Schedule VI - Supplementary Information Concerning Property-Casualty Insurance Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract]
Deferred policy acquisition costs	$ 861,609	$ 763,486	$ 676,145
Reserves for losses and loss expenses	18,739,652	17,011,223	15,390,888
Unearned premiums	5,922,326	5,297,654	4,847,160
Net premiums earned	10,400,687	9,561,429	8,106,031
Net investment income	1,052,835	779,185	671,618
Losses and loss expenses incurred:
Current year	6,311,780	5,774,713	4,921,191
Prior years	29,681	54,511	863
Loss reserve discount accretion	30,681	32,526	31,906
Amortization of deferred policy acquisition costs		1,038,903	961,628
Paid losses and loss expenses	4,981,610	4,347,910	3,665,694
Net premiums written	$ 10,954,467	$ 10,004,070	$ 8,862,867