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Trade accounts receivable - net (Tables) | 12 Months Ended
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Dec. 31, 2017
Receivables [Abstract] |
Schedule of Accounts, Notes, Loans and Financing Receivable | The following table represents the activity occurring in the reserves for doubtful accounts in 2017, 2016 and 2015.
(in thousands) |  | Beginning Balance at January 1 |  | Net additions charged to Operations |  | Deductions and Other |  | Ending Balance at December 31 |
2017 |  | $ | 365 |  | $ | 136 |  | $ | 221 |  | $ | 722 |
2016 |  | $ | 335 |  | $ | 21 |  | $ | 9 |  | $ | 365 |
2015 |  | $ | 244 |  | $ | 99 |  | $ | (8) |  | $ | 335 |

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- Definition Tabular disclosure of the various types of trade accounts and notes receivable and for each the gross carrying value, allowance, and net carrying value as of the balance sheet date. Presentation is categorized by current, noncurrent and unclassified receivables. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3,4) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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