Workers' Compensation Claims - Additional Information (Detail) - USD ($)		6 Months Ended	12 Months Ended
	Jul. 01, 2018	Jun. 30, 2018	Dec. 31, 2017	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Balance in Chubb trust accounts		$ 408,100,000	$ 380,600,000
Specified investment balances or other financial instruments		85,100,000	96,800,000
Surety bonds and standby letters of credit		85,100,000
Estimated future liability for unsettled workers' compensation		390,814,000	363,517,000	$ 378,874,000	$ 330,079,000	$ 326,233,000	$ 312,537,000
Reserves incurred in excess of retention limits		2,900,000	3,000,000
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		2,900,000	$ 3,000,000
California [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Surety bonds and standby letters of credit		70,600,000
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Worker's compensation risk claim maximum	$ 5,000,000
Surety bonds	30,000,000
Subsequent Event [Member] | Wells Fargo Bank, National Association [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Letter of credit	$ 63,700,000
Barrett Business Services Inc [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Worker's compensation risk claim maximum		$ 5,000,000