Operating Segment Information - Summary of Selected Information by Operating Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Revenues
Net premiums earned	$ 307,723	$ 269,152
Net investment income	27,084	17,883
Net realized gains	14,620	5,588
Net unrealized gains (losses) on equity securities	15,496	(27,810)
Consolidated revenue	364,923	264,813
Net Earnings
Net underwriting income	67,890	59,478
Net investment income	27,084	17,883
Net realized gains	14,620	5,588
Net unrealized gains (losses) on equity securities	15,496	(27,810)
General corporate expense and interest on debt	(6,222)	(5,373)
Equity in earnings of unconsolidated investees	3,923	8,759
Earnings (loss) before income taxes	122,791	58,525
Income tax expense	23,980	10,602
Net earnings (loss)	98,811	47,923
Casualty Segment
Revenues
Net premiums earned	186,031	171,756
Net Earnings
Net underwriting income	31,831	27,647
Property Segment
Revenues
Net premiums earned	88,767	67,440
Net Earnings
Net underwriting income	28,383	22,476
Surety Segment
Revenues
Net premiums earned	32,925	29,956
Net Earnings
Net underwriting income	$ 7,676	$ 9,355