Accounting Policies (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Oct. 01, 2010
Health Insurance Costs [Abstract]
Number of days in advance of the beginning of a reporting quarter United establishes cash funding rates	90 days
Required accumulated cash surplus	$ 9,000		$ 9,000
Required deposit equal to approximately one day of claims funding activity	3,500
Amount which plan costs were less than the net premiums paid and owed	15,000
Prepaid health insurance, current	6,000
Premiums owed to United	$ 2,600
Workers' Compensation Costs [Abstract]
Company's maximum economic burden for the first layer of claims per occurrence				$ 1,000
Decrease Increase in accrued workers' compensation costs for changes in estimated losses		$ 2,000
Company's maximum aggregate economic burden for claims in excess of 1 million per policy year				$ 5,000
U.S. Treasury rates that correspond with the weighted average estimated claim payout period (in hundredths)	1.00%	1.00%
Incurred but not paid workers compensation liabilities [Abstract]
Beginning balance, January 1,	$ 136,088	$ 120,833
Accrued claims	32,720	25,041
Present value discount	(1,189)	(898)
Paid claims	(19,794)	(18,572)
Ending balance	147,825	126,404
Current portion of accrued claims	48,887	53,441
Long-term portion of accrued claims	98,938	72,963	92,048
Workers compensation administrative fees accrued	2,000
Undiscounted accrued workers' compensation costs	$ 157,400	$ 136,300
Time period incurred claims expected to be paid recorded as restricted cash	1 year
Time period incurred claims expected to be paid, included in deposits, a long-term asset	Greater than 1 year
Return of Excess Claim Funds Net of Additional Amounts Paid in Claim Funds for Prior Policy Years	$ 5,300
Restricted cash - worker's compensation	48,887		44,040
Deposits workers compensation	$ 110,877		$ 113,934
Time period estimate of incurred claim costs to be paid included in short-term liabilities	1 year
Time period incurred claims expected to be paid, included in long-term liabilities	Greater than 1 year