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Fair Value Measurement - Summary of Investments Measured at Fair Value on Recurring Basis (Parenthetical) (Detail) $ in Millions | Dec. 31, 2017 USD ($)
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Fair Value Disclosures [Abstract] |
Restricted cash and long term workers' compensation deposits | $ 6.3

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- Definition Restricted cash and long term workers compensation deposits. + References No definition available. + Details
Name: | bbsi_RestrictedCashAndLongTermWorkersCompensationDeposits
Namespace Prefix: | bbsi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_FairValueDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration