Self-Insurance Accruals (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Rate	Dec. 31, 2011 Rate
Self-Insurance Accruals [Abstract]
Workers' compensation	$ 40,450	$ 33,355
Present value discount	2,003	1,756
Workers' compensation, net of discount	38,447	31,599
Vehicle liability	5,117	6,544
General liability	18,169	19,122
Total	61,733	57,265
Less current portion	20,115	26,793
Noncurrent portion	41,618	30,472
Loss Contingency Accrual [Roll Forward]
Balance, beginning of year	57,265	54,410
Provision for claims	29,590	29,931
Payment of claims	25,122	27,076
Balance, end of year	$ 61,733	$ 57,265
Workers' compensation discount rate	1.90%	2.50%