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Description of the business and recent developments: Financial instruments (Details) - Dec. 31, 2021 € in Millions, $ in Millions	USD ($)	EUR (€)
Level 2 \| Interest Rate Swap
Financial instruments
Fair value of interest rate swaps	$ 9.0
Senior unsecured 2024 Notes
Financial instruments
Senior notes	397.0	€ 350.0
Senior unsecured 2024 Notes \| Level 2
Financial instruments
Senior notes, fair value	402.0
2021 Notes
Financial instruments
Senior notes	500.0
2021 Notes \| Level 2
Financial instruments
Senior notes, fair value	$ 508.1