Segment Information (Net Premiums) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting, Revenue Reconciling Item [Line Items]
Total net premiums earned	$ 962,823	$ 1,055,082	$ 1,086,972
Property and casualty business
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	77,283	33,679	25,412
Other	1,674	2,678	2,942
Total net premiums earned	962,823	1,055,082	1,086,972
Property and casualty business | Other liability
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	299,961	316,098	318,412
Property and casualty business | Fire and allied lines
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	253,485	277,515	285,205
Property and casualty business | Automobile
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	255,279	324,420	345,637
Property and casualty business | Workers' compensation
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	61,690	75,953	87,376
Property and casualty business | Fidelity and surety
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums earned	30,989	28,001	25,539
Property and casualty business | Reinsurance assumed
Segment Reporting, Revenue Reconciling Item [Line Items]
Reinsurance assumed	$ 59,745	$ 30,417	$ 21,861