Workers' Compensation Expense (Schedule of Amounts Recognized in Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accrued Workers' Compensation [Line Items]
Total obligations	$ 194,347	$ 203,617
Less amount included in accrued expenses	20,044	18,782
Noncurrent obligations	174,303	184,835
Occupational disease costs
Accrued Workers' Compensation [Line Items]
Occupational disease costs	118,900	122,426	$ 111,159
Traumatic and other workers’ compensation claims
Accrued Workers' Compensation [Line Items]
Occupational disease costs	$ 75,447	$ 81,191