Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Jan. 03, 2025	Feb. 21, 2025	Jun. 28, 2024
Cover [Abstract]
Document Type	10-K/A
Amendment Flag	true
Amendment Description	The Registrant is filing this Amendment No. 1 on Form 10-K/A (this “Amendment”) to its Annual Report on Form 10-K for the fiscal year ended January 3, 2025 (the “Original Form 10-K”) to correct the hyperlink for Exhibit 3.2(i). Unless expressly stated, this Amendment does not reflect events occurring after the filing of the Original Form 10-K and does not modify or update in any way the disclosures contained in the Original Form 10-K, which speak as of the date of the Original Form 10-K. Accordingly, this Amendment should be read in conjunction with the Original Form 10-K and the Company’s other filings with the Securities and Exchange Commission subsequent to the filing of the Original Form 10-K. Pursuant to Rule 12b-15 under the Securities Exchange Act of 1934, as amended, this Amendment contains new certifications pursuant to Section 302 of the Sarbanes-Oxley Act of 2002, which are attached hereto.
Document Period End Date	Jan. 03, 2025
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	FY
Entity Registrant Name	EXPONENT, INC.
Entity Central Index Key	0000851520
Current Fiscal Year End Date	--01-03
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 3.7
Trading Symbol	EXPO
Entity Common Stock, Shares Outstanding		50,818,234
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	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 Annual Report	true
Document Transition Report	false
ICFR Auditor Attestation Flag	true
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
Auditor Firm ID	185
Auditor Name	KPMG, LLP
Auditor Location	San Francisco, California
Document Financial Statement Error Correction [Flag]	false
Documents Incorporated by Reference	Portions of the registrant’s Definitive Proxy Statement for the registrant’s 2025 Annual Meeting of Stockholders to be held on June 5, 2025 are incorporated by reference into Part III of this Annual Report on Form 10-K.

EXPONENT INC 10-K/A