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Basis of Presentation and Preparation - Cash and Cash Equivalents and Accounts Receivable (Details) | 12 Months Ended
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Oct. 03, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract] |
Maximum term of original maturity to classify instrument as cash equivalent | 90 days
Period for billing and collecting unbilled receivables | 12 months

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- Definition Represents the maximum original term to maturity of an instrument to classify it as a cash equivalent. + References No definition available. + Details
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Namespace Prefix: | ttek_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Represents the period within which substantially all unbilled receivables are expected to be billed and collected. + References No definition available. + Details
Name: | ttek_UnbilledContractsReceivablePeriodForBillingAndCollection
Namespace Prefix: | ttek_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration