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Accounts receivable (Tables) | 12 Months Ended
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Dec. 31, 2017
Accounts receivable [Abstract] |
Accounts receivable | Accounts receivable consist of the following:
| December 31, |
(in thousands) | 2017 |  | 2016 |
Billed |  | $ | 118,918 |  |  | $ | 90,439 |
Unbilled |  |  | 24,735 |  |  |  | 48,039 |
Total |  | $ | 143,653 |  |  | $ | 138,478 |

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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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