Related-Party Transactions - Reinsurance Agreement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Related Party Transaction [Line Items]
Premiums receivable	$ 100,700	$ 75,297
Deferred acquisition costs, net	107,342	81,535	$ 58,572
TOTAL ASSETS	1,312,518	1,041,871
Losses payable	55,516	34,482
Provision for unpaid losses and loss adjustment expenses	111,741	74,869	$ 54,988
Unearned premiums	235,462	175,199
Commissions payable	77,075	60,603
TOTAL LIABILITIES	945,149	771,070
Earned premium	403,061	295,824
Ceding commission	191,150	140,983
Losses and loss adjustment expenses	182,402	122,080
Total operating expenses	855,154	629,149
Affiliated Entity | Reinsurance Agreement | Markel
Related Party Transaction [Line Items]
Premiums receivable	97,897	72,697
Deferred acquisition costs, net	103,869	78,449
TOTAL ASSETS	201,766	151,146
Losses payable	53,800	33,459
Provision for unpaid losses and loss adjustment expenses	106,436	70,680
Unearned premiums	227,192	167,541
Commissions payable	75,898	59,511
TOTAL LIABILITIES	463,326	331,191
Earned premium	386,696	281,794
Ceding commission	184,124	134,946
Losses and loss adjustment expenses	182,340	116,396
Total operating expenses	$ 366,464	$ 251,342