Quarterly report pursuant to Section 13 or 15(d)

Workers' Compensation Claims - Additional Information (Detail)

v3.8.0.1
Workers' Compensation Claims - Additional Information (Detail) - USD ($)
9 Months Ended 12 Months Ended
Sep. 30, 2017
Dec. 31, 2016
Jun. 30, 2017
Sep. 30, 2016
Jun. 30, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Balance in Chubb trust account $ 358,400,000 $ 277,100,000        
Specified investment balances or other financial instruments 97,000,000 135,000,000        
Surety bonds and standby letters of credit 97,000,000          
Estimated future liability for unsettled workers' compensation 344,685,000 312,537,000 $ 330,079,000 $ 291,931,000 $ 277,050,000 $ 255,675,000
Reserves incurred in excess of retention limits 3,100,000 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 3,100,000 $ 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