Annual report pursuant to Section 13 and 15(d)

Receivables and Allowance for Doubtful Receivables (Receivables by Type) (Details)

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Receivables and Allowance for Doubtful Receivables (Receivables by Type) (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Receivables $ 219,794 $ 208,384
Trade Accounts Receivable    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Receivables 218,491 205,645
Other Receivable    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Receivables $ 1,303 $ 2,739