Tetra Tech (TTEK) 10-Q 2 May 14 2014 Q2 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	6 Months Ended
	Mar. 30, 2014	Apr. 28, 2014
Document and Entity Information	'	'
Entity Registrant Name	'TETRA TECH INC	'
Entity Central Index Key	'0000831641	'
Document Type	'10-Q	'
Document Period End Date	30-Mar-14	'
Amendment Flag	'false	'
Current Fiscal Year End Date	'--09-28	'
Entity Current Reporting Status	'Yes	'
Entity Filer Category	'Large Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	64,957,358
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q2	'

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Mar. 30, 2014	Sep. 29, 2013
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$167,225	$129,305
Accounts receivable - net	656,481	660,847
Prepaid expenses and other current assets	52,325	61,446
Income taxes receivable	13,727	20,044
Total current assets	889,758	871,642
Property and equipment - net	80,352	88,026
Investments in and advances to unconsolidated joint ventures	2,494	2,198
Goodwill	709,502	722,792
Intangible assets - net	70,983	86,929
Other long-term assets	23,943	27,505
Total assets	1,777,032	1,799,092
Current liabilities:	'	'
Accounts payable	153,597	142,813
Accrued compensation	93,511	114,810
Billings in excess of costs on uncompleted contracts	85,970	79,507
Deferred income taxes	19,722	18,170
Current portion of long-term debt	8,532	4,311
Estimated contingent earn-out liabilities	27,265	23,281
Other current liabilities	71,430	100,241
Total current liabilities	460,027	483,133
Deferred income taxes	27,237	30,525
Long-term debt	198,219	203,438
Long-term estimated contingent earn-out liabilities	21,823	58,508
Other long-term liabilities	27,803	24,685
Commitments and contingencies	'	'
Equity:	'	'
Preferred stock - Authorized, 2,000 shares of $0.01 par value; no shares issued and outstanding at March 30, 2014, and September 29, 2013	'	'
Common stock - Authorized, 150,000 shares of $0.01 par value; issued and outstanding, 65,068 and 64,134 shares at March 30, 2014, and September 29, 2013, respectively	650	641
Additional paid-in capital	464,354	443,099
Accumulated other comprehensive income (loss)	-35,449	1,858
Retained earnings	611,188	552,165
Tetra Tech stockholders' equity	1,040,743	997,763
Noncontrolling interests	1,180	1,040
Total equity	1,041,923	998,803
Total liabilities and equity	$1,777,032	$1,799,092

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 30, 2014	Sep. 29, 2013
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	65,068	64,134
Common stock, shares outstanding	65,068	64,134

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. 30, 2014	Mar. 31, 2013	Mar. 30, 2014	Mar. 31, 2013
Condensed Consolidated Statements of Income	'	'	'	'
Revenue	$586,285	$641,999	$1,232,133	$1,300,544
Subcontractor costs	-130,300	-121,052	-293,158	-282,399
Other costs of revenue	-386,913	-435,827	-783,442	-844,822
Selling, general and administrative expenses	-44,229	-48,409	-91,602	-94,793
Contingent consideration - fair value adjustments	21,343	956	25,973	946
Operating income	46,186	37,667	89,904	79,476
Interest expense	-2,496	-2,136	-4,919	-3,320
Income before income tax expense	43,690	35,531	84,985	76,156
Income tax expense	-11,781	-10,659	-25,749	-24,888
Net income including noncontrolling interests	31,909	24,872	59,236	51,268
Net income attributable to noncontrolling interests	-200	-52	-213	-225
Net income attributable to Tetra Tech	$31,709	$24,820	$59,023	$51,043
Earnings per share attributable to Tetra Tech:	'	'	'	'
Basic (in dollars per share)	$0.49	$0.38	$0.91	$0.79
Diluted (in dollars per share)	$0.48	$0.38	$0.90	$0.78
Weighted-average common shares outstanding:	'	'	'	'
Basic (in shares)	64,835	64,551	64,670	64,376
Diluted (in shares)	65,710	65,472	65,517	65,208

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 30, 2014	Mar. 31, 2013	Mar. 30, 2014	Mar. 31, 2013
Condensed Consolidated Statements of Comprehensive Income	'	'	'	'
Net income including noncontrolling interests	$31,909	$24,872	$59,236	$51,268
Other comprehensive income (loss):	'	'	'	'
Foreign currency translation adjustments, net of tax	-15,684	-12,154	-37,819	-17,767
(Loss) gain on cash flow hedge valuations, net of tax	-386	-28	439	93
Other comprehensive loss	-16,070	-12,182	-37,380	-17,674
Comprehensive income including noncontrolling interests	15,839	12,690	21,856	33,594
Net income attributable to noncontrolling interests	-200	-52	-213	-225
Foreign currency translation adjustments, net of tax	34	20	73	33
Comprehensive income attributable to noncontrolling interests	-166	-32	-140	-192
Comprehensive income attributable to Tetra Tech	$15,673	$12,658	$21,716	$33,402

Condensed_Consolidated_Stateme2

Condensed Consolidated Statements of Cash Flows (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Mar. 30, 2014	Mar. 31, 2013
Cash flows from operating activities:	'	'
Net income including noncontrolling interests	$59,236	$51,268
Adjustments to reconcile net income to net cash from operating activities:	'	'
Depreciation and amortization	29,414	29,322
Loss on settlement of foreign currency forward contract	'	270
Equity in earnings of unconsolidated joint ventures	-1,492	-1,929
Distributions of earnings from unconsolidated joint ventures	1,064	1,549
Stock-based compensation	5,537	4,840
Excess tax benefits from stock-based compensation	-677	-866
Deferred income taxes	-2,658	4,880
Provision for doubtful accounts	3,634	2,164
Fair value adjustments to contingent consideration	-25,973	-946
Loss (gain) on disposal of property and equipment	717	-237
Changes in operating assets and liabilities, net of effects of business acquisitions:	'	'
Accounts receivable	5,550	75,183
Prepaid expenses and other assets	-4,101	-4,139
Accounts payable	9,517	-31,180
Accrued compensation	-21,403	-33,220
Billings in excess of costs on uncompleted contracts	6,460	-15,732
Other liabilities	-15,831	-6,208
Income taxes receivable/payable	7,212	-13,001
Net cash provided by operating activities	56,206	62,018
Cash flows from investing activities:	'	'
Capital expenditures	-11,699	-13,634
Payments for business acquisitions, net of cash acquired	-10,286	-168,092
Payment in settlement of foreign currency forward contract	'	-4,177
Receipt in settlement of foreign currency forward contract	'	3,907
Changes in restricted cash	'	470
Payment received on note for sale of operation	3,900	'
Proceeds from sale of property and equipment	2,957	962
Net cash used in investing activities	-15,128	-180,564
Cash flows from financing activities:	'	'
Payments on long-term debt	-459	-113,978
Proceeds from borrowings	'	296,098
Payments of earn-out liabilities	-9,337	-24,015
Net change in overdrafts	-915	291
Excess tax benefits from stock-based compensation	677	866
Repurchases of common stock	-6,612	'
Net proceeds from issuance of common stock	17,529	14,561
Net cash provided by financing activities	883	173,823
Effect of foreign exchange rate changes on cash	-4,041	-550
Net increase in cash and cash equivalents	37,920	54,727
Cash and cash equivalents at beginning of period	129,305	104,848
Cash and cash equivalents at end of period	167,225	159,575
Cash paid during the period for:	'	'
Interest	4,404	2,494
Income taxes, net of refunds received	$19,973	$31,531

Basis_of_Presentation

Basis of Presentation	6 Months Ended
	Mar. 30, 2014
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 29, 2013.
	These financial statements reflect all normal recurring adjustments that are considered necessary for the 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.  Certain immaterial reclassifications were made to the prior year to conform to current year presentation.

