Taxation - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Increase (decrease) in valuation allowance	$ 62,100,000	$ 42,800,000	$ 13,000,000
Unrealized losses in the US investment portfolio	320,900,000
Income taxes paid (refunded)	3,129,000	(4,261,000)	$ 5,668,000
Unrecognized tax benefits	0	0
Interest and penalties accrued on unrecognized tax benefits	$ 0	$ 0
U.S.
Operating Loss Carryforwards [Line Items]
Expected tax rate	5.00%
Foreign statutory income tax rate	21.00%
Operating loss carryforwards	$ 310,400,000
Bermuda
Operating Loss Carryforwards [Line Items]
Statutory income tax rate	0.00%
Ireland
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate	12.50%
Operating loss carryforwards	$ 7,700,000
U.K.
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate	19.00%
Operating loss carryforwards	$ 263,900,000
Singapore
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate	17.00%
Operating loss carryforwards	$ 18,700,000
Switzerland
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate	19.70%
Operating loss carryforwards	$ 527,200,000
Australia
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate	30.00%
Operating loss carryforwards	$ 7,500,000