Historical Loss and LAE Development - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
(Favorable)/Unfavorable Reserve Development
Prior accident years	$ (95,309)	$ (108,547)	$ (122,579)
Casualty Segment
(Favorable)/Unfavorable Reserve Development
Prior accident years	(52,878)	(78,498)	(87,225)
Casualty Segment | Commercial transportation
(Favorable)/Unfavorable Reserve Development
Prior accident years	8,000	(4,000)	(6,000)
Property segment
(Favorable)/Unfavorable Reserve Development
Prior accident years	(33,143)	(21,196)	(24,927)
Property segment | Marine
(Favorable)/Unfavorable Reserve Development
Prior accident years	(18,000)	(4,000)	(17,000)
Property segment | Commercial Property
(Favorable)/Unfavorable Reserve Development
Prior accident years	(10,000)	(11,000)
Property segment | Homeowners Property
(Favorable)/Unfavorable Reserve Development
Prior accident years			(2,000)
Surety Segment
(Favorable)/Unfavorable Reserve Development
Prior accident years	(9,288)	(8,853)	(10,427)
Surety Segment | Contract
(Favorable)/Unfavorable Reserve Development
Prior accident years	(5,000)	(3,000)	(5,000)
Surety Segment | Commercial
(Favorable)/Unfavorable Reserve Development
Prior accident years	(5,000)	(6,000)	(4,000)
Primary Occurrence | Casualty Segment | General liability
(Favorable)/Unfavorable Reserve Development
Prior accident years	(13,000)	(13,000)	(28,000)
Primary Occurrence | Casualty Segment | Small commercial
(Favorable)/Unfavorable Reserve Development
Prior accident years	9,000		(5,000)
Excess Occurrence | Casualty Segment | Commercial Products
(Favorable)/Unfavorable Reserve Development
Prior accident years	(18,000)	(15,000)	(6,000)
Excess Occurrence | Casualty Segment | Personal Umbrella
(Favorable)/Unfavorable Reserve Development
Prior accident years	(3,000)	(11,000)	(4,000)
Claims Made | Casualty Segment | Executive products
(Favorable)/Unfavorable Reserve Development
Prior accident years	(11,000)	(12,000)	(4,000)
Claims Made | Casualty Segment | Professional services
(Favorable)/Unfavorable Reserve Development
Prior accident years	$ (10,000)	$ (10,000)	$ (19,000)