Debt and Other Obligations - Other Short-Term Debt and Obligations (Details)	Dec. 31, 2025 USD ($)	Dec. 31, 2025 EUR (€)	Sep. 30, 2025 EUR (€)	Dec. 31, 2024 USD ($)	Dec. 31, 2024 EUR (€)	Oct. 31, 2023 EUR (€)	Sep. 30, 2023 EUR (€)	May 31, 2022 EUR (€)	Dec. 31, 2014 EUR (€)
Debt Instrument [Line Items]
Repurchase Agreement	$ 43,000,000.0			$ 36,500,000
Total of Other Short-term Debt and Obligations	289,800,000			250,900,000
Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Outstanding	58,800,000			0
Borrowing capacity	411,000,000	€ 350,000,000	€ 350,000,000			€ 300,000,000	€ 350,000,000	€ 350,000,000	€ 115,000,000
Revolving Credit Facility | Ancillary Credit Facilities
Debt Instrument [Line Items]
Borrowing capacity	275,000,000.0	€ 234,000,000		243,100,000	€ 234,000,000.0
Revolving Credit Facility | Ancillary Credit Facilities | OEC GmbH outstanding borrowings
Debt Instrument [Line Items]
Outstanding	127,900,000			147,800,000
Revolving Credit Facility | Ancillary Credit Facilities | OEC LLC outstanding borrowings
Debt Instrument [Line Items]
Outstanding	19,400,000			14,000,000.0
Revolving Credit Facility | Ancillary Credit Facilities | OEC Huaibei outstanding borrowings
Debt Instrument [Line Items]
Outstanding	4,600,000			16,500,000
Working Capital Loan | South Korea
Debt Instrument [Line Items]
Borrowing capacity	39,800,000
Working Capital Loan | Uncommitted | South Korea
Debt Instrument [Line Items]
Outstanding	1,700,000			1,700,000
Working Capital Loan | Committed | South Korea
Debt Instrument [Line Items]
Outstanding	17,300,000			22,700,000
Working Capital Loan | China Working Capital Loans | China
Debt Instrument [Line Items]
Outstanding	$ 17,100,000			$ 11,700,000