Premiums and Reinsurance Related Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021
Written premiums:
Written premiums, direct	$ 2,738,754	$ 2,542,336
Written premiums, assumed	310,563	317,500
Written premiums, ceded	(474,493)	(446,582)
Total net premiums written	2,574,824	2,413,254
Earned premiums:
Earned premiums, direct	2,667,063	2,404,597
Earned premiums, assumed	295,230	292,373
Earned premiums, ceded	(470,861)	(447,883)
Net premiums earned	2,491,432	2,249,087
Ceded losses and loss expenses incurred	315,476	243,294
Ceded commissions earned	118,418	117,445
Cumulative effect adjustment resulting from changes in accounting principles	$ 8,703	$ 7,655	$ 8,064	$ 7,713