Accounting Policies (Details) (USD $)	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Dec. 31, 2010	Oct. 01, 2010	Sep. 30, 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	2,840,000		2,640,000
Amount which plan costs were less than the net premiums paid and owed	17,300,000
Prepaid health insurance, current	8,300,000
Premiums owed to United	6,300,000
Workers' Compensation Costs [Abstract]
Company's maximum economic burden for the first layer of claims per occurrence				1,000,000		1,000,000
Company's maximum aggregate economic burden for claims in excess of 1 million per policy year			5,000,000	5,000,000	5,000,000
Reduction in accrued workers' compensation costs for changes in estimated losses	6,700,000	4,000,000
U.S. Treasury rates that correspond with the weighted average estimated claim payout period (in hundredths)	0.80%	1.30%
Incurred but not paid workers' compensation liabilities [Abstract]
Beginning balance, January 1,	104,791,000	96,934,000
Accrued claims	19,164,000	19,523,000
Present value discount	(532,000)	(898,000)
Paid claims	(15,179,000)	(14,493,000)
Ending balance	108,244,000	101,066,000
Current portion of accrued claims	44,580,000	41,331,000
Long-term portion of accrued claims	63,664,000	59,735,000	60,054,000
Ending balance	108,244,000	101,066,000
Return of excess claims funds related to ACE program	2,500,000		9,600,000
Workers' compensation administrative fees accrued	700,000
Undiscounted accrued workers' compensation costs	120,900,000	115,200,000
Restricted cash - workers' compensation	44,580,000		44,737,000
Deposits - workers' compensation	$ 56,377,000		$ 52,320,000
Time period incurred claims expected to be paid recorded as restricted cash (in years)	1	1
Time period incurred claims expected to be paid, included in deposits, a long-term assets (in years)	Greater than 1Y	Greater than 1Y
Time period estimate of incurred claim costs to be paid included in short-term liabilities (in years)	1
Time period estimate of incurred claim costs to be paid included in long-term liabilities	Greater than 1Y