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Summary of Accounting Policies (Accounts Receivable and Allowance for Doubtful Accounts) (Details) - Sales revenue, goods, net - Customer concentration risk - customer
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Concentration Risk [Line Items]      
Largest customers (in number of customers) 15 15 15
Largest customers as a percentage of sales 29.00% 33.00% 31.00%