Workers' Compensation - Summarizes Aggregate Workers' Compensation Reserve Activity (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Workers Compensation Reserve [Abstract]
Workers' compensation claims liabilities, Beginning balance	$ 120,135	$ 77,212	$ 112,444	$ 70,564
Add: claims expense accrual:
Current period	17,548	14,752	33,899	27,429
Prior periods	1,303	4,234	5,104	7,686
Total expense accrual	18,851	18,986	39,003	35,115
Less: claim payments related to:
Current period	2,739	2,448	3,138	2,874
Prior periods	13,741	9,207	25,803	18,262
Total paid	16,480	11,655	28,941	21,136
Workers' compensation claims liabilities, Ending balance	122,506	84,543	122,506	84,543
Incurred but not reported (IBNR)	$ 29,871	$ 56,434	$ 29,871	$ 56,434