The average exchange rate used by the entity. Exchange rate is the ratio of exchange for two currencies.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition

The spot exchange rate at the end of the reporting period. Exchange rate is the ratio of exchange for two currencies. Spot exchange rate is the exchange rate for immediate delivery.

+ References

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- Definition

The amount of an expected dividend used to calculate the fair value of share options granted.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- References

No definition available.

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n/a

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No definition available.

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Summary of significant accounting policies - Foreign currencies (Details) € in Thousands		12 Months Ended
	Apr. 07, 2017 EUR (€)	Dec. 31, 2020 $ / €	Dec. 31, 2020 $ / € ₨ / €	Dec. 31, 2020 $ / € £ / €	Dec. 31, 2020 $ / € ¥ / €	Dec. 31, 2019 $ / €	Dec. 31, 2019 $ / € ₨ / €	Dec. 31, 2019 $ / € £ / €	Dec. 31, 2019 $ / € ¥ / €	Dec. 31, 2018 $ / €	Dec. 31, 2018 ₨ / €	Dec. 31, 2018 £ / €	Dec. 31, 2018 ¥ / €	Dec. 31, 2020 ₨ / €	Dec. 31, 2020 £ / €	Dec. 31, 2020 ¥ / €	Dec. 31, 2019 ₨ / €	Dec. 31, 2019 £ / €	Dec. 31, 2019 ¥ / €
Summary of significant accounting policies
Expected dividends	€ 0
Foreign exchange rates
Average foreign exchange rate		1.1422	84.6392	0.8897	7.8747	1.1195	78.8361	0.8778	7.7355	1.1810	80.7332	0.8847	7.8081
Closing foreign exchange rate		1.2271	1.2271	1.2271	1.2271	1.1234	1.1234	1.1234	1.1234					89.6605	0.8990	8.0225	80.1870	0.8508	7.8205