Operating Segment Information - Summary of Selected Information by Operating Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Revenues
Net premiums earned	$ 269,152	$ 228,595
Net investment income	17,883	16,424
Net realized gains	5,588	14,150
Net unrealized gains (losses) on equity securities	(27,810)	28,162
Consolidated revenue	264,813	287,331
Net Earnings
Net underwriting income	59,478	29,917
Net investment income	17,883	16,424
Net realized gains	5,588	14,150
Net unrealized gains (losses) on equity securities	(27,810)	28,162
General corporate expense and interest on debt	(5,373)	(5,243)
Equity in earnings of unconsolidated investees	8,759	6,424
Earnings before income taxes	58,525	89,834
Income tax expense	10,602	16,822
Net earnings	47,923	73,012
Casualty Segment
Revenues
Net premiums earned	171,756	148,770
Net Earnings
Net underwriting income	27,647	24,867
Property Segment
Revenues
Net premiums earned	67,440	51,642
Net Earnings
Net underwriting income	22,476	(1,005)
Surety Segment
Revenues
Net premiums earned	29,956	28,183
Net Earnings
Net underwriting income	$ 9,355	$ 6,055