Workers' Compensation Expense (Worker's Compensation Expense) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Defined Benefit Plan Disclosure [Line Items]
Curtailments	$ (2,200)		$ (1,770)
Workers' Compensation [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	419	807	1,458	1,246
Interest cost	629	619	1,708	1,177
Net amortization		(109)	(574)	(370)
Curtailments			1,933
Net benefit cost (credit)	1,048	1,317	4,525	2,053
Traumatic injury claims and assessments	7,453	5,207	19,052	10,856
Total workers' compensation expense	$ 8,501	$ 6,524	$ 23,577	$ 12,909