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Summary of Significant Accounting Policies - Revenue Recognition (Details)	12 Months Ended
	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

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Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

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Namespace Prefix:	crai_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: