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Segment reporting - Revenue from external customers by products and services (Details) $ in Thousands | 3 Months Ended | 5 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Dec. 31, 2017 USD ($) | Sep. 30, 2017 USD ($) | Jun. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Sep. 30, 2016 USD ($) | Jun. 30, 2016 USD ($) | Mar. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Jun. 30, 2018 USD ($) | Jun. 30, 2017 USD ($) | Dec. 31, 2017 USD ($) segment | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Reportable Segments | segment |  |  |  |  |  |  |  |  |  |  |  | 2 |  |
Revenue, Net | $ 192,473 | $ 137,245 | $ 116,314 | $ 104,739 | $ 115,432 | $ 111,590 | $ 115,365 | $ 95,576 | $ 193,133 | $ 908,231 | $ 221,053 | $ 550,771 | $ 437,963 | $ 533,040
U.S. |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue, Net |  |  |  |  |  |  |  |  |  |  |  | 103,890 | 74,526 | 107,517
Americas |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue, Net |  |  |  |  |  |  |  |  |  |  |  | 129,103 | 116,944 | 132,917
Asia Pacific |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue, Net |  |  |  |  |  |  |  |  |  |  |  | 46,329 | 41,302 | 37,509
Europe, Middle East, Africa |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue, Net |  |  |  |  |  |  |  |  |  |  |  | $ 271,449 | $ 205,191 | $ 255,097

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References No definition available. + Details
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- Definition Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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