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Non-controlling interests - Additional Information (Detail)			12 Months Ended
	Jul. 01, 2020 EUR (€) shares	Jun. 30, 2020 EUR (€)	Dec. 31, 2020 EUR (€) € / shares	Dec. 31, 2019 EUR (€)		Dec. 31, 2018 EUR (€)	Jul. 01, 2020 $ / shares
Statements [Line Items]
Par value per share | € / shares			€ 0.01
Ownership interests held by non-controlling interests		5.14%
Stock issued during period, value, new issues		€ 500,000	€ 0.01
Increase (decrease) through changes in noncontrolling interest		€ 500,000
Loss on non-controlling interest			600,000	€ 900,000		€ 900,000
Non-controlling interests			0	1,020,000	[1]	1,200,000
MD Anderson compensation expense			€ 45,000	€ 700,000		€ 1,360,000
Restricted Stock Acquisition Agreement [Member]
Statements [Line Items]
Stock issued during period, shares, acquisitions | shares	697,431
ARYA [Member]
Statements [Line Items]
Par value per share | $ / shares							$ 15.15
Increase (decrease) through changes in noncontrolling interest	€ 500,000
MD Anderson [Member]
Statements [Line Items]
Number of shares exchanged in subsidiaries | shares	379,420
[1] See Note 2 for details regarding the change in presentation of Other financial assets

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- Definition

The amount of equity in a subsidiary not attributable, directly or indirectly, to a parent. [Refer: Subsidiaries [member]]

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