Quarterly report pursuant to Section 13 or 15(d)

Workers' Compensation Claims - Additional Information (Detail)

v3.10.0.1
Workers' Compensation Claims - Additional Information (Detail) - USD ($)
9 Months Ended 12 Months Ended
Jul. 01, 2018
Sep. 30, 2018
Dec. 31, 2017
Jun. 30, 2018
Sep. 30, 2017
Jun. 30, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Worker's compensation risk claim maximum $ 5,000,000 $ 5,000,000          
Balance in Chubb trust accounts   430,000,000 $ 380,600,000        
Surety bonds 30,000,000            
Specified investment balances or other financial instruments   85,200,000 96,800,000        
Surety bonds and standby letters of credit   85,200,000          
Estimated future liability for unsettled workers' compensation   398,838,000 363,517,000 $ 390,814,000 $ 344,685,000 $ 330,079,000 $ 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          
Wells Fargo Bank, National Association [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Letter of credit $ 63,700,000            
Chubb Limited [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Worker's compensation risk claim maximum   $ 5,000,000