Workers' Compensation Claims - Additional Information (Detail) - USD ($)			6 Months Ended		12 Months Ended	36 Months Ended
	Jul. 01, 2021	Jun. 29, 2020	Jun. 30, 2024	Jun. 30, 2020	Dec. 31, 2023	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Description of renewed agreement						Effective July 1, 2021, the Company entered into a fully insured arrangement for its insured program, whereby third-party insurers assume substantially all risk of loss for claims incurred under the program. This fully insured arrangement has been extended annually and covers claims incurred between July 1, 2021 and June 30, 2025, with an option to renew through June 30, 2026.Each annual fully insured policy allows for BBSI to participate in savings if claims develop favorably up to a maximum per policy year ranging from $20.5 million to $28.5 million, depending on the policy period. For only the policy period from July 1, 2021 to June 30 2022, BBSI can also incur additional premium up to $7.5 million if claims develop adversely. No additional premium can be charged based on claim performance for other policy years.Premiums incurred but not paid are recorded as either current or long-term premium payable on the consolidated balance sheets based on the expected timing of the payments.
Maximum additional premium charged amount for twelve month policy period, if claims develop adversely			$ 0
Balance in Chubb trust accounts			181,300,000		$ 210,900,000	$ 181,300,000
Workers compensation liability			149,630,000		167,763,000	149,630,000	$ 158,054,000	$ 191,822,000	$ 201,641,000	$ 215,987,000
Collateral securities maintain to cover potential workers compensation claims losses			47,000,000		48,100,000	47,000,000
Surety bonds and standby letters of credit			47,000,000			47,000,000
Reserves and IBNR in excess of retention limits incurred but not reported			6,100,000		6,000,000.0
2021-2022 Policy [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum additional premium charged amount for twelve month policy period, if claims develop adversely			7,500,000
2021-2022 Policy [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum savings amount for twelve month policy period, if claims develop favorably			28,500,000
2021-2022 Policy [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum savings amount for twelve month policy period, if claims develop favorably			20,500,000
2022-2023 Policy [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum savings amount for twelve month policy period, if claims develop favorably			28,500,000
2022-2023 Policy [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum savings amount for twelve month policy period, if claims develop favorably			20,500,000
2023-2024 Policy [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum savings amount for twelve month policy period, if claims develop favorably			28,500,000
2023-2024 Policy [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum savings amount for twelve month policy period, if claims develop favorably			20,500,000
Other Assets [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Accrual for costs incurred in excess of retention limits offset by a receivable			$ 6,100,000		$ 6,000,000	6,100,000
Self Insured Programs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of worker's compensation exposure covered			15.00%
Worker's compensation risk claim maximum			$ 3,000,000.0	$ 5,000,000.0
Self Insured Programs [Member] | Maryland [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reinsurance coverage			1,000,000.0	1,000,000.0		1,000,000.0
Self Insured Programs [Member] | Colorado [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reinsurance coverage			$ 2,000,000.0	$ 2,000,000.0		$ 2,000,000.0
Insured Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of worker's compensation exposure covered			85.00%
Worker's compensation risk claim maximum	$ 3,000,000
Worker's compensation risk claim maximum		$ 5,000,000