Annual report pursuant to Section 13 and 15(d)

Commitments and Contingencies (Schedule of Rent Expense) (Details)

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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