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, 2022	Dec. 31, 2021	Dec. 31, 2020
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	$ (247,582)	$ (249,470)	$ (183,812)
Actuarial assumption changes
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years		5,450
Property
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(205,741)	(233,373)	(157,049)
Property | Actuarial assumption changes
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	23,847		5,445
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)	(162,494)
Property | Large catastrophe events
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(198,564)	(204,072)	(120,905)
Property | 2021 Weather-Related Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(12,387)
Property | 2020 Weather-Related Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(24,589)	17,140
Property | 2019 Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(97,034)	(61,634)	(44,389)
Property | 2018 Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(20,318)	(101,096)	(43,991)
Property | 2017 Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(39,481)	(49,090)	(32,649)
Property | Other
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(4,755)	(9,392)	124
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)	(41,589)
Property | Other 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)	(41,589)
Property | Operating Segments
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(205,741)	(233,373)	(157,049)
Casualty and Specialty
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	(41,841)	(16,097)	(26,763)
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	(63,353)	(19,078)	(29,280)
Casualty and Specialty | Actuarial assumption changes
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	21,512	2,981	2,517
Casualty and Specialty | Operating Segments
Liability for Catastrophe Claims [Line Items]
Net claims and claim expenses incurred – prior accident years	$ (41,841)	$ (16,097)	$ (26,763)