Segment Information - Summary of Operating Results by Segment (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2025 USD ($) Subsidiary State segment	Mar. 31, 2024 USD ($)
Segment Reporting [Abstract]
Number of insurance companies | Subsidiary	12
Number of states in which company operates | State	11
Number of reportable segments | segment	1
Segment Reporting Information [Line Items]
Net premiums earned	$ 1,283,069	$ 1,166,679
Total incurred losses and loss adjustment expenses	1,220,813	903,965
Policy acquisition costs	228,720	196,040
Other operating expenses	79,453	77,087
Net investment income	81,479	65,018
Net realized investment gains	23,321	38,192
Other income	6,010	4,196
Interest expense	(7,189)	(7,773)
(Loss) income before income taxes	(142,296)	89,220
Net (loss) income	(108,327)	73,462
Operating Segments
Segment Reporting Information [Line Items]
Net premiums earned	1,283,100	1,166,700
Losses	1,069,300	785,800
Loss adjustment expenses	151,500	118,200
Total incurred losses and loss adjustment expenses	1,220,800	904,000
Policy acquisition costs	228,700	196,000
Other operating expenses	79,500	77,100
Underwriting loss	(245,900)	(10,400)
Net investment income	81,500	65,000
Net realized investment gains	23,300	38,200
Other income	6,000	4,200
Interest expense	(7,200)	(7,800)
(Loss) income before income taxes	(142,300)	89,200
Net (loss) income	(108,300)	73,500
Property & Casualty
Segment Reporting Information [Line Items]
Net premiums earned	1,275,758	1,159,369
Property & Casualty | Operating Segments
Segment Reporting Information [Line Items]
Net premiums earned	1,275,800	1,159,400
Losses	1,065,600	782,200
Loss adjustment expenses	151,000	117,800
Total incurred losses and loss adjustment expenses	1,216,600	900,000
Policy acquisition costs	225,800	193,100
Other operating expenses	78,900	76,200
Underwriting loss	(245,500)	(9,900)
Other | Operating Segments
Segment Reporting Information [Line Items]
Net premiums earned	7,300	7,300
Losses	3,700	3,600
Loss adjustment expenses	500	400
Total incurred losses and loss adjustment expenses	4,200	4,000
Policy acquisition costs	2,900	2,900
Other operating expenses	600	900
Underwriting loss	$ (400)	$ (500)