SCHEDULE III - SUPPLEMENTARY INSURANCE INFORMATION (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Supplementary Insurance Information [Line Items]
Deferred acquisition costs	$ 524,837	$ 450,950	$ 473,569
Reserve for losses and loss expenses	17,218,929	16,434,018	15,168,863
Unearned premiums	5,211,865	4,747,602	4,361,447
Net premiums earned	5,306,235	5,083,781	5,160,326
Net investment income	759,229	611,742	418,829
Net losses and loss expenses	3,158,487	3,393,102	3,242,410
Acquisition costs	1,070,551	1,000,945	1,022,017
Other operating expenses	666,202	684,446	680,343
Net premiums written	5,757,351	5,102,325	5,263,056
Operating Segments | Insurance
Supplementary Insurance Information [Line Items]
Deferred acquisition costs	343,476	298,249	249,407
Reserve for losses and loss expenses	10,499,703	9,507,409	8,381,593
Unearned premiums	3,859,162	3,507,519	3,077,628
Net premiums earned	3,926,036	3,461,700	3,134,155
Net investment income	0	0	0
Net losses and loss expenses	2,245,420	2,080,001	1,785,854
Acquisition costs	766,915	648,463	577,838
Other operating expenses	485,929	472,094	443,704
Net premiums written	4,250,545	3,758,720	3,377,906
Operating Segments | Reinsurance
Supplementary Insurance Information [Line Items]
Deferred acquisition costs	181,361	152,701	224,162
Reserve for losses and loss expenses	6,719,226	6,926,609	6,787,270
Unearned premiums	1,352,703	1,240,083	1,283,819
Net premiums earned	1,380,199	1,622,081	2,026,171
Net investment income	0	0	0
Net losses and loss expenses	913,067	1,313,101	1,456,556
Acquisition costs	303,636	352,482	444,179
Other operating expenses	50,513	79,373	106,585
Net premiums written	1,506,806	1,343,605	1,885,150
Corporate
Supplementary Insurance Information [Line Items]
Deferred acquisition costs	0	0	0
Reserve for losses and loss expenses	0	0	0
Unearned premiums	0	0	0
Net premiums earned	0	0	0
Net investment income	759,229	611,742	418,829
Net losses and loss expenses	0	0	0
Acquisition costs	0	0	0
Other operating expenses	129,760	132,979	130,054
Net premiums written	$ 0	$ 0	$ 0