Historical Loss and LAE Development - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
(Favorable)/Unfavorable Reserve Development
Prior accident years	$ (108,547)	$ (122,579)	$ (125,463)
Casualty Segment
(Favorable)/Unfavorable Reserve Development
Prior accident years	(78,498)	(87,225)	(108,632)
Casualty Segment | Commercial transportation
(Favorable)/Unfavorable Reserve Development
Prior accident years	(4,000)	(6,000)	(20,000)
Property segment
(Favorable)/Unfavorable Reserve Development
Prior accident years	(21,196)	(24,927)	(10,981)
Property segment | Marine
(Favorable)/Unfavorable Reserve Development
Prior accident years	(4,000)	(17,000)	(7,000)
Property segment | Commercial Property
(Favorable)/Unfavorable Reserve Development
Prior accident years	(11,000)		(2,000)
Property segment | Homeowners Property
(Favorable)/Unfavorable Reserve Development
Prior accident years		(2,000)
Surety Segment
(Favorable)/Unfavorable Reserve Development
Prior accident years	(8,853)	(10,427)	(5,850)
Surety Segment | Contract
(Favorable)/Unfavorable Reserve Development
Prior accident years	(3,000)	(5,000)	(5,000)
Surety Segment | Commercial
(Favorable)/Unfavorable Reserve Development
Prior accident years	(6,000)	(4,000)
Primary Occurrence | Casualty Segment | General liability
(Favorable)/Unfavorable Reserve Development
Prior accident years	(13,000)	(28,000)	(25,000)
Primary Occurrence | Casualty Segment | Small commercial
(Favorable)/Unfavorable Reserve Development
Prior accident years		(5,000)	(8,000)
Excess Occurrence | Casualty Segment | Commercial Products
(Favorable)/Unfavorable Reserve Development
Prior accident years	(15,000)	(6,000)	(11,000)
Excess Occurrence | Casualty Segment | Personal Umbrella
(Favorable)/Unfavorable Reserve Development
Prior accident years	(11,000)	(4,000)	(10,000)
Claims Made | Casualty Segment | Executive products
(Favorable)/Unfavorable Reserve Development
Prior accident years	(12,000)	(4,000)	(6,000)
Claims Made | Casualty Segment | Professional services
(Favorable)/Unfavorable Reserve Development
Prior accident years	$ (10,000)	$ (19,000)	$ (14,000)