Accounts_Receivable_Net_and_Re

Accounts Receivable - Net and Revenue Recognition	6 Months Ended
	Mar. 30, 2014
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 30,		September 29,
		2014		2013
		(in thousands)
	Billed	$	338,377	$	375,149
	Unbilled	339,638		306,969
	Contract retentions	23,469		23,353
	Total accounts receivable – gross	701,484		705,471
	Allowance for doubtful accounts	-45,003		-44,624
	Total accounts receivable – net	$	656,481	$	660,847
	Billings in excess of costs on uncompleted contracts	$	85,970	$	79,507
	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 30, 2014 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 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 30, 2014 and September 29, 2013 include approximately $61 million and $41 million, respectively, related to claims, including requests for equitable adjustment, on contracts that provide for price redetermination, primarily with U.S. federal government agencies.  The increase from the end of fiscal 2013 primarily relates to the impact of cost overruns on an oil and gas project in Western Canada during the second quarter of fiscal 2014, primarily due to changes in scope that are currently in negotiation with the client.  As a result, we revised our estimate of the total costs to complete the project and recorded a charge of $5.3 million in the second quarter of fiscal 2014 to reverse profit recognized in prior periods.  As of March 30, 2014, this project was approximately 90% complete, with remaining estimated costs to complete of approximately $13 million.  In addition, during the second quarter of fiscal 2014, we recorded accounts receivable and revenue of approximately $10 million for this project based upon the portion of change orders that we believe have a technical and legal basis for recovery and are probable of collection. If the actual costs to complete the project exceed our estimates, or we are unable to fully collect the accounts receivable, we could incur further losses.  However, we intend to pursue all options to collect the entire amount of the change orders, which is expected to exceed the revenue recognized on the project.  If we are successful, we could recognize gains on recovery in future periods in our RCM segment.  In addition to new claims, we also regularly evaluate all claim amounts recorded as of the beginning of each period, 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 reliably estimated.  As a result of this assessment, we recognized revenue and an increase to operating income of $3.4 million and $1.1 million for the six months ended March 30, 2014 and March 31, 2013, respectively.
	Billed accounts receivable related to U.S. federal government contracts were $68.9 million and $50.5 million at March 30, 2014 and September 29, 2013, respectively.  U.S. federal government unbilled receivables, net of progress payments, were $69.9 million and $79.3 million at March 30, 2014 and September 29, 2013, respectively.  Other than the U.S. federal government, no single client accounted for more than 10% of our accounts receivable at March 30, 2014 and September 29, 2013.
	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. Revenue and cost estimates for each significant contract are reviewed and reassessed quarterly.  Changes in those estimates could result in recognition of cumulative catch-up adjustments to the contract’s inception-to-date revenue, costs and profit in the period in which such changes are made.  As a result, we recognized the net unfavorable operating income adjustment of $5.3 million previously described for the three and six months ended March 30, 2014.  No material operating income adjustments were recognized during the three and six months ended March 31, 2013.  Changes in revenue and cost estimates could also result in a projected loss that would be recorded immediately in earnings.  As of March 30, 2014 and September 29, 2013, we recorded a liability for anticipated losses of $9.2 million and $13.3 million, respectively.  The estimated cost to complete the related contracts as of March 30, 2014 was $41.1 million.  Loss contracts had an immaterial impact on our consolidated results for the three and six months ended March 30, 2014 and March 31, 2013.

Mergers_and_Acquisitions

Mergers and Acquisitions	6 Months Ended
	Mar. 30, 2014
Mergers and Acquisitions	'
Mergers and Acquisitions	'
	3.                                      Mergers and Acquisitions
	In the second quarter of fiscal 2013, we acquired American Environmental Group, Ltd. (“AEG”), headquartered in Richfield, Ohio.  AEG provides environmental, design, construction and maintenance services primarily to solid and hazardous waste, environmental, energy and utility clients.  Also in the second quarter of fiscal 2013, we acquired Parkland Pipeline Contractors Ltd., Parkland Pipeline Equipment Ltd., Park L Projects Ltd. and Parkland Projects Ltd. (collectively, “Parkland”), headquartered in Alberta, Canada.  Parkland serves the oil and gas industry in Western Canada, and specializes in the technical support, engineering support and construction of pipelines and oilfield facilities.  AEG and Parkland are both included in our Remediation and Construction Management (“RCM”) segment.  We also made other acquisitions that enhanced our service offerings and expanded our geographic presence in our Engineering and Consulting Services (“ECS”) and Technical Support Services (“TSS”) segments during fiscal 2013. The aggregate fair value of the purchase prices for fiscal 2013 acquisitions was $248.9 million.  Of this amount, $171.6 million was paid to the sellers, $2.0 million was recorded as liabilities in accordance with the purchase agreements, and $75.3 million was the estimated fair value of contingent earn-out obligations as of the respective acquisition dates, with an aggregate maximum of $86.7 million upon the achievement of specified financial objectives.  In the first quarter of fiscal 2014, we acquired a company that enhanced our service offerings in our ECS segment.
	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 2013 acquisitions primarily represent the value of workforces with distinct expertise in the solid and hazardous waste, and oil and gas 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.  The purchase price allocations related to acquisitions completed during the second half of fiscal 2013 and the first quarter of fiscal 2014 are preliminary, and subject to adjustment, based on the valuation and final determination of net assets acquired.  We do not believe that any such adjustment will have a material effect on our consolidated results of operations.  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 condensed 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 29, 2013).  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 condensed 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 initial estimates.  Changes in the estimated fair value of our contingent earn-out liabilities related to the time component of the present value calculation are reported in interest expense.  Adjustments to the estimated fair value related to changes in all other unobservable inputs are reported in operating income.  During the three and six months ended March 30, 2014, we recorded net decreases in our contingent earn-out liabilities and reported related net gains in operating income of $21.3 million and $26.0 million, respectively, compared to approximately $1.0 million for both the three and six months ended March 31, 2013.  The fiscal 2014 gains primarily resulted from updated valuations of the contingent consideration liability for Parkland.  We recognized a net unfavorable operating income adjustment for Parkland during the second quarter of fiscal 2014.  As a result, we lowered our income projections over the remaining earn-out period and recorded a corresponding reduction of the earn-out liability.  We also determined that this charge, which related to a single project, would not negatively impact Parkland’s longer-term performance or result in goodwill impairment.  However, if our income projections for Parkland were to decline further, this could result in the impairment of a portion of the related goodwill balance of $96.4 million.  In this event, we would also likely have gains in our operating income up to a maximum of the remaining Parkland contingent consideration liability. Conversely, if Parkland's performance increases beyond our projections, we could incur future losses in operating income if the resulting contingent consideration earned exceeds the current recorded liability.
	At March 30, 2014, there was a total maximum of $78.8 million of outstanding contingent consideration related to completed acquisitions.  Of this amount, $49.1 million was estimated as the fair value and accrued on our condensed consolidated balance sheets.  For the six months ended March 30, 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.  For the six months ended March 31, 2013, we made $24.4 million of earn-out payments to former owners.  Of this amount, we reported $24.0 million as cash used in financing activities and $0.4 million as cash used in operating activities.

Goodwill_and_Intangible_Assets

Goodwill and Intangible Assets	6 Months Ended
	Mar. 30, 2014
Goodwill and Intangible Assets	'
Goodwill and Intangible Assets	'
	4.                                      Goodwill and Intangible Assets
	The following table summarizes the changes in the carrying value of goodwill:
		ECS			TSS			RCM			Total
		(in thousands)
	Balance at September 29, 2013	$	353,608		$	177,579		$	191,605		$	722,792
	Goodwill additions	11,472			–			–			11,472
	Foreign exchange impact	-18,167			-17			-7,053			-25,237
	Goodwill adjustments	–			161			314			475
	Balance at March 30, 2014	$	346,913		$	177,723		$	184,866		$	709,502
	Goodwill additions are attributable to an acquisition completed in the first quarter of fiscal 2014.  Substantially all of the goodwill additions are not deductible for income tax purposes.  The foreign exchange impact relates to our foreign subsidiaries with functional currencies that are different than our reporting currency.  The gross amounts of goodwill for ECS were $404.4 million and $411.1 million at March 30, 2014 and September 29, 2013, respectively, excluding $57.5 million of accumulated impairment.
	We test our goodwill for impairment on an annual basis, and more frequently when an event occurs or circumstances indicate that the carrying value of the asset may not be recoverable.  We perform our annual goodwill impairment review at the beginning of our fiscal fourth quarter.  Our last annual review at July 1, 2013, 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.  During this review we identified three operating units (with goodwill totaling $208.3 million as of March 30, 2014) in the ECS segment and two recently acquired reporting units (with goodwill totaling $135.1 million as of March 30, 2014) in the RCM segment with fair values in excess of their carrying values of less than 20%.  The goodwill related to the three reporting units in the ECS segment was adjusted to fair value in the third quarter of fiscal 2013, and a $56.6 million impairment charge was recorded.  The two reporting units in the RCM segment were acquired at fair value in the second quarter of fiscal 2013.  In addition, we regularly evaluate whether events and circumstances have occurred that may indicate a potential change in recoverability of goodwill.  Based on these assessments as of March 30, 2014, we also determined that all of our reporting units had estimated fair values that were in excess of their carrying values, including goodwill as of March 30, 2014 with the same five reporting units having fair value in excess of carrying value of less than 20%. Although we believe that our estimates of fair value for these reporting units are reasonable, if the financial performance for these reporting units falls significantly below our expectations or market prices for similar businesses decline, the goodwill for these reporting units could become impaired.
	The gross amount and accumulated amortization of our acquired identifiable intangible assets with finite useful lives included in “Intangible assets - net” on the condensed consolidated balance sheets, were as follows:
		March 30, 2014								September 29, 2013
		Weighted-		Gross			Accumulated			Gross			Accumulated
		Average		Amount			Amortization			Amount			Amortization
		Remaining Life
		(in Years)
		($ in thousands)
	Non-compete agreements	2.5		$	2,123		$	-1,345		$	6,160		$	-5,247
	Client relations	4.1		119,364			-51,780			128,839			-49,189
	Backlog	0.5		11,137			-10,159			68,968			-64,675
	Technology and trade names	2.5		3,285			-1,642			4,204			-2,131
	Total			$	135,909		$	-64,926		$	208,171		$	-121,242
	The gross amount and accumulated amortization for acquired identifiable intangible assets decreased due to a write-off of fully amortized assets in the first quarter of fiscal 2014. The recent acquisition added $2.2 million of identifiable intangible assets, partially offset by $2.8 million of foreign currency translation adjustments. Amortization expense for the identifiable intangible assets for the three and six months ended March 30, 2014 was $6.7 million and $15.3 million, respectively, compared to $9.1 million and $14.7 million for the prior-year periods. Estimated amortization expense for the remainder of fiscal 2014 and succeeding years is as follows:
		Amount
		(in thousands)
	2014	$	11,869
	2015	19,267
	2016	15,444
	2017	13,170
	2018	6,283
	Beyond	4,950
	Total	$	70,983

