Reserve for Claims and Claim Expenses - Prior Year Development of the Reserve for Net Claims and Claim Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	$ (450,607)	$ (247,582)	$ (249,470)
Actuarial assumption changes
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years		23,847
Property
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(408,905)	(205,741)	(233,373)
Property | Actuarial assumption changes
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	840		5,450
Property | Large and small catastrophe events and attritional loss movements
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years		(229,588)	(238,823)
Property | Large catastrophe events
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(309,820)	(198,564)	(204,072)
Property | 2022 Weather-Related Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(85,653)
Property | 2021 Weather-Related Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(36,949)	(12,387)
Property | 2020 Weather-Related Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(42,577)	(24,589)	17,140
Property | 2019 Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(43,850)	(97,034)	(61,634)
Property | 2018 Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(40,050)	(20,318)	(101,096)
Property | 2017 Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(46,404)	(39,481)	(49,090)
Property | Other
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(14,337)	(4,755)	(9,392)
Property | Small catastrophe events and attritional loss movements
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years		(31,024)	(34,751)
Property | Other small catastrophe events and attritional loss movements
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(99,925)	(31,024)	(34,751)
Property | Operating Segments
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(408,905)	(205,741)	(233,373)
Casualty and Specialty
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(41,702)	(41,841)	(16,097)
Casualty and Specialty | Actuarial methods - actual reported claims less than expected claims
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(44,612)	(63,353)	(19,078)
Casualty and Specialty | Actuarial assumption changes
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	2,910	21,512	2,981
Casualty and Specialty | Operating Segments
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	$ (41,702)	$ (41,841)	$ (16,097)