Taxation - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Loss Carryforwards [Line Items]
Deferred tax asset, increase (decrease), net, amount	$ 593,800,000
Deferred tax asset, utilization period	10 years
Increase (decrease) in valuation allowance		$ 19,600,000	$ 62,100,000	$ 42,800,000
Unrealized losses in the US investment portfolio		186,200,000
Income taxes paid (refunded)		26,777,000	3,129,000	$ (4,261,000)
Unrecognized tax benefits	$ 0	0	0
Interest and penalties accrued on unrecognized tax benefits	0	$ 0	$ 0
Bermuda
Operating Loss Carryforwards [Line Items]
Statutory income tax rate		0.00%
U.S.
Operating Loss Carryforwards [Line Items]
Expected tax rate		5.00%
Foreign statutory income tax rate		21.00%
U.S. | 2037
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	167,000,000	$ 167,000,000
U.S. | 2027
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	105,700,000	$ 105,700,000
Ireland
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		12.50%
Operating loss carryforwards	7,800,000	$ 7,800,000
U.K.
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		23.50%
Operating loss carryforwards	185,600,000	$ 185,600,000
Singapore
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		17.00%
Operating loss carryforwards	5,600,000	$ 5,600,000
Switzerland
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		19.70%
Switzerland | 2024
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	570,900,000	$ 570,900,000
Luxembourg
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		24.90%
Operating loss carryforwards	$ 155,700,000	$ 155,700,000
Canada
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		15.00%
Australia
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		30.00%