Workers' Compensation Claims - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Balance in Chubb trust account	$ 277,100,000	$ 166,600,000
Specified investment balances or other financial instruments	135,000,000	156,800,000
Surety bonds and standby letters of credit	128,800,000
Estimated future liability for unsettled workers' compensation	312,537,000	255,675,000	$ 225,278,000	$ 121,056,000
Reserves incurred in excess of retention limits	9,117,000
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	9,100,000	0
California [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Surety bonds and standby letters of credit	123,300,000
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
Ecole Insurance Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Surplus from wholly owned subsidiary	$ 12,100,000	$ 9,500,000