Cover - USD ($) $ in Millions	12 Months Ended
	Jan. 01, 2022	Feb. 25, 2022	Jul. 03, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Jan. 01, 2022
Current Fiscal Year End Date	--01-01
Document Transition Report	false
Entity File Number	000-24049
Entity Registrant Name	CRA International, Inc.
Entity Incorporation, State or Country Code	MA
Entity Address, Address Line One	200 Clarendon Street
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Tax Identification Number	04-2372210
Entity Address, Postal Zip Code	02116-5092
City Area Code	617
Local Phone Number	425-3000
Title of 12(b) Security	Common Stock, no par value
Trading Symbol	CRAI
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 601.0
Entity Common Stock, Shares Outstanding		7,400,209
Documents Incorporated by Reference	The information required for Part III of this annual report is incorporated by reference from the registrant's definitive proxy statement for the 2021 annual meeting of its shareholders to be filed with the Securities and Exchange Commission within 120 days after the end of the registrant's fiscal year ended January 1, 2022.
Entity Central Index Key	0001053706
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY