Workers' Compensation Expense (Worker's Compensation Expense) (Details) - Workers' Compensation [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accrued Workers' Compensation [Line Items]
Total net benefit	$ 15,199	$ 4,432	$ 6,137
Traumatic injury claims and assessments	16,781	19,924	21,089
Total workers’ compensation expense	31,980	$ 24,356	$ 27,226
Surety bonds and letters of credit outstanding	$ 148,200