Income taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Non-Bermuda pre-tax income (loss)	$ (133,500,000)	$ 38,300,000	$ 3,300,000
Provision for taxes related to BEAT and GILTI	0	0
Net deferred tax assets	86,600,000	400,000	8,300,000
Valuation allowance	113,300,000	0	0
Unrecognized tax benefits	10,700,000	1,600,000	1,500,000
Unrecognized tax benefits that would impact the effective tax rate	9,700,000
Unrecognized tax benefits that would not impact the effective tax rate	300,000
Interest expense on unrecognized tax benefits	100,000	0	0
Accrued interest on unrecognized tax benefits	700,000	500,000
Alternative minimum tax carryforwards
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	100,000
U.S.
Operating Loss Carryforwards [Line Items]
Non-Bermuda pre-tax income (loss)	21,800,000	38,100,000	3,200,000
Net deferred tax assets	53,500,000
Valuation allowance	13,400,000
U.S. | Foreign tax credits carryforwards
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	17,000,000
U.S. | Expire in 2022 | Foreign tax credits carryforwards
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	9,500,000
U.S. | Foreign
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards subject to annual limitation under IRS Code Section 382	133,600,000
Operating loss carryforwards subject to annual limitation under IRS Code Section 382 and SRLY provisions	11,000,000
U.S. | Foreign | Expiring between 2022 and 2025
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards subject to annual limitation under IRS Code Section 382	4,700,000
U.S. | Foreign | Expire between 2031 and 2039
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards subject to annual limitation under IRS Code Section 382	107,800,000
U.S. | Foreign | Do not expire
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards subject to annual limitation under IRS Code Section 382	21,100,000
Luxembourg
Operating Loss Carryforwards [Line Items]
Non-Bermuda pre-tax income (loss)	(20,500,000)	0	0
Net deferred tax assets	128,500,000
Valuation allowance	62,100,000
Luxembourg | Foreign
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	521,600,000
U.K.
Operating Loss Carryforwards [Line Items]
Non-Bermuda pre-tax income (loss)	1,900,000	200,000	100,000
Net deferred tax liabilities	5,200,000
Valuation allowance	37,800,000
Sweden
Operating Loss Carryforwards [Line Items]
Non-Bermuda pre-tax income (loss)	(138,100,000)	0	0
Net deferred tax liabilities	90,900,000
Sweden | Foreign tax credits carryforwards
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	9,100,000
Other
Operating Loss Carryforwards [Line Items]
Non-Bermuda pre-tax income (loss)	1,500,000	$ 0	$ 0
Net deferred tax assets	$ 700,000