Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

+ Details

Name:	us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 350
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482665/350-30-50-1

+ Details

Name:	us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of increase in assets, excluding financial assets, lacking physical substance with a definite life, from an acquisition.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482665/350-30-50-1

+ Details

Name:	us-gaap_FinitelivedIntangibleAssetsAcquired1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_OrderOrProductionBacklogMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_TradeNamesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CustomerRelationshipsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ttek_RPSGroupPLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Acquisitions - Schedule of Intangible Assets Assumed (Details) - USD ($) $ in Thousands		3 Months Ended
	Jan. 23, 2023	Dec. 31, 2023
Backlog
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average Amortization Period (in years)		9 months 18 days
Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average Amortization Period (in years)		2 years 1 month 6 days
Client relations
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average Amortization Period (in years)		9 years 2 months 12 days
RPS Group PLC
Acquired Finite-Lived Intangible Assets [Line Items]
Fair Value	$ 174,094
Weighted-average Amortization Period (in years)	8 years 3 months 18 days
RPS Group PLC \| Backlog
Acquired Finite-Lived Intangible Assets [Line Items]
Fair Value	$ 27,880
Weighted-average Amortization Period (in years)	1 year 7 months 6 days
RPS Group PLC \| Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Fair Value	$ 27,260
Weighted-average Amortization Period (in years)	3 years
RPS Group PLC \| Client relations
Acquired Finite-Lived Intangible Assets [Line Items]
Fair Value	$ 118,954
Weighted-average Amortization Period (in years)	11 years 1 month 6 days