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Related parties - Narrative (Details) | Jun. 30, 2018 joint_venture
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Related Party [Abstract] |
Number of joint ventures accounted for using the equity method | 1

X
- Definition Number Of Joint Ventures, Related Party Transactions + References No definition available. + Details
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Namespace Prefix: | oec_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Related Party [Abstract] + References No definition available. + Details
Name: | oec_RelatedPartyAbstract
Namespace Prefix: | oec_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration