Workers' Compensation Claims - Additional Information (Detail) - USD ($)			3 Months Ended		12 Months Ended
	Jul. 01, 2021	Jun. 29, 2020	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Description of renewed agreement			The Company entered into a new arrangement for its insured program effective July 1, 2021 whereby third-party insurers assume all risk of loss for claims incurred after June 30, 2021. The agreement continues to June 30, 2022 and includes a renewal commitment through June 30, 2023. The arrangement allows for premium adjustments depending on overall portfolio performance. If claims develop favorably, BBSI can participate in the savings up to $20.0 million for a twelve-month policy period. If claims develop adversely, additional premium may be charged up to $7.5 million for a twelve-month policy period.
Maximum savings amount for twelve month policy period, if claims develop favorably			$ 20,000,000.0
Maximum additional premium charged amount for twelve month policy period, if claims develop adversely			7,500,000
Balance in Chubb trust accounts		$ 115,700,000	240,400,000		$ 273,600,000
Workers compensation liability			262,646,000	$ 362,663,000	279,407,000	$ 357,746,000
Workers compensation liability, current			75,893,000		80,028,000
Collateral securities maintain to cover potential workers compensation claims losses			58,400,000		58,400,000
Surety bonds and standby letters of credit			58,400,000
Reserves incurred in excess of retention limits			2,300,000		2,200,000
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			2,300,000		$ 2,200,000
California [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Surety bonds and standby letters of credit			$ 32,600,000
Insured Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of worker's compensation exposure covered			82.00%
Worker's compensation risk claim maximum	$ 3,000,000.0
Worker's compensation risk claim maximum		$ 5,000,000.0
Workers compensation liability			$ 53,100,000
Workers compensation liability, current			$ 5,000,000.0
Self Insured Programs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of worker's compensation exposure covered			18.00%
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
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