Segment Information - Summary of Operating Results by Segment (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($) State Subsidiary segment	Mar. 31, 2023 USD ($)
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	$ 1,166,679	$ 1,004,704
Losses and loss adjustment expenses	903,965	929,529
Underwriting expenses	273,100	234,300
Underwriting gain (loss)	(10,400)	(159,100)
Net investment income	65,018	51,973
Net realized investment gains	38,192	49,008
Other income	4,196	894
Interest expense	(7,773)	(4,931)
Pre-tax income (loss)	89,220	(62,078)
Net income (loss)	73,462	(45,288)
Property & Casualty
Segment Reporting Information [Line Items]
Net premiums earned	1,159,369	997,562
Losses and loss adjustment expenses	900,000	925,800
Underwriting expenses	269,300	230,800
Underwriting gain (loss)	(9,900)	(159,000)
Other
Segment Reporting Information [Line Items]
Net premiums earned	7,300	7,100
Losses and loss adjustment expenses	4,000	3,700
Underwriting expenses	3,800	3,500
Underwriting gain (loss)	$ (500)	$ (100)