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General Information - Additional Information (Detail) € / shares in Units, $ / shares in Units, € in Thousands, $ in Millions |  |  | 6 Months Ended |  |
--- | --- | --- | --- | --- | ---
Feb. 15, 2018 EUR (€) | Feb. 15, 2018 USD ($) | Feb. 13, 2018 € / shares $ / shares shares | Jun. 30, 2019 EUR (€) | Jun. 30, 2018 EUR (€) | Dec. 31, 2018 EUR (€) | Dec. 31, 2017 EUR (€)
Disclosure of general information [line items] |  |  |  |  |  |  |
Accumulated loss |  |  |  | € (190,100) |  |  |
Cash and cash equivalents |  |  |  | 131,993 | € 170,327 | € 143,747 | € 149,678
Investments |  |  |  | 47,879 |  | € 61,800 |
Aggregate purchase price |  |  |  | € 1 | € 44,731 |  |
Investors [member] |  |  |  |  |  |  |
Disclosure of general information [line items] |  |  |  |  |  |  |
Common shares issued | shares |  |  | 3,099,997 |  |  |  |
Issue price per share | € / shares |  |  | € 0.09 |  |  |  |
Aggregate purchase price | € 44,800 | $ 55.8 |  |  |  |  |
Purchase price | $ / shares |  |  | € 18.0 |  |  |  |

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- Definition The amount of cash on hand and demand deposits, along with short-term, highly liquid investments that are readily convertible to known amounts of cash and that are subject to an insignificant risk of changes in value. [Refer: Cash; Cash equivalents] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 7 -IssueDate 2018-01-01 -Paragraph 45 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2018-03-01&anchor=para_45&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2018-01-01 -Paragraph B13 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2018-03-01&anchor=para_B13_a&doctype=Appendix&seq=2 -URIDate 2018-03-16 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 54 -Subparagraph i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_54_i&doctype=Standard -URIDate 2018-03-16 + Details
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