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Summary of Significant Accounting Policies - Description and Fiscal Year (Details) - item | 12 Months Ended
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Dec. 31, 2016 | Jan. 02, 2016 | Jan. 03, 2015
Description of Business |  |  |
Number of broad areas of services | 2 |  |
Fiscal Year |  |  |
Number of weeks periodically contained in a fiscal year | 53 |  |
Number of weeks in a fiscal year | 52 | 52 | 53

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

X
- Definition n/a + References No definition available. + Details
Name: | crai_FiscalYearChangeAbstract
Namespace Prefix: | crai_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the area of services broadly offered by the entity. + References No definition available. + Details
Name: | crai_NumberOfAreasOfServices
Namespace Prefix: | crai_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of weeks in a fiscal year. + References No definition available. + Details
Name: | crai_NumberOfWeeksInFiscalYear
Namespace Prefix: | crai_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of weeks periodically contained in a fiscal year. + References No definition available. + Details
Name: | crai_NumberOfWeeksPeriodicallyContainedInFiscalYear
Namespace Prefix: | crai_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration