Income taxes (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Feb. 25, 2021 subsidiary
Segment Reporting Information [Line Items]
Number of operating subsidiaries | subsidiary						1
Income tax expense	$ 9,600,000	$ 3,300,000	$ 19,400,000	$ 3,700,000
Pre-tax income (loss)	$ 79,700,000	$ 127,300,000	$ 221,900,000	$ (55,900,000)
Effective tax rate	12.00%		8.70%
Provision for taxes related to BEAT or GILTI			$ 0		$ 0
Net deferred tax asset	$ 26,100,000		26,100,000
Unrecognized Tax Benefits	3,200,000		3,200,000
Unrecognized tax benefits that would impact the effective tax rate	2,500,000		2,500,000
Unrecognized tax benefits that would not impact the effective tax rate	700,000		700,000
U.S.
Segment Reporting Information [Line Items]
Net deferred tax asset	70,100,000		70,100,000
Luxembourg
Segment Reporting Information [Line Items]
Net deferred tax asset	148,700,000		148,700,000
UK
Segment Reporting Information [Line Items]
Net deferred tax liabilities	5,100,000		5,100,000
Sweden
Segment Reporting Information [Line Items]
Net deferred tax liabilities	178,000,000.0		178,000,000.0
Other
Segment Reporting Information [Line Items]
Net deferred tax liabilities	$ 9,600,000		$ 9,600,000