Accrued Workers' Compensation Accrued Workers' Compensation (Schedule of Changes in Projected Benefit Obligation) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligations at January 1	$ 54,184
Defined Benefit Plan, Curtailments	(1,770)
Benefit Obligations at December 31			17,412
Occupational Disease [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligations at December 31	58,431
Workers' Compensation [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	1,993	2,059	727
Interest cost	2,400	1,799	675
Actuarial Loss	(5,373)	7,081
Benefits Paid	(1,873)	(1,097)
Defined Benefit Plan, Curtailments	7,100
Acquisition of ICG		$ 26,930