Accounting Policies (Details) (USD $)	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
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	2,640,000		2,640,000
Amount which Plan Costs were less than the net premiums paid and owed	22,700,000
Prepaid health insurance, current	13,700,000
Premiums owed to United	1,900,000
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 in excess of $1 million per policy year	5,000,000
Reduction in accrued workers' compensation costs for changes in estimated losses	8,600,000	5,000,000
U.S. Treasury rates that correspond with the weighted average estimated claim payout period (in hundredths)	1.20%	1.50%
Incurred but not paid workers' compensation liabilities [Abstract]
Beginning balance	96,934,000	88,450,000
Accrued claims	26,668,000	24,985,000
Present value discount	(1,159,000)	(1,350,000)
Paid claims	(21,123,000)	(18,133,000)
Ending balance	101,320,000	93,952,000
Current portion of accrued claims	42,812,000	39,661,000
Long-term portion of accrued claims	58,508,000	54,291,000	55,730,000
Ending balance	101,320,000	93,952,000
Workers' compensation administrative fees accrued	2,500,000
Excess claim funds related to the ACE Program	10,000,000	15,600,000
Restricted cash - workers' compensation	42,812,000		41,204,000
Deposits - workers' compensation	$ 46,728,000		$ 51,731,000