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Cover - USD ($)
$ in Billions
 12 Months Ended
Oct. 02, 2022
Nov. 09, 2022
Apr. 03, 2022
Cover [Abstract]      
Document Type 10-K/A    
Amendment Flag false    
Document Annual Report true    
Document Transition Report false    
Document Period End Date Oct. 02, 2022    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2022    
Current Fiscal Year End Date --10-02    
Entity File Number 0-19655    
Entity Registrant Name TETRA TECH, INC.    
Entity Central Index Key 0000831641    
Entity Tax Identification Number 95-4148514    
Entity Incorporation, State or Country Code DE    
Entity Address, Address Line One 3475 East Foothill Boulevard    
Entity Address, City or Town Pasadena    
Entity Address, State or Province CA    
Entity Address, Postal Zip Code 91107    
City Area Code 626    
Local Phone Number 351-4664    
Title of 12(b) Security Common Stock, $0.01 par value    
Trading Symbol TTEK    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 8.9
Entity Common Stock, Shares Outstanding   52,981,143  
Documents Incorporated by Reference [Text Block]

DOCUMENT INCORPORATED BY REFERENCE

 

Portions of registrant’s Proxy Statement for its 2023 Annual Meeting of Stockholders are incorporated by reference in Part III of this report where indicated.

    
ICFR Auditor Attestation Flag true    
Auditor Firm ID 238    
Auditor Name PricewaterhouseCoopers LLP    
Auditor Location Los Angeles, California