Property_and_Equipment

Property and Equipment	6 Months Ended
	Mar. 30, 2014
Property and Equipment	'
Property and Equipment	'
	5.                                      Property and Equipment
	Property and equipment consisted of the following:
		March 30,		September 29,
		2014		2013
		(in thousands)
	Land and buildings	$	5,372	$	5,565
	Equipment, furniture and fixtures	207,728		210,172
	Leasehold improvements	25,088		26,429
	Total property and equipment	238,188		242,166
	Accumulated depreciation	-157,836		-154,140
	Property and equipment, net	$	80,352	$	88,026
	The depreciation expense related to property and equipment, including assets under capital leases, was $6.6 million and $13.7 million for the three and six months ended March 30, 2014, respectively, compared to $7.5 million and $14.3 million for the prior-year periods.

Stock_Repurchase_and_Dividends

Stock Repurchase and Dividends	6 Months Ended
	Mar. 30, 2014
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 (the “Stock Repurchase Program”) under which we may currently repurchase up to $100 million of our common stock.  In February 2014, our Board of Directors amended the Stock Repurchase Program to authorize the repurchase of up to $30 million of the $100 million Stock Repurchase Program in open market purchases through September 2014, revise the pricing parameters and extend the program through fiscal 2014.  Stock repurchases may be made on the open market or in privately negotiated transactions with third parties.  Because the repurchases under the Stock Repurchase Program are subject to certain pricing parameters, there is no guarantee as to the exact number of shares that will be repurchased under the program.  From the inception of the Stock Repurchase Program through March 30, 2014, we repurchased through open market purchases a total of 1.1 million shares at an average price of $24.61 per share, for a total cost of $26.6 million.
	Subsequent Event.  On April 28, 2014, the Board of Directors declared a quarterly cash dividend of $0.07 per share payable on June 4, 2014 to stockholders of record as of the close of business on May 16, 2014.

Stockholders_Equity_and_Stock_

Stockholders' Equity and Stock Compensation Plans	6 Months Ended
	Mar. 30, 2014
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 30, 2014 was $3.2 million and $5.5 million, respectively, compared to $2.3 million and $4.8 million for the same periods last year.  The majority of these amounts was included in “Selling, general and administrative (“SG&A”) expenses” in our condensed consolidated statements of income.  In the three months ended March 30, 2014, no stock options were granted and we awarded 125 restricted stock units (“RSUs”) to an employee at the fair value of $28.72 per share on the award date.  For the six months ended March 30, 2014, we granted 354,238 stock options with exercise prices of $28.58 - $28.68 per share and an estimated weighted-average fair value of $9.36 per share.  In addition, we awarded 117,067 shares of restricted stock to our non-employee directors and executive officers at the fair value of $28.58 per share on the award date.  All of these shares are performance-based and vest, if at all, over a three-year period.  The number of shares that ultimately vest is based on the growth in our diluted earnings per share. Additionally, we awarded 224,743 RSUs to our non-employee directors, executive officers and employees at the weighted-average fair value of $28.58 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. 30, 2014
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 30,		March 31,		March 30,		March 31,
		2014		2013		2014		2013
		(in thousands, except per share data)
	Net income attributable to Tetra Tech	$	31,709	$	24,820	$	59,023	$	51,043
	Weighted-average common shares outstanding – basic	64,835		64,551		64,670		64,376
	Effect of dilutive stock options and unvested restricted stock	875		921		847		832
	Weighted-average common stock outstanding – diluted	65,710		65,472		65,517		65,208
	Earnings per share attributable to Tetra Tech:
	Basic	$	0.49	$	0.38	$	0.91	$	0.79
	Diluted	$	0.48	$	0.38	$	0.9	$	0.78
	For the three and six months ended March 30, 2014, 0.3 million and no options were excluded from the calculation of dilutive potential common shares, respectively, compared to 0.4 million and 0.6 million 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. 30, 2014
Income Taxes	'
Income Taxes	'
	9.             Income Taxes
	The effective tax rates for the first half of fiscal 2014 and 2013 were 30.3% and 32.7%, respectively.  At March 30, 2014, undistributed earnings of our foreign subsidiaries, primarily in Canada, in the amount of approximately $31.8 million, are expected to be permanently reinvested.  Accordingly, no provision for U.S. income taxes or foreign withholding taxes has been made.  Upon distribution of those earnings, we would be subject to U.S. income taxes and foreign withholding taxes.  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 30, 2014, we performed our assessment of net deferred tax assets.  Significant management judgment is required to determine 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 ended September 28, 2014, 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.  Although we project earnings in the related business beyond 2014, we did not rely on these projections when assessing the realizability of our deferred tax assets.  Based on our assessment, we 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 $7.6 million had been provided in previous years.
	During the second quarter of fiscal 2013, the American Taxpayer Relief Act of 2012 was signed into law.  This law retroactively extended the federal research and experimentation credits (“R&E credits”) for amounts incurred from January 1, 2012 through December 31, 2013.  Our effective tax rate for the first quarter of fiscal 2014 includes a tax benefit from R&E credits attributable to the first three months of fiscal 2014.  Should the R&E credits provision be retroactively extended during fiscal 2014, additional benefits will be reflected in our effective tax rate during the quarter reporting period of enactment.

Reportable_Segments

Reportable Segments	6 Months Ended
	Mar. 30, 2014
Reportable Segments	'
Reportable Segments	'
	10.          Reportable Segments
	Our reportable segments are as follows:
	ECS:  provides front-end science, consulting engineering and project management services in the areas of surface water management, water infrastructure, solid waste management, mining, geotechnical sciences, arctic engineering, industrial processes and oil sands, transportation and information technology.
	TSS:  provides management consulting and engineering services and strategic direction in the areas of environmental assessments/hazardous waste management, climate change, international development, international reconstruction and stabilization, energy, oil and gas, technical government consulting, and building and facilities.
	RCM:  provides full-service support, including construction and construction management, to all of our client sectors, including the U.S. federal government in the United States and internationally, and commercial clients worldwide, in the areas of environmental remediation, infrastructure development, solid waste management, energy, and oil and gas.
	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 30,		March 31,		March 30,		March 31,
		2014		2013		2014		2013
		(in thousands)
	Revenue
	ECS	$	226,088	$	259,194	$	460,975	$	537,361
	TSS	217,295		222,108		437,986		466,032
	RCM	164,225		178,499		378,431		336,930
	Elimination of inter-segment revenue	-21,323		-17,802		-45,259		-39,779
	Total revenue	$	586,285	$	641,999	$	1,232,133	$	1,300,544
	Operating Income (loss)
	ECS	$	11,966	$	11,203	$	31,972	$	30,493
	TSS	23,284		22,262		46,104		44,605
	RCM	-5,497		14,094		3,030		21,176
	Corporate (1)	16,433		-9,892		8,798		-16,798
	Total operating income	$	46,186	$	37,667	$	89,904	$	79,476
	Depreciation
	ECS	$	2,037	$	2,587	$	4,213	$	5,213
	TSS	585		693		1,169		1,475
	RCM	3,219		3,433		6,834		6,035
	Corporate	737		809		1,491		1,607
	Total depreciation	$	6,578	$	7,522	$	13,707	$	14,330
	(1)                Includes amortization of intangibles, other costs and other income not allocable to segments.
		March 30,		September 29,
		2014		2013
		(in thousands)
	Total Assets
	ECS	$	883,135	$	912,996
	TSS	707,808		673,864
	RCM	430,562		435,053
	Corporate (1)	-244,473		-222,821
	Total assets	$	1,777,032	$	1,799,092
	(1)                Corporate assets consist of intercompany eliminations and assets not allocated to 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 30,		March 31,		March 30,		March 31,
		2014		2013		2014		2013
		(in thousands)
	Client Sector
	International (1)	$	181,570	$	196,840	$	345,504	$	364,342
	U.S. commercial	147,854		148,296		334,150		321,442
	U.S. federal government (2)	178,341		206,297		373,525		433,694
	U.S. state and local government	78,520		90,566		178,954		181,066
	Total	$	586,285	$	641,999	$	1,232,133	$	1,300,544
	(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. 30, 2014
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 29, 2013).  The carrying value of our long-term debt approximated fair value at March 30, 2014 and September 29, 2013.  As of March 30, 2014, we had borrowings of $205.0 million under our amended credit agreement to fund our business acquisitions, working capital needs and contingent earn-outs.

Joint_Ventures

Joint Ventures	6 Months Ended
	Mar. 30, 2014
Joint Ventures	'
Joint Ventures	'
	12.          Joint Ventures
	Consolidated Joint Ventures
	The aggregate revenue of our consolidated joint ventures for the three and six months ended March 30, 2014 was $3.5 million and $6.2 million, respectively, compared to $3.0 million and $7.0 million for the same periods last year.  The assets and liabilities of these consolidated joint ventures were immaterial at March 30, 2014 and September 29, 2013.  These assets are restricted for use only by those joint ventures and are not available for our general operations.  For both March 30, 2014 and September 29, 2013, cash and cash equivalents maintained by the consolidated joint ventures were $1.2 million.
	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 30, 2014, we reported $0.8 million and $1.5 million of equity in earnings of unconsolidated joint ventures, respectively, compared to $1.3 million and $1.9 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 aggregate, immaterial to our consolidated financial statements.
	The aggregate carrying values of the assets and liabilities of the unconsolidated joint ventures were $21.3 million and $18.8 million, respectively, at March 30, 2014, and $24.0 million and $21.8 million, respectively, at September 29, 2013.

Derivative_Financial_Instrumen

Derivative Financial Instruments	6 Months Ended
	Mar. 30, 2014
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 have also entered 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.  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.
	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 additional interest rate swap agreements that we designated as cash flow hedges to fix the variable interest rates on the balance of the term loan facility.  At March 30, 2014, the effective portion of our interest rate swap agreements designated as cash flow hedges before tax effect was immaterial, all of which we expect to reclassify from accumulated other comprehensive income to interest expense within the next 12 months.
	As of March 30, 2014, the notional principal, fixed rates and related expiration dates of our outstanding interest rate swap agreements are as follows:
	Notional Amount			Fixed		Expiration
	(in thousands)			Rate		Date
	$	51,250		1.36%		May 2018
	51,250			1.34%		May 2018
	51,250			1.35%		May 2018
	25,625			1.23%		May 2018
	25,625			1.24%		May 2018
	The fair values of our outstanding derivatives designated as hedging instruments are as follows:
			Balance Sheet Location		March 30,		September 29,
					2014		2013
					(in thousands)
	Interest rate swap agreements		Other current liabilities		$	257	$	987
	The impact of the effective portions of derivative instruments in cash flow hedging relationships on income and other comprehensive income from our interest rate swap agreements was immaterial for the first six months of fiscal 2014 and the fiscal year ended September 29, 2013. Additionally, there were no ineffective portions of derivative instruments.  Accordingly, no amounts were excluded from effectiveness testing for our interest rate swap agreements.  We had no derivative instruments that were not designated as hedging instruments for fiscal 2013 and the first half of fiscal 2014.

Reclassifications_Out_of_Accum

Reclassifications Out of Accumulated Other Comprehensive Income (Loss)	6 Months Ended
	Mar. 30, 2014
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 30, 2014 and September 29, 2013 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 30, 2012	$	25,511	$	28	$	25,539
	Other comprehensive (loss) income before reclassifications	-12,134		166		-11,968
	Amounts reclassified from accumulated other comprehensive income
	Foreign exchange contracts, net of tax (1)	—		-194		-194
	Net current-period other comprehensive loss	-12,134		-28		-12,162
	Balances at March 31, 2013	$	13,377	$	—	$	13,377
	Balances at December 29, 2013	$	-19,756	$	343	$	-19,413
	Other comprehensive (loss) income before reclassifications	-15,650		262		-15,388
	Amounts reclassified from accumulated other comprehensive income
	Interest rate contacts, net of tax (2)	—		-648		-648
	Net current-period other comprehensive loss	-15,650		-386		-16,036
	Balances at March 30, 2014	$	-35,406	$	-43	$	-35,449
	(1)                          This accumulated other comprehensive component is reclassified in “Interest expense” and foreign exchange expense in “Selling, general and administrative expenses” in our condensed consolidated statements of income.  See Note 13, “Derivative Financial Instruments”, for more information.
	(2)                          This accumulated other comprehensive component is reclassified in “Interest expense” in our condensed consolidated statements of income.  See Note 13, “Derivative Financial Instruments”, for more information.
		Six Months Ended
		Foreign		Loss on		Accumulated
		Currency		Derivative		Other
		Translation		Instruments		Comprehensive
		Adjustments				Income (Loss)
		(in thousands)
	Balances at September 30, 2012	$	31,110	$	-93	$	31,017
	Other comprehensive (loss) income before reclassifications	-17,733		257		-17,476
	Amounts reclassified from accumulated other comprehensive income
	Foreign exchange contracts, net of tax (1)	—		-164		-164
	Net current-period other comprehensive loss	-17,733		93		-17,640
	Balances at March 31, 2013	$	13,377	$	—	$	13,377
	Balances at September 29, 2013	$	2,340	$	-482	$	1,858
	Other comprehensive (loss) income before reclassifications	-37,746		1,570		-36,176
	Amounts reclassified from accumulated other comprehensive income
	Interest rate contracts, net of tax (2)	—		-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
	(1)                          This accumulated other comprehensive component is reclassified in “Interest expense” and foreign exchange expense in “Selling, general and administrative expenses” in our condensed consolidated statements of income.  See Note 13, “Derivative Financial Instruments”, for more information.
	(2)                          This accumulated other comprehensive component is reclassified in “Interest expense” in our condensed consolidated statements of income.  See Note 13, “Derivative Financial Instruments”, for more information.

Commitments_and_Contingencies

Commitments and Contingencies	6 Months Ended
	Mar. 30, 2014
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 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 through September 2014.  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.
	During late March 2013, the then-president of BPR gave testimony to the Charbonneau Commission, which is investigating possible corruption in the engineering industry in Quebec.  He stated that, during 2007 and 2008, he and other former BPR shareholders paid personal funds to a political party official in exchange for the award of five government contracts.  Further, prior to the testimony, we were not aware of the misconduct.  We have accepted the resignation of BPR’s former president, and are evaluating the impact of these pre-acquisition actions on our business and results of operations.
	During March 2013, following the resignation of BPR’s former president, we learned that criminal charges had been filed against BPR and its former president in France.  The charges relate to allegations that, in 2009, a BPR subsidiary had hired an employee of another firm to be CEO of that BPR subsidiary as a part of a corrupt scheme that allegedly damaged, among others, the employee’s former employer.  A trial in this matter is scheduled for May 2014.
	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.
	On June 28, 2013, a purported securities class action lawsuit was filed against Tetra Tech and two of our officers in United States District Court for the Central District of California.  The action was purportedly brought on behalf of purchasers of our publicly traded securities between May 3, 2012 and June 18, 2013.  The complaint alleges generally that we and those officers violated Sections 10(b) and 20(a) of the Securities Exchange Act of 1934 and related rules because we allegedly failed to take unspecified, “necessary” charges to our accounts receivables and earnings during the class period.  In addition, the complaint alleges that the financial guidance we offered during the class period was intentionally or recklessly false and misleading.  The complaint alleges unspecified damages based on the decline in the market price of our shares following the issuance of revised guidance on June 18, 2013.  On October 30, 2013, plaintiff filed an amended complaint for the same purported class period making essentially the same allegations.  On November 29, 2013, we filed a motion to dismiss the amended complaint, and on January 17, 2014, the Court granted our motion and dismissed the case without prejudice meaning the plaintiff would be allowed to amend the case and replead. Plaintiff subsequently decided not to amend and on April 24, 2014 the plaintiff voluntarily dismissed the case with prejudice.
	Other than the securities class action (which has been terminated) the financial impact to us of the matters discussed above is unknown at this time.

Recent_Accounting_Pronouncemen

Recent Accounting Pronouncements	6 Months Ended
	Mar. 30, 2014
Recent Accounting Pronouncements	'
Recent Accounting Pronouncements	'
	16.          Recent Accounting Pronouncements
	In December 2011, the Financial Accounting Standards Board (“FASB”) issued new guidance to enhance disclosures about financial instruments and derivative instruments that are either offset on the statement of financial position or subject to an enforceable master netting arrangement or similar agreement, irrespective of whether they are offset on the statement of financial position.  We are required to provide both net and gross information for these assets and liabilities in order to facilitate comparability between financial statements prepared on the basis of U.S. GAAP and financial statements prepared on the basis of International Financial Reporting Standards.  This guidance became effective for us in the first quarter of fiscal 2014 on a retrospective basis.  The adoption of this guidance did not have a material impact on our consolidated financial statements.
	In February 2013, the FASB issued an update to the reporting of reclassifications out of accumulated other comprehensive income.  We are required to disclose additional information about changes in and significant items reclassified out of accumulated other comprehensive income. The guidance became effective for us in the first quarter of fiscal 2014.  The adoption of this guidance did not have an impact on our consolidated financial statements.
	In July 2013, the FASB issued an update on an inclusion of the Fed Funds Effective Swap as a benchmark interest rate (Overnight Interest Swap Rate) for hedge accounting purposes.  This guidance permits the Fed Funds Effective Swap Rate to be used as a U.S. benchmark interest rate for hedge accounting purposes under U.S. GAAP.  This guidance became effective prospectively for qualifying new or redesigned hedging relationships entered into on or after July 17, 2013.  The adoption of this guidance did not have a material impact on our consolidated financial statements.
	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 will be effective for us in the first quarter of fiscal 2015.  We do not expect the adoption of this guidance to have an 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.

Accounts_Receivable_Net_and_Re1

Accounts Receivable - Net and Revenue Recognition (Tables)	6 Months Ended
	Mar. 30, 2014
Accounts Receivable - Net and Revenue Recognition	'
Net accounts receivable and billings in excess of costs on uncompleted contracts	'
		March 30,		September 29,
		2014		2013
		(in thousands)
	Billed	$	338,377	$	375,149
	Unbilled	339,638		306,969
	Contract retentions	23,469		23,353
	Total accounts receivable – gross	701,484		705,471
	Allowance for doubtful accounts	-45,003		-44,624
	Total accounts receivable – net	$	656,481	$	660,847
	Billings in excess of costs on uncompleted contracts	$	85,970	$	79,507

Goodwill_and_Intangible_Assets1

Goodwill and Intangible Assets (Tables)	6 Months Ended
	Mar. 30, 2014
Goodwill and Intangible Assets	'
Summary of changes in the carrying value of goodwill	'
		ECS			TSS			RCM			Total
		(in thousands)
	Balance at September 29, 2013	$	353,608		$	177,579		$	191,605		$	722,792
	Goodwill additions	11,472			–			–			11,472
	Foreign exchange impact	-18,167			-17			-7,053			-25,237
	Goodwill adjustments	–			161			314			475
	Balance at March 30, 2014	$	346,913		$	177,723		$	184,866		$	709,502
Summary of acquired identifiable intangible assets with finite useful lives	'
		March 30, 2014								September 29, 2013
		Weighted-		Gross			Accumulated			Gross			Accumulated
		Average		Amount			Amortization			Amount			Amortization
		Remaining Life
		(in Years)
		($ in thousands)
	Non-compete agreements	2.5		$	2,123		$	-1,345		$	6,160		$	-5,247
	Client relations	4.1		119,364			-51,780			128,839			-49,189
	Backlog	0.5		11,137			-10,159			68,968			-64,675
	Technology and trade names	2.5		3,285			-1,642			4,204			-2,131
	Total			$	135,909		$	-64,926		$	208,171		$	-121,242
Estimated amortization expense for the succeeding five years and beyond	'
		Amount
		(in thousands)
	2014	$	11,869
	2015	19,267
	2016	15,444
	2017	13,170
	2018	6,283
	Beyond	4,950
	Total	$	70,983

Property_and_Equipment_Tables

Property and Equipment (Tables)	6 Months Ended
	Mar. 30, 2014
Property and Equipment	'
Schedule of components of property and equipment	'
		March 30,		September 29,
		2014		2013
		(in thousands)
	Land and buildings	$	5,372	$	5,565
	Equipment, furniture and fixtures	207,728		210,172
	Leasehold improvements	25,088		26,429
	Total property and equipment	238,188		242,166
	Accumulated depreciation	-157,836		-154,140
	Property and equipment, net	$	80,352	$	88,026

Earnings_Per_Share_EPS_Tables

Earnings Per Share (''EPS'') (Tables)	6 Months Ended
	Mar. 30, 2014
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 30,		March 31,		March 30,		March 31,
		2014		2013		2014		2013
		(in thousands, except per share data)
	Net income attributable to Tetra Tech	$	31,709	$	24,820	$	59,023	$	51,043
	Weighted-average common shares outstanding – basic	64,835		64,551		64,670		64,376
	Effect of dilutive stock options and unvested restricted stock	875		921		847		832
	Weighted-average common stock outstanding – diluted	65,710		65,472		65,517		65,208
	Earnings per share attributable to Tetra Tech:
	Basic	$	0.49	$	0.38	$	0.91	$	0.79
	Diluted	$	0.48	$	0.38	$	0.9	$	0.78

Reportable_Segments_Tables

Reportable Segments (Tables)	6 Months Ended
	Mar. 30, 2014
Reportable Segments	'
Summarized financial information of reportable segments	'
	Reportable Segments
		Three Months Ended				Six Months Ended
		March 30,		March 31,		March 30,		March 31,
		2014		2013		2014		2013
		(in thousands)
	Revenue
	ECS	$	226,088	$	259,194	$	460,975	$	537,361
	TSS	217,295		222,108		437,986		466,032
	RCM	164,225		178,499		378,431		336,930
	Elimination of inter-segment revenue	-21,323		-17,802		-45,259		-39,779
	Total revenue	$	586,285	$	641,999	$	1,232,133	$	1,300,544
	Operating Income (loss)
	ECS	$	11,966	$	11,203	$	31,972	$	30,493
	TSS	23,284		22,262		46,104		44,605
	RCM	-5,497		14,094		3,030		21,176
	Corporate (1)	16,433		-9,892		8,798		-16,798
	Total operating income	$	46,186	$	37,667	$	89,904	$	79,476
	Depreciation
	ECS	$	2,037	$	2,587	$	4,213	$	5,213
	TSS	585		693		1,169		1,475
	RCM	3,219		3,433		6,834		6,035
	Corporate	737		809		1,491		1,607
	Total depreciation	$	6,578	$	7,522	$	13,707	$	14,330
	(1)                Includes amortization of intangibles, other costs and other income not allocable to segments.
		March 30,		September 29,
		2014		2013
		(in thousands)
	Total Assets
	ECS	$	883,135	$	912,996
	TSS	707,808		673,864
	RCM	430,562		435,053
	Corporate (1)	-244,473		-222,821
	Total assets	$	1,777,032	$	1,799,092
	(1)                Corporate assets consist of intercompany eliminations and assets not allocated to 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 30,		March 31,		March 30,		March 31,
		2014		2013		2014		2013
		(in thousands)
	Client Sector
	International (1)	$	181,570	$	196,840	$	345,504	$	364,342
	U.S. commercial	147,854		148,296		334,150		321,442
	U.S. federal government (2)	178,341		206,297		373,525		433,694
	U.S. state and local government	78,520		90,566		178,954		181,066
	Total	$	586,285	$	641,999	$	1,232,133	$	1,300,544
	(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. 30, 2014
Derivative Financial Instruments	'
Schedule of notional principal, fixed rates and related expiration dates of outstanding interest rate swap agreements	'
	Notional Amount			Fixed		Expiration
	(in thousands)			Rate		Date
	$	51,250		1.36%		May 2018
	51,250			1.34%		May 2018
	51,250			1.35%		May 2018
	25,625			1.23%		May 2018
	25,625			1.24%		May 2018
Schedule of fair values of the entity's outstanding derivatives designated as hedging instruments	'
			Balance Sheet Location		March 30,		September 29,
					2014		2013
					(in thousands)
	Interest rate swap agreements		Other current liabilities		$	257	$	987

