Segment Information - Summary of Operating Results by Segment (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($) State	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) Subsidiary segment State	Sep. 30, 2021 USD ($)
Segment Reporting [Abstract]
Number of insurance companies | Subsidiary			13
Number of states in which company operates | State	11		11
Number of reportable segments | segment			1
Segment Reporting Information [Line Items]
Net premiums earned	$ 996,939	$ 940,941	$ 2,947,000	$ 2,783,682
Losses and loss adjustment expenses	787,462	697,947	2,436,175	1,981,519
Underwriting expenses	237,400	233,400	695,800	685,500
Underwriting gain (loss)	(28,000)	9,600	(185,000)	116,700
Net investment income	44,563	32,334	118,469	95,566
Net realized investment losses	(144,213)	(43,543)	(581,237)	56,953
Other income	2,998	2,481	7,141	7,883
Interest expense	(4,273)	(4,267)	(12,822)	(12,845)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	(128,903)	(3,381)	(653,373)	264,441
Net (loss) income	(98,303)	1,288	(505,902)	217,464
Property & Casualty
Segment Reporting Information [Line Items]
Net premiums earned	989,688	933,605	2,925,410	2,761,934
Losses and loss adjustment expenses	783,800	694,200	2,425,100	1,970,800
Underwriting expenses	233,600	229,700	687,300	675,100
Underwriting gain (loss)	(27,700)	9,700	(187,000)	116,000
Other
Segment Reporting Information [Line Items]
Net premiums earned	7,200	7,300	21,600	21,800
Losses and loss adjustment expenses	3,700	3,700	11,100	10,700
Underwriting expenses	3,800	3,700	8,500	10,400
Underwriting gain (loss)	$ (300)	$ (100)	$ 2,000	$ 700