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Workers' Compensation Claims - Summarizes Aggregate Workers' Compensation Reserve Activity (Parenthetical) (Detail) $ in Millions | 6 Months Ended
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Jun. 30, 2021 USD ($)
Third-party Insurance Carrier [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Claim payments related to prior period includes amount payable | $ 47.4

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- Definition Claim payments related to prior period includes amount payable. + References No definition available. + Details
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Namespace Prefix: | bbsi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | bbsi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=bbsi_ThirdPartyInsuranceCarrierMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |