Operating Segment Information - Summary by Operating Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Revenues
Net premiums earned	$ 360,676	$ 307,723
Net investment income	32,847	27,084
Net realized gains	5,994	14,620
Net unrealized gains on equity securities	45,314	15,496
Consolidated revenue	444,831	364,923
Net Earnings
Net underwriting income	77,695	67,890
Net investment income	32,847	27,084
Net realized gains	5,994	14,620
Net unrealized gains on equity securities	45,314	15,496
General corporate expense and interest on debt	(6,628)	(6,222)
Equity in earnings of unconsolidated investees	4,769	3,923
Earnings before income taxes	159,991	122,791
Income tax expense	32,091	23,980
Net earnings	127,900	98,811
Casualty Segment
Revenues
Net premiums earned	198,276	186,031
Net Earnings
Net underwriting income	13,674	31,831
Property Segment
Revenues
Net premiums earned	129,411	88,767
Net Earnings
Net underwriting income	57,716	28,383
Surety Segment
Revenues
Net premiums earned	32,989	32,925
Net Earnings
Net underwriting income	$ 6,305	$ 7,676