Workers' Compensation Claims - Summarizes Aggregate Workers' Compensation Reserve Activity (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Workers Compensation Reserve [Abstract]
Workers' compensation claims liabilities, Beginning balance	$ 362,663	$ 445,310	$ 357,746	$ 438,986
Add: claims expense accrual
Current period	35,743	32,729	69,013	71,221
Prior periods	(5,483)	(1,373)	(6,663)	(2,186)
Total expense accrual	30,260	31,356	62,350	69,035
Less: claim payments related to
Current period	3,927	4,527	4,979	6,077
Prior periods	73,240	135,853	99,005	165,530
Total paid	77,167	140,380	103,984	171,607
Change in claims incurred in excess of retention limits	(23)	218	(379)	90
Workers' compensation claims liabilities, Ending balance	315,733	336,504	315,733	336,504
Incurred but not reported (IBNR)	$ 190,818	$ 206,521	$ 190,818	$ 206,521
Ratio of IBNR to workers' compensation claims liabilities	60.00%	61.00%	60.00%	61.00%