Shareholders' Equity - Summary of Inputs Used in the Measurement of the Fair Values and the Related Fair Values at the Grant Dates (Detail)	6 Months Ended
Jun. 30, 2019 yr € / shares
Key management personnel [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Expected volatility (weighted-average)	87.58%
Contractual life \| yr	10
Expected dividends	0.00%
Key management personnel [member] \| Bottom of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Fair value at grant date	€ 6.07
Share price at grant date	9.83
Exercise price	€ 9.83
Expected dividends	0.00%
Risk-free interest rate (based on government bonds)	2.13%
Key management personnel [member] \| Top of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Fair value at grant date	€ 7.60
Share price at grant date	12.49
Exercise price	€ 12.49
Expected dividends	0.00%
Risk-free interest rate (based on government bonds)	2.74%
All other employees [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Expected volatility (weighted-average)	87.11%
Contractual life \| yr	10
Expected dividends	0.00%
All other employees [member] \| Bottom of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Fair value at grant date	€ 6.15
Share price at grant date	9.83
Exercise price	€ 9.83
Expected dividends	0.00%
Risk-free interest rate (based on government bonds)	2.02%
All other employees [member] \| Top of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Fair value at grant date	€ 8.62
Share price at grant date	14.19
Exercise price	€ 14.19
Expected dividends	0.00%
Risk-free interest rate (based on government bonds)	2.65%

The expected volatility of the share price used to calculate the fair value of the share options granted. Expected volatility is a measure of the amount by which a price is expected to fluctuate during a period. The measure of volatility used in option pricing models is the annualised standard deviation of the continuously compounded rates of return on the share over a period of time.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2018-01-01
-Paragraph 47
-Subparagraph a
-Clause i
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2018-03-01&anchor=para_47_a_i&doctype=Standard
-URIDate 2018-03-16

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- Definition

The option life of share options granted.

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The implied yield currently available on zero-coupon government issues of the country in whose currency the exercise price for share options granted is expressed, with a remaining term equal to the expected term of the option being valued (based on the option's remaining contractual life and taking into account the effects of expected early exercise). [Refer: Government [member]]

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Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

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- Definition

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

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- Definition

Employee option exercised price per share

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- Definition

Fair value assumptions grant date share price.

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- Definition

Share purchased price per share.

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