Segment Information - Summary of Operating Results by Segment (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($) segment State Subsidiary	Mar. 31, 2022 USD ($)
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	$ 1,004,704	$ 962,550
Losses and loss adjustment expenses	929,529	821,933
Underwriting expenses	234,300	232,400
Underwriting gain (loss)	(159,100)	(91,700)
Net investment income	51,973	35,351
Net realized investment gains (losses)	49,008	(195,086)
Other income	894	2,646
Interest expense	(4,931)	(4,275)
Pre-tax loss	(62,078)	(253,129)
Net loss	(45,288)	(196,917)
Property & Casualty
Segment Reporting Information [Line Items]
Net premiums earned	997,562	955,418
Losses and loss adjustment expenses	925,800	818,300
Underwriting expenses	230,800	229,100
Underwriting gain (loss)	(159,000)	(92,000)
Other
Segment Reporting Information [Line Items]
Net premiums earned	7,100	7,200
Losses and loss adjustment expenses	3,700	3,600
Underwriting expenses	3,500	3,300
Underwriting gain (loss)	$ (100)	$ 300