Segment Information (Net Premiums) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting, Revenue Reconciling Item [Line Items]
Total net premiums earned	$ 951,541	$ 962,823	$ 1,055,082
Property and casualty business
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	163,980	77,283	33,679
Other	1,131	1,674	2,678
Total net premiums earned	951,541	962,823	1,055,082
Property and casualty business | Other liability
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	302,446	299,961	316,098
Property and casualty business | Fire and allied lines
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	237,113	253,485	277,515
Property and casualty business | Automobile
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	208,399	255,279	324,420
Property and casualty business | Workers' compensation
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	56,015	61,690	75,953
Property and casualty business | Fidelity and surety
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	37,975	30,989	28,001
Property and casualty business | Reinsurance assumed
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	$ 108,462	$ 59,745	$ 30,417