Accounts Receivable - Net (Details) (USD $)	9 Months Ended	12 Months Ended
Jul. 03, 2011	Oct. 03, 2010
Accounts Receivable - Net
Billed	$ 372,771,000	$ 314,905,000
Unbilled	316,367,000	271,643,000
Contract retentions	13,890,000	13,020,000
Total accounts receivable - gross	703,028,000	599,568,000
Allowance for doubtful accounts	(33,897,000)	(32,926,000)
Total accounts receivable - net	669,131,000	566,642,000
Current billings in excess of costs on uncompleted contracts	83,907,000	79,401,000
Non-current billings in excess of costs on uncompleted contracts	6,194,000	5,820,000
Total billings in excess of costs on uncompleted contracts	90,101,000	85,221,000
Period for billing and collecting unbilled receivables (in months)	12
Period for earning majority of billings in excess of costs (in months)	12
Billed accounts receivable related to U.S. federal government contracts	96,000,000	86,300,000
U.S. federal government unbilled receivables, net of progress payments	$ 97,600,000	$ 102,000,000
Threshold percentage for disclosure of accounts receivable from a single client (as a percent)	10.00%	10.00%

Name:	ttek_AccountsReceivableNetDisclosureAbstract
Namespace Prefix:	ttek
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Liability attributable to (i) billings in excess of costs under the percentage of completion contract accounting method representing the difference between contractually invoiced amounts (billings) and revenue recognized based, for example, on costs incurred to estimated total costs at period end or (ii) contractually invoiced amounts (billings) in excess of costs incurred and accumulated under the completed contract accounting method that are expected to be realized within one year or one operating cycle, whichever is longer, from the reporting date.

+ Details

Name:	ttek_BillingsInExcessOfCostCurrent
Namespace Prefix:	ttek
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Liability attributable to (i) billings in excess of costs under the percentage of completion contract accounting method representing the difference between contractually invoiced amounts (billings) and revenue recognized based, for example, on costs incurred to estimated total costs at period end or (ii) contractually invoiced amounts (billings) in excess of costs incurred and accumulated under the completed contract accounting method that are expected to be realized more than one year or one operating cycle, whichever is longer, from the reporting date.

+ Details

Name:	ttek_BillingsInExcessOfCostNoncurrent
Namespace Prefix:	ttek
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the period within which the majority of billings in excess of costs on uncompleted contracts will be earned.

+ Details

Name:	ttek_BillingsInExcessOfCostPeriodForRevenueRecognition
Namespace Prefix:	ttek
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum percentage of accounts receivable from a single client that is used as a threshold for disclosure of a concentration of risk.

+ Details

Name:	ttek_ConcentrationOfRiskAccountsReceivablePercentageMinimum
Namespace Prefix:	ttek
Data Type:	us-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of billed receivables that are derived from government contracts.

+ Details

Name:	ttek_GovernmentContractReceivableBilledAmounts
Namespace Prefix:	ttek
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Unbilled amounts (net of unliquidated progress payments) of government contract receivables.

+ Details

Name:	ttek_GovernmentContractReceivableUnbilledAmounts
Namespace Prefix:	ttek
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the period within which substantially all unbilled receivables are expected to be billed and collected.

+ Details

Name:	ttek_UnbilledContractsReceivablePeriodForBillingAndCollection
Namespace Prefix:	ttek
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 3
-Subparagraph a, b
-Article 5

+ Details

Name:	us-gaap_AccountsReceivableGrossCurrent
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 3
-Subparagraph a(1)
-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 4
-Article 5

+ Details

Name:	us-gaap_AccountsReceivableNetCurrent
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 4
-Article 5

+ Details

Name:	us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amounts due for billed services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the Company and, at a minimum, one other party. An example would be amounts billed to customers under contracts or programs but not paid as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 3
-Article 5

+ Details

Name:	us-gaap_BilledContractReceivables
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Liabilities due to billings on long term contracts that exceed the income recorded under the percentage of completion contract accounting method, or that exceed the accumulated costs under the completed contract accounting method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 45
-Paragraph 5, 12

+ Details

Name:	us-gaap_BillingsInExcessOfCost
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amounts due for services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the Entity and, at a minimum, one other party, which amounts are withheld by the contracting party pending the Entity's compliance or performance in conformity with the terms of the contract. Such billed but unpaid amounts are generally expected to be collected upon complying with certain contractual terms or satisfaction and release by the contracting party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 3
-Subparagraph c(1)
-Article 5

+ Details

Name:	us-gaap_ContractReceivableRetainage
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Unbilled amounts due for services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the entity and, at a minimum, one other party. An example would be amounts associated with contracts or programs where the recognized revenue for performance thereunder exceeds the amounts billed under the terms thereof as of the date of the balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 3
-Subparagraph c(3)
-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 43
-Chapter 11
-Section A
-Paragraph 4, 21

+ Details

Name:	us-gaap_UnbilledContractsReceivable
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant