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Summary of Significant Accounting Policies - Revenue Recognition (Details) | 12 Months Ended
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Dec. 29, 2018
Minimum |
Revenue Recognition |
Period in which engagements are generally completed | 3 months
Maximum |
Revenue Recognition |
Period in which engagements are generally completed | 6 months

X
- Definition Represents the period in which engagements of the entity are completed. + References No definition available. + Details
Name: | crai_PeriodInWhichEngagementsAreCompleted
Namespace Prefix: | crai_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | crai_RevenueRecognitionLineItems
Namespace Prefix: | crai_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |