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Basis of Presentation and Preparation - Revenue Recognition and Contract Costs (Details) | 12 Months Ended
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Sep. 30, 2018 Contract
Organization, Consolidation and Presentation of Financial Statements [Abstract] |
Number of types of contracts under which revenue is recognized | 3

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- Definition Represents the number of types of contracts under which revenue is recognized for work performed. + References No definition available. + Details
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Namespace Prefix: | ttek_
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Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract
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