Quarterly report pursuant to Section 13 or 15(d)

Workers' Compensation Claims - Additional Information (Detail)

v3.20.2
Workers' Compensation Claims - Additional Information (Detail) - USD ($)
9 Months Ended 12 Months Ended
Sep. 30, 2020
Dec. 31, 2019
Jun. 30, 2020
Jun. 29, 2020
Sep. 30, 2019
Jun. 30, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Worker's compensation risk claim maximum $ 3,000,000.0            
Balance in Chubb trust accounts 277,400,000 $ 393,500,000   $ 115,700,000      
Collateral securities maintain to cover potential workers compensation claims losses 59,700,000 76,100,000          
Surety bonds and standby letters of credit 59,700,000            
Claim payments receivable from Chubb     $ 700,000        
Estimated future liability for unsettled workers' compensation 347,348,000 438,986,000 $ 336,504,000   $ 430,046,000 $ 430,736,000 $ 413,397,000
Reserves incurred in excess of retention limits 4,800,000 3,300,000          
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 4,800,000 $ 3,300,000          
Wells Fargo Bank, National Association [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Letter of credit 63,700,000            
Maryland [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Reinsurance coverage 1,000,000.0            
Colorado [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Reinsurance coverage 2,000,000.0            
California [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Surety bonds and standby letters of credit $ 39,200,000