Segment Information - Summary of Operating Results by Segment (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($) State	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) segment State Subsidiary	Jun. 30, 2021 USD ($)
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	$ 987,512	$ 926,820	$ 1,950,062	$ 1,842,741
Losses and loss adjustment expenses	826,779	657,228	1,648,713	1,283,572
Underwriting expenses	225,900	222,000	458,400	451,800
Underwriting gain (loss)	(65,200)	47,600	(157,000)	107,300
Net investment income	38,555	30,953	73,906	63,232
Net realized investment (losses) gains	(241,938)	58,805	(437,024)	100,496
Other income	1,496	2,197	4,142	5,402
Interest expense	(4,274)	(4,235)	(8,548)	(8,577)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	(271,340)	135,401	(524,469)	267,823
Net (loss) income	(210,681)	109,181	(407,599)	216,176
Property & Casualty
Segment Reporting Information [Line Items]
Net premiums earned	980,304	919,515	1,935,722	1,828,330
Losses and loss adjustment expenses	823,000	653,600	1,641,300	1,276,500
Underwriting expenses	224,500	218,100	453,700	445,100
Underwriting gain (loss)	(67,200)	47,800	(159,300)	106,700
Other
Segment Reporting Information [Line Items]
Net premiums earned	7,200	7,300	14,400	14,400
Losses and loss adjustment expenses	3,800	3,600	7,400	7,100
Underwriting expenses	1,400	3,900	4,700	6,700
Underwriting gain (loss)	$ 2,000	$ (200)	$ 2,300	$ 600