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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.

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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.

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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

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