For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
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-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13531-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

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Significant Accounting Policies - Financial Instruments (Details)	12 Months Ended
	Dec. 31, 2019 EUR (€) financial_institution	Apr. 02, 2019 EUR (€)	Apr. 01, 2019 EUR (€)	May 05, 2017 EUR (€)	Jul. 25, 2014 EUR (€)
Revolving Credit Facility
Concentration Risk [Line Items]
Maximum borrowing capacity	€ 175,000,000.0	€ 250,000,000.0	€ 75,000,000.0	€ 175,000,000.0	€ 115,000,000.0
Number of financial institutions \| financial_institution	10
Maximum single commitment	€ 24,000,000.0
Ten Largest Customers \| Customer Concentration Risk \| Sales Revenue, Net
Concentration Risk [Line Items]
Concentration risk percentage	52.70%
Ten Largest Customers \| Customer Concentration Risk \| Sales Revenue, Net \| Rubber Carbon Black Segment
Concentration Risk [Line Items]
Concentration risk percentage	66.10%
Ten Largest Customers \| Customer Concentration Risk \| Sales Revenue, Net \| Specialty Carbon Black Segment
Concentration Risk [Line Items]
Concentration risk percentage	27.70%