Commitments and Contingencies (Schedule of Rent Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Rent expense	$ 86,121	$ 77,083	$ 69,570
Selling, General and Administrative Expense [Member]
Property, Plant and Equipment [Line Items]
Rent expense	84,564	75,457	67,881
Cost of Sales [Member]
Property, Plant and Equipment [Line Items]
Rent expense	$ 1,557	$ 1,626	$ 1,689