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Intangible assets - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Goodwill and Intangible Assets Disclosure [Abstract]        
Amortization of intangible assets $ 15.1 $ 15.0 $ 30.0 $ 29.8
Weighted average amortization period     12 years 3 months 18 days