Workers' Compensation Claims - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016	Mar. 31, 2017	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Balance in Chubb trust account	$ 327,900,000	$ 277,100,000
Specified investment balances or other financial instruments	97,000,000	135,000,000
Surety bonds and standby letters of credit	90,800,000
Estimated future liability for unsettled workers' compensation	330,079,000	312,537,000	$ 326,233,000	$ 277,050,000	$ 265,142,000	$ 255,675,000
Reserves incurred in excess of retention limits	3,000,000	9,100,000
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	3,000,000	$ 9,100,000
California [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Surety bonds and standby letters of credit	84,800,000
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