Reclassifications_Out_of_Accum1

Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Mar. 30, 2014
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 30, 2012	$	25,511	$	28	$	25,539
	Other comprehensive (loss) income before reclassifications	-12,134		166		-11,968
	Amounts reclassified from accumulated other comprehensive income
	Foreign exchange contracts, net of tax (1)	—		-194		-194
	Net current-period other comprehensive loss	-12,134		-28		-12,162
	Balances at March 31, 2013	$	13,377	$	—	$	13,377
	Balances at December 29, 2013	$	-19,756	$	343	$	-19,413
	Other comprehensive (loss) income before reclassifications	-15,650		262		-15,388
	Amounts reclassified from accumulated other comprehensive income
	Interest rate contacts, net of tax (2)	—		-648		-648
	Net current-period other comprehensive loss	-15,650		-386		-16,036
	Balances at March 30, 2014	$	-35,406	$	-43	$	-35,449
	(1)                          This accumulated other comprehensive component is reclassified in “Interest expense” and foreign exchange expense in “Selling, general and administrative expenses” in our condensed consolidated statements of income.  See Note 13, “Derivative Financial Instruments”, for more information.
	(2)                          This accumulated other comprehensive component is reclassified in “Interest expense” in our condensed consolidated statements of income.  See Note 13, “Derivative Financial Instruments”, for more information.
		Six Months Ended
		Foreign		Loss on		Accumulated
		Currency		Derivative		Other
		Translation		Instruments		Comprehensive
		Adjustments				Income (Loss)
		(in thousands)
	Balances at September 30, 2012	$	31,110	$	-93	$	31,017
	Other comprehensive (loss) income before reclassifications	-17,733		257		-17,476
	Amounts reclassified from accumulated other comprehensive income
	Foreign exchange contracts, net of tax (1)	—		-164		-164
	Net current-period other comprehensive loss	-17,733		93		-17,640
	Balances at March 31, 2013	$	13,377	$	—	$	13,377
	Balances at September 29, 2013	$	2,340	$	-482	$	1,858
	Other comprehensive (loss) income before reclassifications	-37,746		1,570		-36,176
	Amounts reclassified from accumulated other comprehensive income
	Interest rate contracts, net of tax (2)	—		-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
	(1)                          This accumulated other comprehensive component is reclassified in “Interest expense” and foreign exchange expense in “Selling, general and administrative expenses” in our condensed consolidated statements of income.  See Note 13, “Derivative Financial Instruments”, for more information.
	(2)                          This accumulated other comprehensive component is reclassified in “Interest expense” in our condensed consolidated statements of income.  See Note 13, “Derivative Financial Instruments”, for more information.

Accounts_Receivable_Net_and_Re2

Accounts Receivable - Net and Revenue Recognition (Details) (USD $)	3 Months Ended	6 Months Ended		12 Months Ended
	Mar. 30, 2014	Mar. 30, 2014	Mar. 31, 2013	Sep. 29, 2013
Accounts Receivable - Net and Revenue Recognition	'	'	'	'
Billed	$338,377,000	$338,377,000	'	$375,149,000
Unbilled	339,638,000	339,638,000	'	306,969,000
Contract retentions	23,469,000	23,469,000	'	23,353,000
Total accounts receivable - gross	701,484,000	701,484,000	'	705,471,000
Allowance for doubtful accounts	-45,003,000	-45,003,000	'	-44,624,000
Total accounts receivable - net	656,481,000	656,481,000	'	660,847,000
Billings in excess of costs on uncompleted contracts	85,970,000	85,970,000	'	79,507,000
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	61,000,000	61,000,000	'	41,000,000
Charges recorded to reverse profit recognized in prior periods	5,300,000	'	'	'
Percentage of project completed	90.00%	90.00%	'	'
Remaining estimated cost to complete the related contracts	13,000,000	13,000,000	'	'
Additional accounts receivable recorded for project based upon the portion of change orders that the entity believes to have a technical and legal basis for recovery and are probable of collection	10,000,000	10,000,000	'	'
Additional revenue recorded for project based upon the portion of change orders that the entity believes to have a technical and legal basis for recovery and are probable of collection	10,000,000	'	'	'
Revenue recognized related to the evaluation of claim amounts	'	3,400,000	1,100,000	'
Increase in operating income related to the evaluation of claim amounts	'	3,400,000	1,100,000	'
Billed accounts receivable related to U.S. federal government contracts	68,900,000	68,900,000	'	50,500,000
U.S. federal government unbilled receivables, net of progress payments	69,900,000	69,900,000	'	79,300,000
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	5,300,000	5,300,000	'	'
Liability for anticipated losses	9,200,000	9,200,000	'	13,300,000
Estimated cost to complete the related contracts	$41,100,000	$41,100,000	'	'
Accounts Receivable	'	'	'	'
Account receivable major customer	'	'	'	'
Number of clients exceeding threshold	'	0	'	0

Mergers_and_Acquisitions_Detai

Mergers and Acquisitions (Details) (USD $)	3 Months Ended		6 Months Ended				12 Months Ended	6 Months Ended
In Millions, unless otherwise specified	Mar. 30, 2014	Mar. 31, 2013	Mar. 30, 2014	Mar. 31, 2013	Mar. 30, 2014	Mar. 30, 2014	Sep. 29, 2013	Mar. 30, 2014
					Maximum	Minimum	AEG, Parkland and other 2013 acquisitions	Parkland
Business acquisition	'	'	'	'	'	'	'	'
Aggregate fair value of purchase prices	'	'	'	'	'	'	$248.90	'
Cash paid to the sellers	'	'	'	'	'	'	171.6	'
Amount recorded as liabilities in accordance with the purchase agreements	'	'	'	'	'	'	2	'
Estimated fair value of contingent earn-out obligations	49.1	'	49.1	'	'	'	75.3	'
Aggregate maximum of contingent consideration	78.8	'	78.8	'	'	'	86.7	'
Earn out period for operating income projection	'	'	'	'	'3 years	'2 years	'	'
Net decreases in our contingent earn-out liabilities	21.3	1	26	1	'	'	'	'
Net gains on fair value adjustment in operating income	21.3	1	26	1	'	'	'	'
Goodwill balance	'	'	'	'	'	'	'	96.4
Earn-outs paid to former owners	'	'	10.6	24.4	'	'	'	'
Reported as cash used in financing activities	'	'	9.3	24	'	'	'	'
Reported as cash used in operating activities	'	'	$1.30	$0.40	'	'	'	'

Goodwill_and_Intangible_Assets2

Goodwill and Intangible Assets (Details) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Mar. 30, 2014	Sep. 29, 2013
		item
Goodwill	'	'	'
Balance at beginning of the period	'	$722,792,000	'
Goodwill additions	'	11,472,000	'
Foreign exchange impact	'	-25,237,000	'
Goodwill adjustments	'	475,000	'
Balance at end of the period	'	709,502,000	'
Number of reporting units having fair value in excess of carrying value of less than 20%.	'	5	'
Goodwill	'	709,502,000	'
Maximum	'	'	'
Goodwill	'	'	'
Percentage of excess of fair value over carrying value	'	20.00%	'
ECS	'	'	'
Goodwill	'	'	'
Balance at beginning of the period	'	353,608,000	'
Goodwill additions	'	11,472,000	'
Foreign exchange impact	'	-18,167,000	'
Balance at end of the period	'	346,913,000	'
Gross amounts of goodwill	'	404,400,000	411,100,000
Accumulated impairment	'	57,500,000	57,500,000
Impairment of goodwill	56,600,000	'	'
Number of reporting units having fair value in excess of carrying value of less than 20%.	'	3	'
Goodwill	'	346,913,000	'
Represents the goodwill determined to have fair value in excess of carrying value of less than 20%	'	208,300,000	'
ECS | Maximum	'	'	'
Goodwill	'	'	'
Percentage of excess of fair value over carrying value	'	20.00%	'
TSS	'	'	'
Goodwill	'	'	'
Balance at beginning of the period	'	177,579,000	'
Foreign exchange impact	'	-17,000	'
Goodwill adjustments	'	161,000	'
Balance at end of the period	'	177,723,000	'
Goodwill	'	177,723,000	'
RCM	'	'	'
Goodwill	'	'	'
Balance at beginning of the period	'	191,605,000	'
Foreign exchange impact	'	-7,053,000	'
Goodwill adjustments	'	314,000	'
Balance at end of the period	'	184,866,000	'
Number of reporting units having fair value in excess of carrying value of less than 20%.	'	2	'
Goodwill	'	184,866,000	'
Represents the goodwill determined to have fair value in excess of carrying value of less than 20%	'	$135,100,000	'
Number of reporting units recently acquired	'	2	'
RCM | Maximum	'	'	'
Goodwill	'	'	'
Percentage of excess of fair value over carrying value	'	20.00%	'

