Workers' Compensation Expense (Schedule of Amounts Recognized in Balance Sheet) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Accrued Workers' Compensation [Line Items]
Total obligations	$ 90,496	$ 92,000
Less amount included in accrued expenses	12,434	10,371
Noncurrent obligations	78,062	81,629
Occupational Disease [Member]
Accrued Workers' Compensation [Line Items]
Occupational disease costs	55,228	58,431
Workers' Compensation [Member]
Accrued Workers' Compensation [Line Items]
Occupational disease costs	$ 35,268	$ 33,569