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Summary of Significant Accounting Policies - Description of Business and Fiscal Year (Details) | 12 Months Ended
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Dec. 29, 2018 segment item | Dec. 30, 2017 item | Dec. 31, 2016 item
Description of Business |  |  |
Number of broad areas of consulting services | 2 |  |
Number of business segment | segment | 1 |  |
Fiscal Year |  |  |
Number of weeks periodically contained in a fiscal year | 53 |  |
Number of weeks in a fiscal year | 52 | 52 | 52

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 Number of broad areas in consulting services offered by the reporting entity. + References No definition available. + Details
Name: | crai_NumberOfBroadAreasOfConsultingServices
Namespace Prefix: | crai_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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

X
- Definition Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues. + References No definition available. + Details
Name: | us-gaap_NumberOfOperatingSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration