v3.25.2
Document and Entity Information - shares
6 Months Ended
Jul. 04, 2025
Aug. 01, 2025
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jul. 04, 2025  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q2  
Entity Registrant Name EXPONENT, INC.  
Entity Central Index Key 0000851520  
Current Fiscal Year End Date --01-02  
Entity Current Reporting Status Yes  
Entity Filer Category Large Accelerated Filer  
Trading Symbol EXPO  
Entity Common Stock, Shares Outstanding   50,501,135
Entity Emerging Growth Company false  
Entity Small Business false  
Entity Shell Company false  
Entity File Number 0-18655  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 77-0218904  
Entity Address, Address Line One 149 COMMONWEALTH DRIVE  
Entity Address, City or Town MENLO PARK  
Entity Address, State or Province CA  
Entity Address, Postal Zip Code 94025  
City Area Code 650  
Local Phone Number 326-9400  
Document Quarterly Report true  
Document Transition Report false  
Entity Interactive Data Current Yes  
Title of each class Common Stock, par value $0.001 per share  
Name of each exchange on which registered NASDAQ