XML 79 R57.htm IDEA: XBRL DOCUMENT
v3.25.3

Basis of Presentation - Contingent Consideration, and Concentration of Credit Risk (Details) | 12 Months Ended
--- | ---
Sep. 28, 2025 Institution
Concentration of Credit Risk |
Financial institutions, in any such number of which investment exposure is limited | 1
Accounts receivable due from various agencies of the U.S. federal government (as a percent) | 27.00%
U.S. government |
Concentration of Credit Risk |
Revenue from customers (as a percent) | 32.00%
U.S. state and local government |
Concentration of Credit Risk |
Revenue from customers (as a percent) | 14.00%
U.S. commercial |
Concentration of Credit Risk |
Revenue from customers (as a percent) | 17.00%
International |
Concentration of Credit Risk |
Revenue from customers (as a percent) | 37.00%
Minimum |
Contingent Consideration |
Earn-out period | 3 years
Maximum |
Contingent Consideration |
Earn-out period | 5 years

X
- Definition Business Combination, Contingent Consideration Arrangements, Earn Out Period + References No definition available. + Details
Name: | ttek_BusinessCombinationContingentConsiderationArrangementsEarnOutPeriod
Namespace Prefix: | ttek_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents a number of financial institutions, in any such number of which the entity limits the amount of investment exposure in order to control credit risk. + References No definition available. + Details
Name: | ttek_ConcentrationOfCreditRiskNumberOfFinancialInstitutionsForInvestmentExposure
Namespace Prefix: | ttek_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the percentage of accounts receivable due from various agencies of the U.S. federal government. + References No definition available. + Details
Name: | ttek_PercentageOfAccountReceivablesDueFromAgencies
Namespace Prefix: | ttek_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the percentage of revenue from customers within the risk category. + References No definition available. + Details
Name: | ttek_PercentageOfRevenueEarnedFromAgencies
Namespace Prefix: | ttek_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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

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

X
- Details
Name: | srt_MajorCustomersAxis=ttek_FederalGovernmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_MajorCustomersAxis=ttek_StateAndLocalGovernmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_MajorCustomersAxis=ttek_CommercialMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_MajorCustomersAxis=ttek_InternationalMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |