Fair Value Measurement - Summary of Investments Measured at Fair Value on Recurring Basis (Parenthetical) (Detail) $ in Millions	Jun. 30, 2018 USD ($)
Fair Value Disclosures [Abstract]
Restricted cash and long term workers' compensation deposits	$ 20.5

Restricted cash and long term workers compensation deposits.

No definition available.

Name:	bbsi_RestrictedCashAndLongTermWorkersCompensationDeposits
Namespace Prefix:	bbsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant