Revenue	$64,677	$78,520	$139,303	$178,954

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Mar. 29, 2015
In Millions, unless otherwise specified
Fair Value Measurements
Outstanding borrowings under the amended credit agreement	$237.90

Joint_Ventures_Details

Joint Ventures (Details) (USD $)	3 Months Ended		6 Months Ended
	Mar. 29, 2015	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014	Sep. 28, 2014
Aggregate revenue of consolidated joint ventures	$564,763,000	$586,285,000	$1,145,819,000	$1,232,133,000
Unconsolidated Joint Ventures
Equity in earnings from unconsolidated joint ventures	1,200,000	800,000	1,842,000	1,492,000
Carrying value of assets of unconsolidated joint ventures	17,600,000		17,600,000		20,100,000
Carrying value of liabilities of unconsolidated joint ventures	15,400,000		15,400,000		18,000,000
Consolidated Joint Ventures
Aggregate revenue of consolidated joint ventures	1,600,000	3,500,000	3,800,000	6,200,000
Cash and cash equivalents of consolidated joint ventures	$1,300,000		$1,300,000		$1,400,000

Derivative_Financial_Instrumen2

Derivative Financial Instruments (Details) (USD $)	6 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 29, 2015	Sep. 28, 2014	Dec. 29, 2013	Sep. 29, 2013
			item	item
Derivative financial instruments
Notional Amount	$197.30
Weighted average fixed rate	1.32%
Not designated as hedging instruments
Derivative financial instruments
Number of derivative instruments	0	0
Interest rate swap agreements | Derivatives designated as hedging instruments
Derivative financial instruments
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			2	3
Amount of effective portion of derivatives before tax effect	$1.80
Period of reclassification from accumulated other comprehensive income to interest expense	12 months

Derivative_Financial_Instrumen3

Derivative Financial Instruments (Details 2) (Interest rate swap agreements, Derivatives designated as hedging instruments, Designated as cash flow hedges, Other current liabilities, USD $)	Mar. 29, 2015	Sep. 28, 2014
In Thousands, unless otherwise specified
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	$2,034	$45

Reclassifications_Out_of_Accum2

Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 29, 2015	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014	Sep. 28, 2014
Reclassifications out of accumulated other comprehensive income (loss)
Balances at the beginning of the period					($42,538)
Balances at the end of the period	-112,620		-112,620		-42,538
Foreign Currency Translation Adjustments
Reclassifications out of accumulated other comprehensive income (loss)
Balances at the beginning of the period	-67,654	-19,756	-43,085	2,340
Other comprehensive income (loss) before reclassifications	-43,516	-15,650	-68,085	-37,746
Net current-period other comprehensive income (loss)	-43,516	-15,650	-68,085	-37,746
Balances at the end of the period	-111,170	-35,406	-111,170	-35,406
Loss on Derivative Instruments
Reclassifications out of accumulated other comprehensive income (loss)
Balances at the beginning of the period	67	343	547	-482
Other comprehensive income (loss) before reclassifications	-938	262	-828	1,570
Net current-period other comprehensive income (loss)	-1,517	-386	-1,997	439
Balances at the end of the period	-1,450	-43	-1,450	-43
Loss on Derivative Instruments | Foreign exchange contracts
Reclassifications out of accumulated other comprehensive income (loss)
Reclassification adjustment of prior derivative settlement, net of tax	-579	-648	-1,169	-1,131
Accumulated Other Comprehensive Income
Reclassifications out of accumulated other comprehensive income (loss)
Balances at the beginning of the period	-67,587	-19,413	-42,538	1,858
Other comprehensive income (loss) before reclassifications	-44,454	-15,388	-68,913	-36,176
Net current-period other comprehensive income (loss)	-45,033	-16,036	-70,082	-37,307
Balances at the end of the period	-112,620	-35,449	-112,620	-35,449
Accumulated Other Comprehensive Income | Foreign exchange contracts
Reclassifications out of accumulated other comprehensive income (loss)
Reclassification adjustment of prior derivative settlement, net of tax	($579)	($648)	($1,169)	($1,131)

Commitments_and_Contingencies_

Commitments and Contingencies (Details) (BPR Triax)	Apr. 17, 2012
	item
BPR Triax
Loss contingencies
Number of former employees of BPR Triax charged with allegations of corruption	2