Premiums and Reinsurance Related Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Written premiums:
Written premiums, direct	$ 3,303,682	$ 3,037,932	$ 9,723,219	$ 8,762,249
Written premiums, assumed	329,596	315,273	990,587	977,047
Written premiums, ceded	(576,002)	(504,746)	(1,678,460)	(1,504,497)
Total net premiums written	3,057,276	2,848,459	9,035,346	8,234,799
Earned premiums:
Earned premiums, direct	3,141,883	2,825,176	9,127,399	8,217,888
Earned premiums, assumed	346,780	316,134	1,012,804	913,795
Earned premiums, ceded	(561,840)	(499,396)	(1,602,618)	(1,445,610)
Net premiums earned	2,926,823	2,641,914	8,537,585	7,686,073
Ceded losses and loss expenses incurred	319,472	320,995	952,666	970,267
Ceded commissions earned	$ 129,916	$ 118,207	$ 374,618	$ 354,148