| **Receivables and Allowance for Doubtful Receivables (Tables)** | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
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| **Receivables [Abstract]**                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| Schedule of Accounts, Notes, Loans and Financing Receivable     | Changes in the allowance for doubtful receivables during the years ended December 31, 2013, 2012 and 2011 are summarized below (amounts in thousands):   Additions Deductions  DescriptionBalance at beginning of year Charged to costs and expenses Charged to other accounts Write-offs net of recoveries Balance at end of yearDecember 31, 2013$3,215 2,370 (446) 2,793 2,346December 31, 2012$5,796 3,649 (2,261) 3,969 3,215December 31, 2011$9,189 4,294 (29) 7,658 5,796Receivables consist of the following at December 31, 2013 and 2012 (amounts in thousands): 2013 2012Trade$225,689 148,902Employee1,037 703Other1,646 831Total receivables$228,372 150,436 |

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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=d3e13212-122682Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3, 4 -Article 5
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