Self-Insurance Accruals (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Self-Insurance Accruals [Abstract]
Workers' compensation			$ 38,811	$ 35,304
Present value discount			2,236	1,937
Workers' compensation, net of discount			36,575	33,367
Vehicle liability			4,763	5,880
General liability			21,500	21,092
Total	$ 60,339	$ 58,893	62,838	60,339
Less current portion			23,092	22,553
Noncurrent portion			$ 39,746	$ 37,786
Loss contingency accrual [Roll Forward]
Balance, beginning of year	60,339	58,893
Provision for claims	33,404	33,499
Payment of claims	30,905	32,053
Balance, end of year	$ 62,838	$ 60,339
Workers' compensation discount rate	2.20%	2.20%