Premiums and Reinsurance Related Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Written premiums:
Written premiums, direct	$ 3,610,784	$ 3,380,470	$ 6,921,677	$ 6,419,537
Written premiums, assumed	366,985	337,302	740,031	660,991
Written premiums, ceded	(626,330)	(590,993)	(1,176,966)	(1,102,458)
Total net premiums written	3,351,439	3,126,779	6,484,742	5,978,070
Earned premiums:
Earned premiums, direct	3,335,252	3,048,872	6,569,095	5,985,516
Earned premiums, assumed	336,521	328,114	676,118	666,024
Earned premiums, ceded	(573,588)	(530,571)	(1,134,647)	(1,040,778)
Net premiums earned	3,098,185	2,846,415	6,110,566	5,610,762
Ceded losses and loss expenses incurred	354,923	327,243	669,175	633,194
Ceded commissions earned	$ 135,919	$ 123,647	$ 275,523	$ 244,701