Workers' Compensation Claims - Summarizes Aggregate Workers' Compensation Reserve Activity (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Workers Compensation Reserve [Abstract]
Workers' compensation claims liabilities, Beginning balance	$ 438,986	$ 413,397
Add: claims expense accrual
Current period	38,492	40,385
Prior periods	(813)	(1,700)
Total expense accrual	37,679	38,685
Less: claim payments related to
Current period	1,550	1,459
Prior periods	29,677	27,716
Total paid	31,227	29,175
Change in claims incurred in excess of retention limits	(128)	(35)
Workers' compensation claims liabilities, Ending balance	445,310	422,872
Incurred but not reported (IBNR)	$ 282,497	$ 268,291
Ratio of IBNR to workers' compensation claims liabilities	63.00%	63.00%