Restrictions on cash and investments (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Restricted Cash and Cash Equivalents Items [Line Items]
Investments restricted for statutory reserve funds	$ 2.0
Investments In Debt And Equity Securities
Restricted Cash and Cash Equivalents Items [Line Items]
Investments restricted for statutory reserve funds	544.0	$ 523.5
Cash and Cash Equivalents
Restricted Cash and Cash Equivalents Items [Line Items]
Investments restricted for statutory reserve funds	$ 8.6	$ 41.4