Segment Information (Gross Premiums Earned and Reconciliation to Net Premiums) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Segment net premiums earned	$ 243,160	$ 242,420	$ 727,176	$ 730,068
Specialty P&C Segment
Segment Reporting Information [Line Items]
Segment net premiums earned	188,704	195,772	562,137	562,206
Specialty P&C Segment | Operating segments
Segment Reporting Information [Line Items]
Ceded premiums earned	(17,204)	(9,914)	(52,092)	(57,524)
Segment net premiums earned	188,704	195,772	562,137	562,206
Specialty P&C Segment | MPL | Operating segments
Segment Reporting Information [Line Items]
Gross premiums earned:	186,376	183,501	551,791	553,644
Specialty P&C Segment | Medical Technology Liability | Operating segments
Segment Reporting Information [Line Items]
Gross premiums earned:	11,262	10,904	33,196	32,060
Specialty P&C Segment | Lloyd's Syndicates | Operating segments
Segment Reporting Information [Line Items]
Gross premiums earned:	2,897	4,931	12,256	14,499
Specialty P&C Segment | Other | Operating segments
Segment Reporting Information [Line Items]
Gross premiums earned:	5,373	6,350	16,986	19,527
Workers' Compensation Insurance Segment
Segment Reporting Information [Line Items]
Segment net premiums earned	41,829	39,885	124,692	121,706
Workers' Compensation Insurance Segment | Operating segments
Segment Reporting Information [Line Items]
Ceded premiums earned	(19,993)	(20,849)	(60,748)	(62,338)
Segment net premiums earned	41,829	39,885	124,692	121,706
Workers' Compensation Insurance Segment | Traditional business | Operating segments
Segment Reporting Information [Line Items]
Gross premiums earned:	46,148	43,423	136,310	131,623
Workers' Compensation Insurance Segment | Alternative market business | Operating segments
Segment Reporting Information [Line Items]
Gross premiums earned:	15,674	17,311	49,130	52,421
Segregated Portfolio Cell Reinsurance Segment
Segment Reporting Information [Line Items]
Segment net premiums earned	12,627	6,763	40,347	46,156
Segregated Portfolio Cell Reinsurance Segment | Operating segments
Segment Reporting Information [Line Items]
Ceded premiums earned	(1,986)	(2,245)	(6,301)	(6,845)
Segment net premiums earned	12,627	6,763	40,347	46,156
Segregated Portfolio Cell Reinsurance Segment | MPL | Operating segments
Segment Reporting Information [Line Items]
Gross premiums earned:	518	(6,971)	1,881	4,388
Segregated Portfolio Cell Reinsurance Segment | Workers' compensation | Operating segments
Segment Reporting Information [Line Items]
Gross premiums earned:	$ 14,095	$ 15,979	$ 44,767	$ 48,613