Accounting Policies (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Health Insurance Costs [Abstract]
Number of days in advance of the beginning of a reporting quarter United establishes cash funding rates (in days)	90
Required accumulated cash surplus	$ 9,000,000
Required deposit equal to approximately one day of claims funding activity	2,840,000		2,640,000
Amount which Plan Costs were less than the net premiums paid and owed	28,900,000
Prepaid health insurance, current	19,900,000
Premiums owed to United	5,800,000
Workers' Compensation Costs [Abstract]
Company's maximum economic burden for the first layer of claims per occurrence	1,000,000
Company's maximum aggregate economic burden for claims per policy year	5,000,000
Reduction in accrued workers' compensation costs for changes in estimated losses	3,500,000	1,900,000
U.S. Treasury rates that correspond with the weighted average estimated claim payout period (in hundredths)	1.00%	1.50%
Incurred but not paid workers' compensation liabilities [Abstract]
Beginning balance	104,791,000	96,934,000
Accrued claims	9,495,000	9,790,000
Present value discount	(347,000)	(530,000)
Paid claims	(6,976,000)	(7,533,000)
Ending balance	106,963,000	98,661,000
Current portion of accrued claims	45,068,000	40,807,000
Long-term portion of accrued claims	61,895,000	57,854,000	60,054,000
Ending balance	106,963,000	98,661,000
Workers' compensation administrative fees accrued	2,000,000
Undiscounted accrued workers' compensation costs	120,100,000	113,100,000
Restricted cash - workers' compensation	45,068,000		44,737,000
Deposits - workers' compensation	$ 55,665,000		$ 52,320,000
Time period incurred claims expected to be paid recorded as restricted (in years)	1Y
Time period incurred claims expected to be paid included in deposits	Greater than 1Y
Time period estimate of incurred claim costs to be paid included in short-term liabilities	1Y
Time period estimate of incurred claim costs to be paid included in long-term liabilities	Greater than 1Y