Workers' Compensation Expense (Schedule of Amounts Recognized in Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accrued Workers' Compensation [Line Items]
Total obligations	$ 129,145	$ 111,005
Less amount included in accrued expenses	16,875	16,714
Noncurrent obligations	112,270	94,291
Occupational Disease [Member]
Accrued Workers' Compensation [Line Items]
Occupational disease costs	90,836	72,749
Workers' Compensation [Member]
Accrued Workers' Compensation [Line Items]
Occupational disease costs	$ 38,309	$ 38,256