Workers' Compensation Claims - Summarizes Aggregate Workers' Compensation Reserve Activity (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Workers Compensation Reserve [Abstract]
Workers' compensation claims liabilities, Beginning balance	$ 255,675	$ 225,278	$ 121,056
Add: claims expense accrual
Current year	137,852	122,740	104,314
Prior years	(301)	(13,683)	66,719
Total expense accrual	137,551	109,057	171,033
Less: claims payments related to
Current year	20,180	17,517	15,243
Prior years	69,626	61,143	51,568
Total paid	89,806	78,660	66,811
Add: claims incurred in excess of retention limits	9,117
Workers' compensation claims liabilities, Ending balance	312,537	255,675	225,278
Incurred but not reported (IBNR)	$ 158,169	$ 127,792	$ 113,984