Operating Segment Information - Summary of Selected Information by Operating Segment (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Revenues
Net premiums earned	$ 291,468			$ 253,389			$ 843,430	$ 722,984
Net investment income	21,270			17,844			57,625	50,929
Net realized gains	573,170			1,829			591,562	52,442
Net unrealized gains (losses) on equity securities	(26,414)			(2,592)			(155,218)	29,526
Consolidated revenue	859,494			270,470			1,337,399	855,881
Net Earnings
Net underwriting income	8,796			13,724			124,230	80,232
Net investment income	21,270			17,844			57,625	50,929
Net realized gains	573,170			1,829			591,562	52,442
Net unrealized gains (losses) on equity securities	(26,414)			(2,592)			(155,218)	29,526
General corporate expense and interest on debt	(4,768)			(4,411)			(14,587)	(15,244)
Equity in earnings (loss) of unconsolidated investees	(17,352)			9,043			3,061	29,407
Earnings (loss) before income taxes	554,702			35,437			606,673	227,292
Income tax expense	114,809			6,194			121,096	43,222
Net earnings (loss)	439,893	$ (2,239)	$ 47,923	29,243	$ 81,815	$ 73,012	485,577	184,070
Casualty Segment
Revenues
Net premiums earned	179,615			162,852			528,494	467,817
Net Earnings
Net underwriting income	11,329			22,949			60,418	74,254
Property Segment
Revenues
Net premiums earned	80,844			60,886			222,974	168,393
Net Earnings
Net underwriting income	(8,308)			(16,558)			40,273	(8,684)
Surety Segment
Revenues
Net premiums earned	31,009			29,651			91,962	86,774
Net Earnings
Net underwriting income	$ 5,775			$ 7,333			$ 23,539	$ 14,662