Summary of Significant Accounting Policies - Revenue Recognition and Allowances for Accounts Receivable and Unbilled Services (Details)	12 Months Ended
Dec. 28, 2019
Minimum
Revenue Recognition
Period in which engagements are generally completed	3 months
Maximum
Revenue Recognition
Period in which engagements are generally completed	6 months

Represents the period in which engagements of the entity are completed.

No definition available.

Name:	crai_PeriodInWhichEngagementsAreCompleted
Namespace Prefix:	crai_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration