Segment Information - Summary of Operating Results by Segment (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023 USD ($) State	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) State Subsidiary segment	Jun. 30, 2022 USD ($)
Segment Reporting [Abstract]
Number of insurance companies | Subsidiary			12
Number of states in which company operates | State	11		11
Number of reportable segments | segment			1
Segment Reporting Information [Line Items]
Net premiums earned	$ 1,034,469	$ 987,512	$ 2,039,173	$ 1,950,062
Losses and loss adjustment expenses	897,810	826,779	1,827,339	1,648,713
Underwriting expenses	241,200	225,900	475,300	458,400
Underwriting gain (loss)	(104,500)	(65,200)	(263,400)	(157,000)
Net investment income	58,350	38,555	110,323	73,906
Net realized investment losses	(19,778)	(241,938)	29,229	(437,024)
Other income	10,186	1,496	11,081	4,142
Interest expense	(5,549)	(4,274)	(10,479)	(8,548)
Pre-tax loss	(61,210)	(271,340)	(123,288)	(524,469)
Net loss	(41,543)	(210,681)	(86,831)	(407,599)
Property & Casualty
Segment Reporting Information [Line Items]
Net premiums earned	1,027,270	980,304	2,024,832	1,935,722
Losses and loss adjustment expenses	893,900	823,000	1,819,700	1,641,300
Underwriting expenses	237,400	224,500	468,000	453,700
Underwriting gain (loss)	(104,000)	(67,200)	(262,900)	(159,300)
Other
Segment Reporting Information [Line Items]
Net premiums earned	7,200	7,200	14,400	14,400
Losses and loss adjustment expenses	3,900	3,800	7,600	7,400
Underwriting expenses	3,800	1,400	7,300	4,700
Underwriting gain (loss)	$ (500)	$ 2,000	$ (500)	$ 2,300