Goodwill_and_Intangible_Assets3

Goodwill and Intangible Assets (Details 2) (USD $)	3 Months Ended		6 Months Ended
	Mar. 30, 2014	Mar. 31, 2013	Mar. 30, 2014	Mar. 31, 2013	Sep. 29, 2013
Finite-lived intangible assets	'	'	'	'	'
Gross Amount	$135,909,000	'	$135,909,000	'	$208,171,000
Accumulated Amortization	-64,926,000	'	-64,926,000	'	-121,242,000
Identifiable intangible assets added on acquisition	'	'	2,200,000	'	'
Foreign currency translation adjustments	'	'	2,800,000	'	'
Amortization expense for identifiable intangible assets	6,700,000	9,100,000	15,300,000	14,700,000	'
Estimated amortization expense	'	'	'	'	'
2014	11,869,000	'	11,869,000	'	'
2015	19,267,000	'	19,267,000	'	'
2016	15,444,000	'	15,444,000	'	'
2017	13,170,000	'	13,170,000	'	'
2018	6,283,000	'	6,283,000	'	'
Beyond	4,950,000	'	4,950,000	'	'
Total	70,983,000	'	70,983,000	'	'
Non-compete agreements	'	'	'	'	'
Finite-lived intangible assets	'	'	'	'	'
Weighted-Average Remaining Life	'	'	'2 years 6 months	'	'
Gross Amount	2,123,000	'	2,123,000	'	6,160,000
Accumulated Amortization	-1,345,000	'	-1,345,000	'	-5,247,000
Client relations	'	'	'	'	'
Finite-lived intangible assets	'	'	'	'	'
Weighted-Average Remaining Life	'	'	'4 years 1 month 6 days	'	'
Gross Amount	119,364,000	'	119,364,000	'	128,839,000
Accumulated Amortization	-51,780,000	'	-51,780,000	'	-49,189,000
Backlog	'	'	'	'	'
Finite-lived intangible assets	'	'	'	'	'
Weighted-Average Remaining Life	'	'	'6 months	'	'
Gross Amount	11,137,000	'	11,137,000	'	68,968,000
Accumulated Amortization	-10,159,000	'	-10,159,000	'	-64,675,000
Technology and trade names	'	'	'	'	'
Finite-lived intangible assets	'	'	'	'	'
Weighted-Average Remaining Life	'	'	'2 years 6 months	'	'
Gross Amount	3,285,000	'	3,285,000	'	4,204,000
Accumulated Amortization	($1,642,000)	'	($1,642,000)	'	($2,131,000)

Property_and_Equipment_Details

Property and Equipment (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 30, 2014	Mar. 31, 2013	Mar. 30, 2014	Mar. 31, 2013	Sep. 29, 2013
Property and Equipment	'	'	'	'	'
Property and equipment at cost, gross	$238,188	'	$238,188	'	$242,166
Accumulated depreciation	-157,836	'	-157,836	'	-154,140
Property and equipment, net	80,352	'	80,352	'	88,026
Depreciation expense related to property and equipment, including assets under capital leases	6,578	7,522	13,707	14,330	'
Land and buildings	'	'	'	'	'
Property and Equipment	'	'	'	'	'
Property and equipment at cost, gross	5,372	'	5,372	'	5,565
Equipment, furniture and fixtures	'	'	'	'	'
Property and Equipment	'	'	'	'	'
Property and equipment at cost, gross	207,728	'	207,728	'	210,172
Leasehold improvements	'	'	'	'	'
Property and Equipment	'	'	'	'	'
Property and equipment at cost, gross	$25,088	'	$25,088	'	$26,429

Stock_Repurchase_and_Dividends1

Stock Repurchase and Dividends (Details) (USD $)	1 Months Ended		10 Months Ended	0 Months Ended
In Millions, except Per Share data, unless otherwise specified	Feb. 28, 2014	Jun. 30, 2013	Mar. 30, 2014	Apr. 28, 2014
				Subsequent event
Stock Repurchase and Dividends	'	'	'	'
Maximum repurchase amount under stock repurchase program	$30	$100	'	'
Shares repurchased through open market purchases	'	'	1.1	'
Average price of shares repurchased (in dollars per share)	'	'	$24.61	'
Cost of shares repurchased	'	'	$26.60	'
Subsequent Event	'	'	'	'
Quarterly cash dividend declared (in dollars per share)	'	'	'	$0.07

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. 30, 2014	Mar. 31, 2013	Mar. 30, 2014	Mar. 31, 2013
Stockholders' Equity and Stock Compensation Plans	'	'	'	'
Stock-based compensation expense	$3.20	$2.30	$5.50	$4.80
Options granted (in shares)	0	'	354,238	'
Restricted stock award	'	'	'	'
Weighted-average fair value of stock options granted (in dollars per share)	'	'	$9.36	'
Minimum	'	'	'	'
Restricted stock award	'	'	'	'
Exercise price of stock options granted (in dollars per share)	'	'	$28.58	'
Maximum	'	'	'	'
Restricted stock award	'	'	'	'
Exercise price of stock options granted (in dollars per share)	'	'	$28.68	'
Non-employee 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 | Non-employee directors and executive officers	'	'	'	'
Restricted stock award	'	'	'	'
Granted (in shares)	'	'	117,067	'
Granted, fair value (in dollars per share)	'	'	$28.58	'
Vesting period	'	'	'3 years	'
Time-based restricted stock units	'	'	'	'
Restricted stock award	'	'	'	'
Granted (in shares)	125	'	'	'
Granted, fair value (in dollars per share)	$28.72	'	'	'
Time-based restricted stock units | Non-employee directors, executive officers and employees	'	'	'	'
Restricted stock award	'	'	'	'
Granted (in shares)	'	'	224,743	'
Granted, fair value (in dollars per share)	'	'	$28.58	'

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. 30, 2014	Mar. 31, 2013	Mar. 30, 2014	Mar. 31, 2013
Number of weighted-average shares used to compute basic and diluted EPS:	'	'	'	'
Net income attributable to Tetra Tech	$31,709	$24,820	$59,023	$51,043
Weighted-average common shares outstanding - basic	64,835,000	64,551,000	64,670,000	64,376,000
Effect of dilutive stock options and unvested restricted stock	875,000	921,000	847,000	832,000
Weighted-average common stock outstanding - diluted	65,710,000	65,472,000	65,517,000	65,208,000
Earnings per share attributable to Tetra Tech:	'	'	'	'
Basic (in dollars per share)	$0.49	$0.38	$0.91	$0.79
Diluted (in dollars per share)	$0.48	$0.38	$0.90	$0.78
Options	'	'	'	'
Antidilutive securities	'	'	'	'
Securities excluded from the calculation of dilutive potential common shares	300,000	400,000	0	600,000

Income_Taxes_Details

Income Taxes (Details) (USD $)	0 Months Ended	6 Months Ended
In Millions, unless otherwise specified	Sep. 28, 2014	Mar. 30, 2014	Mar. 31, 2013
Income Taxes	'	'	'
Effective tax rate (as a percent)	'	30.30%	32.70%
Undistributed earnings of foreign subsidiaries	'	$31.80	'
Loss carry-forwards in foreign jurisdictions, valuation allowance	'	$7.60	'
Represents the period of projected cumulative pre-tax losses in certain foreign jurisdictions	'36 months	'	'

