Workers' Compensation Claims - Summarizes Aggregate Workers' Compensation Reserve Activity (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Workers Compensation Reserve [Abstract]
Workers' compensation claims liabilities, Beginning balance	$ 265,142	$ 231,723	$ 255,675	$ 225,279
Add: claims expense accrual:
Current period	34,627	30,748	65,781	58,530
Prior periods	(1,396)	(4,234)	(548)	(7,131)
Total expense accrual	33,231	26,514	65,233	51,399
Less: claim payments related to:
Current period	3,698	3,512	4,969	4,410
Prior periods	17,625	15,481	38,889	33,024
Total paid	21,323	18,993	43,858	37,434
Workers' compensation claims liabilities, Ending balance	277,050	239,244	277,050	239,244
Incurred but not reported (IBNR)	$ 140,115	$ 118,959	$ 140,115	$ 118,959