Reportable_Segments_Details

Reportable Segments (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 30, 2014	Mar. 31, 2013	Mar. 30, 2014	Mar. 31, 2013	Sep. 29, 2013
Financial information concerning reportable segments	'	'	'	'	'
Revenue	$586,285	$641,999	$1,232,133	$1,300,544	'
Operating Income (loss)	46,186	37,667	89,904	79,476	'
Depreciation	6,578	7,522	13,707	14,330	'
Total assets	1,777,032	'	1,777,032	'	1,799,092
Inter-segment elimination	'	'	'	'	'
Financial information concerning reportable segments	'	'	'	'	'
Revenue	-21,323	-17,802	-45,259	-39,779	'
Corporate	'	'	'	'	'
Financial information concerning reportable segments	'	'	'	'	'
Operating Income (loss)	16,433	-9,892	8,798	-16,798	'
Depreciation	737	809	1,491	1,607	'
Corporate	'	'	'	'	'
Financial information concerning reportable segments	'	'	'	'	'
Total assets	-244,473	'	-244,473	'	-222,821
ECS | Operating segment	'	'	'	'	'
Financial information concerning reportable segments	'	'	'	'	'
Revenue	226,088	259,194	460,975	537,361	'
Operating Income (loss)	11,966	11,203	31,972	30,493	'
Depreciation	2,037	2,587	4,213	5,213	'
Total assets	883,135	'	883,135	'	912,996
TSS | Operating segment	'	'	'	'	'
Financial information concerning reportable segments	'	'	'	'	'
Revenue	217,295	222,108	437,986	466,032	'
Operating Income (loss)	23,284	22,262	46,104	44,605	'
Depreciation	585	693	1,169	1,475	'
Total assets	707,808	'	707,808	'	673,864
RCM | Operating segment	'	'	'	'	'
Financial information concerning reportable segments	'	'	'	'	'
Revenue	164,225	178,499	378,431	336,930	'
Operating Income (loss)	-5,497	14,094	3,030	21,176	'
Depreciation	3,219	3,433	6,834	6,035	'
Total assets	$430,562	'	$430,562	'	$435,053

Reportable_Segments_Details_2

Reportable Segments (Details 2) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 30, 2014	Mar. 31, 2013	Mar. 30, 2014	Mar. 31, 2013
Revenue by client sector	'	'	'	'
Threshold percentage for disclosure of revenue from a single client	'	'	10.00%	'
Revenue	$586,285	$641,999	$1,232,133	$1,300,544
Revenue	'	'	'	'
Revenue by client sector	'	'	'	'
Number of clients exceeding threshold	'	'	0	'
International	'	'	'	'
Revenue by client sector	'	'	'	'
Revenue	181,570	196,840	345,504	364,342
U.S. commercial	'	'	'	'
Revenue by client sector	'	'	'	'
Revenue	147,854	148,296	334,150	321,442
U.S. federal government	'	'	'	'
Revenue by client sector	'	'	'	'
Revenue	178,341	206,297	373,525	433,694
U.S. state and local government	'	'	'	'
Revenue by client sector	'	'	'	'
Revenue	$78,520	$90,566	$178,954	$181,066

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Mar. 30, 2014
In Millions, unless otherwise specified
Fair Value Measurements	'
Borrowing under the amended credit agreement	$205

Joint_Ventures_Details

Joint Ventures (Details) (USD $)	3 Months Ended		6 Months Ended
	Mar. 30, 2014	Mar. 31, 2013	Mar. 30, 2014	Mar. 31, 2013	Sep. 29, 2013
Aggregate revenue of consolidated joint ventures	$586,285,000	$641,999,000	$1,232,133,000	$1,300,544,000	'
Unconsolidated Joint Ventures	'	'	'	'	'
Equity in earnings from unconsolidated joint ventures	800,000	1,300,000	1,492,000	1,929,000	'
Carrying value of assets of unconsolidated joint ventures	21,300,000	'	21,300,000	'	24,000,000
Carrying value of liabilities of unconsolidated joint ventures	18,800,000	'	18,800,000	'	21,800,000
Consolidated Joint Ventures	'	'	'	'	'
Aggregate revenue of consolidated joint ventures	3,500,000	3,000,000	6,200,000	7,000,000	'
Restricted cash and cash equivalents of consolidated joint ventures	$1,200,000	'	$1,200,000	'	$1,200,000

Derivative_Financial_Instrumen2

Derivative Financial Instruments (Details) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Dec. 29, 2013	Mar. 30, 2014	Sep. 29, 2013
	item		item
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	'
Interest rate swap agreements | Designated as cash flow hedges | Derivatives designated as hedging instruments	'	'	'
Derivative financial instruments	'	'	'
Number of derivative agreements	2	'	3
Period of reclassification from accumulated other comprehensive income to interest expense	'	'12 months	'
Interest rate swap agreement bearing fixed rate 1.36% | Designated as cash flow hedges | Derivatives designated as hedging instruments	'	'	'
Derivative financial instruments	'	'	'
Notional Amount	'	51,250,000	'
Fixed Rate (as a percent)	'	1.36%	'
Interest rate swap agreement bearing fixed rate 1.34% | Designated as cash flow hedges | Derivatives designated as hedging instruments	'	'	'
Derivative financial instruments	'	'	'
Notional Amount	'	51,250,000	'
Fixed Rate (as a percent)	'	1.34%	'
Interest rate swap agreement bearing fixed rate 1.35% | Designated as cash flow hedges | Derivatives designated as hedging instruments	'	'	'
Derivative financial instruments	'	'	'
Notional Amount	'	51,250,000	'
Fixed Rate (as a percent)	'	1.35%	'
Interest rate swap agreement bearing fixed rate 1.23% | Designated as cash flow hedges | Derivatives designated as hedging instruments	'	'	'
Derivative financial instruments	'	'	'
Notional Amount	'	25,625,000	'
Fixed Rate (as a percent)	'	1.23%	'
Interest rate swap agreement bearing fixed rate 1.24% | Designated as cash flow hedges | Derivatives designated as hedging instruments	'	'	'
Derivative financial instruments	'	'	'
Notional Amount	'	25,625,000	'
Fixed Rate (as a percent)	'	1.24%	'

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. 30, 2014	Sep. 29, 2013
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	$257	$987

Reclassifications_Out_of_Accum2

Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) (USD $)

Mar. 30, 2014

Sep. 29, 2013

Mar. 30, 2014

Mar. 31, 2013

Mar. 30, 2014

Mar. 31, 2013

Mar. 30, 2014

Mar. 31, 2013

Mar. 30, 2014

Mar. 31, 2013

Mar. 31, 2013

Mar. 31, 2013

Mar. 30, 2014

Mar. 30, 2014

Mar. 30, 2014

Mar. 31, 2013

Mar. 30, 2014

Mar. 31, 2013

Mar. 31, 2013

Mar. 31, 2013

Mar. 30, 2014

Mar. 30, 2014

In Thousands, unless otherwise specified

Foreign Currency Translation Adjustments

Foreign Currency Translation Adjustments

Foreign Currency Translation Adjustments

Foreign Currency Translation Adjustments

Loss on Derivative Instruments

Loss on Derivative Instruments

Loss on Derivative Instruments

Loss on Derivative Instruments

Loss on Derivative Instruments

Loss on Derivative Instruments

Loss on Derivative Instruments

Loss on Derivative Instruments

Accumulated Other Comprehensive Income (Loss)

Accumulated Other Comprehensive Income (Loss)

Accumulated Other Comprehensive Income (Loss)

Accumulated Other Comprehensive Income (Loss)

Accumulated Other Comprehensive Income (Loss)

Accumulated Other Comprehensive Income (Loss)

Accumulated Other Comprehensive Income (Loss)

Accumulated Other Comprehensive Income (Loss)

Foreign exchange contracts

Foreign exchange contracts

Interest rate contracts

Interest rate contracts

Foreign exchange contracts

Foreign exchange contracts

Interest rate contracts

Interest rate contracts

Reclassifications out of accumulated other comprehensive income (loss)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Balances at the beginning of the period

($35,449)

$1,858

($19,756)

$25,511

$2,340

$31,110

$343

$28

($482)

($93)

'

'

'

'

($19,413)

$25,539

$1,858

$31,107

'

'

'

'

Other comprehensive (loss) income before reclassifications

'

'

-15,650

-12,134

-37,746

-17,733

262

166

1,570

257

'

'

'

'

-15,388

-11,968

-36,176

-17,476

'

'

'

'

Amounts reclassified from accumulated other comprehensive income

'

'

'

'

'

'

'

'

'

'

-194

-164

-648

-1,131

'

'

'

'

-194

-164

-648

-1,131

Net current-period other comprehensive loss

'

'

-15,650

-12,134

-37,746

-17,733

-386

-28

439

-93

'

'

'

'

-16,036

-12,162

-37,307

-17,640

'

'

'

'

Balances at the end of the period

($35,449)

$1,858

($35,406)

$13,377

($35,406)

$13,377

($43)

'

($43)

'

'

'

'

'

($35,449)

$13,377

($35,449)

$13,377

'

'

'

'

Commitments_and_Contingencies_

Commitments and Contingencies (Details)	Mar. 31, 2013	Apr. 17, 2012	Jun. 28, 2013
	BPR Triax	BPR Triax	Violation of Section 10(b) and 20(a) of the Securities Exchange Act of 1934 and related rules thereof
	item	employee	item
Loss contingencies	'	'	'
Number of employees of BPR Triax charged with allegations of corruption	'	2	'
Number of government contracts cited in testimony	5	'	'
Number of officers against whom complaint was filed	'	'	2